Flutter for Xamarin.Forms developers

This document is meant for Xamarin.Forms developers looking to apply their existing knowledge to build mobile apps with Flutter. If you understand the fundamentals of the Xamarin.Forms framework, then you can use this document as a jump start to Flutter development.

Your Android and iOS knowledge and skill set are valuable when building with Flutter, because Flutter relies on the native operating system configurations, similar to how you would configure your native Xamarin.Forms projects. The Flutter Frameworks is also similar to how you create a single UI, that is used on multiple platforms.

This document can be used as a cookbook by jumping around and finding questions that are most relevant to your needs.

For each platform in Xamarin.Forms, you call the LoadApplication method, which creates a new application and starts your app.

LoadApplication(new App());

In Flutter, the default main entry point is main where you load your Flutter app.

void main() {
  runApp(const MyApp());
}

In Xamarin.Forms, you assign a Page to the MainPage property in the Application class.

public class App : Application
{
    public App()
    {
        MainPage = new ContentPage
        {
            Content = new Label
            {
                Text = "Hello World",
                HorizontalOptions = LayoutOptions.Center,
                VerticalOptions = LayoutOptions.Center
            }
        };
    }
}

In Flutter, "everything is a widget", even the application itself. The following example shows MyApp, a simple application Widget.

class MyApp extends StatelessWidget {
  /// This widget is the root of your application.
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const Center(
      child: Text(
        'Hello World!',
        textDirection: TextDirection.ltr,
      ),
    );
  }
}

Xamarin.Forms has many types of pages; ContentPage is the most common. In Flutter, you specify an application widget that holds your root page. You can use a MaterialApp widget, which supports Material Design, or you can use a CupertinoApp widget, which supports an iOS-style app, or you can use the lower level WidgetsApp, which you can customize in any way you want.

The following code defines the home page, a stateful widget. In Flutter, all widgets are immutable, but two types of widgets are supported: Stateful and Stateless. Examples of a stateless widget are titles, icons, or images.

The following example uses MaterialApp, which holds its root page in the home property.

class MyApp extends StatelessWidget {
  /// This widget is the root of your application.
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

From here, your actual first page is another Widget, in which you create your state.

A Stateful widget, such as MyHomePage below, consists of two parts. The first part, which is itself immutable, creates a State object that holds the state of the object. The State object persists over the life of the widget.

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

The State object implements the build() method for the stateful widget.

When the state of the widget tree changes, call setState(), which triggers a build of that portion of the UI. Make sure to call setState() only when necessary, and only on the part of the widget tree that has changed, or it can result in poor UI performance.

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        // Take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set the appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

In Flutter, the UI (also known as widget tree), is immutable, meaning you can't change its state once it's built. You change fields in your State class, then call setState() to rebuild the entire widget tree again.

This way of generating UI is different from Xamarin.Forms, but there are many benefits to this approach.

ContentPage, TabbedPage, FlyoutPage are all types of pages you might use in a Xamarin.Forms application. These pages would then hold Elements to display the various controls. In Xamarin.Forms an Entry or Button are examples of an Element.

In Flutter, almost everything is a widget. A Page, called a Route in Flutter, is a widget. Buttons, progress bars, and animation controllers are all widgets. When building a route, you create a widget tree.

Flutter includes the Material Components library. These are widgets that implement the Material Design guidelines. Material Design is a flexible design system optimized for all platforms, including iOS.

But Flutter is flexible and expressive enough to implement any design language. For example, on iOS, you can use the Cupertino widgets to produce an interface that looks like Apple's iOS design language.

In Xamarin.Forms, each Page or Element is a stateful class, that has properties and methods. You update your Element by updating a property, and this is propagated down to the native control.

In Flutter, Widgets are immutable and you can't directly update them by changing a property, instead you have to work with the widget's state.

This is where the concept of Stateful vs Stateless widgets comes from. A StatelessWidget is just what it sounds like— a widget with no state information.

StatelessWidgets are useful when the part of the user interface you are describing doesn't depend on anything other than the configuration information in the object.

For example, in Xamarin.Forms, this is similar to placing an Image with your logo. The logo is not going to change during runtime, so use a StatelessWidget in Flutter.

If you want to dynamically change the UI based on data received after making an HTTP call or a user interaction, then you have to work with StatefulWidget and tell the Flutter framework that the widget's State has been updated, so it can update that widget.

The important thing to note here is at the core both stateless and stateful widgets behave the same. They rebuild every frame, the difference is the StatefulWidget has a State object that stores state data across frames and restores it.

If you are in doubt, then always remember this rule: if a widget changes (because of user interactions, for example) it's stateful. However, if a widget reacts to change, the containing parent widget can still be stateless if it doesn't itself react to change.

The following example shows how to use a StatelessWidget. A common StatelessWidget is the Text widget. If you look at the implementation of the Text widget you'll find it subclasses StatelessWidget.

const Text(
  'I like Flutter!',
  style: TextStyle(fontWeight: FontWeight.bold),
);

As you can see, the Text widget has no state information associated with it, it renders what is passed in its constructors and nothing more.

But, what if you want to make "I Like Flutter" change dynamically, for example, when clicking a FloatingActionButton?

To achieve this, wrap the Text widget in a StatefulWidget and update it when the user clicks the button, as shown in the following example:

import 'package:flutter/material.dart';

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  /// This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  /// Default placeholder text
  String textToShow = 'I Like Flutter';

  void _updateText() {
    setState(() {
      // Update the text
      textToShow = 'Flutter is Awesome!';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: Center(child: Text(textToShow)),
      floatingActionButton: FloatingActionButton(
        onPressed: _updateText,
        tooltip: 'Update Text',
        child: const Icon(Icons.update),
      ),
    );
  }
}

In Xamarin.Forms, most developers write layouts in XAML, though sometimes in C#. In Flutter, you write your layouts with a widget tree in code.

The following example shows how to display a simple widget with padding:

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(title: const Text('Sample App')),
    body: Center(
      child: ElevatedButton(
        style: ElevatedButton.styleFrom(
          padding: const EdgeInsets.only(left: 20, right: 30),
        ),
        onPressed: () {},
        child: const Text('Hello'),
      ),
    ),
  );
}

You can view the layouts that Flutter has to offer in the widget catalog.

In Xamarin.Forms, you had to remove or add an Element in code. This involved either setting the Content property or calling Add() or Remove() if it was a list.

In Flutter, because widgets are immutable there is no direct equivalent. Instead, you can pass a function to the parent that returns a widget, and control that child's creation with a boolean flag.

The following example shows how to toggle between two widgets when the user clicks the FloatingActionButton:

class SampleApp extends StatelessWidget {
  /// This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  /// Default value for toggle
  bool toggle = true;
  void _toggle() {
    setState(() {
      toggle = !toggle;
    });
  }

  Widget _getToggleChild() {
    if (toggle) {
      return const Text('Toggle One');
    }
    return CupertinoButton(
      onPressed: () {},
      child: const Text('Toggle Two'),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: Center(child: _getToggleChild()),
      floatingActionButton: FloatingActionButton(
        onPressed: _toggle,
        tooltip: 'Update Text',
        child: const Icon(Icons.update),
      ),
    );
  }
}

In Xamarin.Forms, you create simple animations using ViewExtensions that include methods such as FadeTo and TranslateTo. You would use these methods on a view to perform the required animations.

<Image Source="{Binding MyImage}" x:Name="myImage" />

Then in code behind, or a behavior, this would fade in the image, over a 1-second period.

myImage.FadeTo(0, 1000);

In Flutter, you animate widgets using the animation library by wrapping widgets inside an animated widget. Use an AnimationController, which is an Animation<double> that can pause, seek, stop and reverse the animation. It requires a Ticker that signals when vsync happens, and produces a linear interpolation between 0 and 1 on each frame while it's running. You then create one or moreAnimations and attach them to the controller.

For example, you might use CurvedAnimation to implement an animation along an interpolated curve. In this sense, the controller is the "master" source of the animation progress and the CurvedAnimation computes the curve that replaces the controller's default linear motion. Like widgets, animations in Flutter work with composition.

When building the widget tree, you assign the Animation to an animated property of a widget, such as the opacity of a FadeTransition, and tell the controller to start the animation.

The following example shows how to write a FadeTransition that fades the widget into a logo when you press the FloatingActionButton:

import 'package:flutter/material.dart';

void main() {
  runApp(const FadeAppTest());
}

class FadeAppTest extends StatelessWidget {
  /// This widget is the root of your application.
  const FadeAppTest({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Fade Demo',
      home: MyFadeTest(title: 'Fade Demo'),
    );
  }
}

class MyFadeTest extends StatefulWidget {
  const MyFadeTest({super.key, required this.title});

  final String title;

  @override
  State<MyFadeTest> createState() => _MyFadeTest();
}

class _MyFadeTest extends State<MyFadeTest> with TickerProviderStateMixin {
  late final AnimationController controller;
  late final CurvedAnimation curve;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      duration: const Duration(milliseconds: 2000),
      vsync: this,
    );
    curve = CurvedAnimation(
      parent: controller,
      curve: Curves.easeIn,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.title)),
      body: Center(
        child: FadeTransition(
          opacity: curve,
          child: const FlutterLogo(size: 100),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          controller.forward();
        },
        tooltip: 'Fade',
        child: const Icon(Icons.brush),
      ),
    );
  }
}

For more information, see Animation & Motion widgets, the Animations tutorial, and the Animations overview.

Xamarin.Forms never had a built-in way to draw directly on the screen. Many would use SkiaSharp, if they needed a custom image drawn. In Flutter, you have direct access to the Skia Canvas and can easily draw on screen.

Flutter has two classes that help you draw to the canvas: CustomPaint and CustomPainter, the latter of which implements your algorithm to draw to the canvas.

To learn how to implement a signature painter in Flutter, see Collin's answer on Custom Paint.

import 'package:flutter/material.dart';

void main() {
  runApp(const MaterialApp(home: DemoApp()));
}

class DemoApp extends StatelessWidget {
  const DemoApp({super.key});

  @override
  Widget build(BuildContext context) => const Scaffold(body: Signature());
}

class Signature extends StatefulWidget {
  const Signature({super.key});

  @override
  SignatureState createState() => SignatureState();
}

class SignatureState extends State<Signature> {
  List<Offset?> _points = <Offset?>[];

  void _onPanUpdate(DragUpdateDetails details) {
    setState(() {
      final RenderBox referenceBox = context.findRenderObject() as RenderBox;
      final Offset localPosition = referenceBox.globalToLocal(
        details.globalPosition,
      );
      _points = List.from(_points)..add(localPosition);
    });
  }

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onPanUpdate: _onPanUpdate,
      onPanEnd: (details) => _points.add(null),
      child: CustomPaint(
        painter: SignaturePainter(_points),
        size: Size.infinite,
      ),
    );
  }
}

class SignaturePainter extends CustomPainter {
  const SignaturePainter(this.points);

  final List<Offset?> points;

  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()
      ..color = Colors.black
      ..strokeCap = StrokeCap.round
      ..strokeWidth = 5;
    for (int i = 0; i < points.length - 1; i++) {
      if (points[i] != null && points[i + 1] != null) {
        canvas.drawLine(points[i]!, points[i + 1]!, paint);
      }
    }
  }

  @override
  bool shouldRepaint(SignaturePainter oldDelegate) =>
      oldDelegate.points != points;
}

On Xamarin.Forms, all VisualElements have an Opacity. In Flutter, you need to wrap a widget in an Opacity widget to accomplish this.

In Xamarin.Forms, you typically subclass VisualElement, or use a pre-existing VisualElement, to override and implement methods that achieve the desired behavior.

In Flutter, build a custom widget by composing smaller widgets (instead of extending them). It is somewhat similar to implementing a custom control based off a Grid with numerous VisualElements added in, while extending with custom logic.

For example, how do you build a CustomButton that takes a label in the constructor? Create a CustomButton that composes a ElevatedButton with a label, rather than by extending ElevatedButton:

class CustomButton extends StatelessWidget {
  const CustomButton(this.label, {super.key});

  final String label;

  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () {},
      child: Text(label),
    );
  }
}

Then use CustomButton, just as you'd use any other Flutter widget:

@override
Widget build(BuildContext context) {
  return const Center(
    child: CustomButton('Hello'),
  );
}

In Xamarin.Forms, the NavigationPage class provides a hierarchical navigation experience where the user is able to navigate through pages, forwards and backwards.

Flutter has a similar implementation, using a Navigator and Routes. A Route is an abstraction for a Page of an app, and a Navigator is a widget that manages routes.

A route roughly maps to a Page. The navigator works in a similar way to the Xamarin.Forms NavigationPage, in that it can push() and pop() routes depending on whether you want to navigate to, or back from, a view.

To navigate between pages, you have a couple options:

• Specify a Map of route names. (MaterialApp)
• Directly navigate to a route. (WidgetsApp)

The following example builds a Map.

void main() {
  runApp(
    MaterialApp(
      home: const MyAppHome(), // becomes the route named '/'
      routes: <String, WidgetBuilder>{
        '/a': (context) => const MyPage(title: 'page A'),
        '/b': (context) => const MyPage(title: 'page B'),
        '/c': (context) => const MyPage(title: 'page C'),
      },
    ),
  );
}

Navigate to a route by pushing its name to the Navigator.

Navigator.of(context).pushNamed('/b');

The Navigator is a stack that manages your app's routes. Pushing a route to the stack moves to that route. Popping a route from the stack, returns to the previous route. This is done by awaiting on the Future returned by push().

async/await is very similar to the .NET implementation and is explained in more detail in Async UI.

For example, to start a location route that lets the user select their location, you might do the following:

Object? coordinates = await Navigator.of(context).pushNamed('/location');

And then, inside your 'location' route, once the user has selected their location, pop the stack with the result:

Navigator.of(context).pop({'lat': 43.821757, 'long': -79.226392});

In Xamarin.Forms, to send the user to another application, you use a specific URI scheme, using Device.OpenUrl("mailto://").

To implement this functionality in Flutter, create a native platform integration, or use an existing plugin, such asurl_launcher, available with many other packages on pub.dev.

Dart has a single-threaded execution model, with support for Isolates (a way to run Dart codes on another thread), an event loop, and asynchronous programming. Unless you spawn an Isolate, your Dart code runs in the main UI thread and is driven by an event loop.

Dart's single-threaded model doesn't mean you need to run everything as a blocking operation that causes the UI to freeze. Much like Xamarin.Forms, you need to keep the UI thread free. You would use async/await to perform tasks, where you must wait for the response.

In Flutter, use the asynchronous facilities that the Dart language provides, also named async/await, to perform asynchronous work. This is very similar to C# and should be very easy to use for any Xamarin.Forms developer.

For example, you can run network code without causing the UI to hang by using async/await and letting Dart do the heavy lifting:

Future<void> loadData() async {
  final Uri dataURL = Uri.parse(
    'https://jsonplaceholder.typicode.com/posts',
  );
  final http.Response response = await http.get(dataURL);
  setState(() {
    data = jsonDecode(response.body);
  });
}

Once the awaited network call is done, update the UI by calling setState(), which triggers a rebuild of the widget subtree and updates the data.

The following example loads data asynchronously and displays it in a ListView:

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List<Map<String, dynamic>> data = <Map<String, dynamic>>[];

  @override
  void initState() {
    super.initState();
    loadData();
  }

  Future<void> loadData() async {
    final Uri dataURL = Uri.parse(
      'https://jsonplaceholder.typicode.com/posts',
    );
    final http.Response response = await http.get(dataURL);
    setState(() {
      data = jsonDecode(response.body);
    });
  }

  Widget getRow(int index) {
    return Padding(
      padding: const EdgeInsets.all(10),
      child: Text('Row ${data[index]['title']}'),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: ListView.builder(
        itemCount: data.length,
        itemBuilder: (context, index) {
          return getRow(index);
        },
      ),
    );
  }
}

Refer to the next section for more information on doing work in the background, and how Flutter differs from Android.

Since Flutter is single threaded and runs an event loop, you don't have to worry about thread management or spawning background threads. This is very similar to Xamarin.Forms. If you're doing I/O-bound work, such as disk access or a network call, then you can safely use async/await and you're all set.

If, on the other hand, you need to do computationally intensive work that keeps the CPU busy, you want to move it to an Isolate to avoid blocking the event loop, like you would keep any sort of work out of the main thread. This is similar to when you move things to a different thread via Task.Run() in Xamarin.Forms.

For I/O-bound work, declare the function as an async function, and await on long-running tasks inside the function:

Future<void> loadData() async {
  final Uri dataURL = Uri.parse(
    'https://jsonplaceholder.typicode.com/posts',
  );
  final http.Response response = await http.get(dataURL);
  setState(() {
    data = jsonDecode(response.body);
  });
}

This is how you would typically do network or database calls, which are both I/O operations.

However, there are times when you might be processing a large amount of data and your UI hangs. In Flutter, use Isolates to take advantage of multiple CPU cores to do long-running or computationally intensive tasks.

Isolates are separate execution threads that do not share any memory with the main execution memory heap. This is a difference between Task.Run(). This means you can't access variables from the main thread, or update your UI by calling setState().

The following example shows, in a simple isolate, how to share data back to the main thread to update the UI.

Future<void> loadData() async {
  final ReceivePort receivePort = ReceivePort();
  await Isolate.spawn(dataLoader, receivePort.sendPort);

  // The 'echo' isolate sends its SendPort as the first message
  final SendPort sendPort = await receivePort.first as SendPort;
  final List<Map<String, dynamic>> msg = await sendReceive(
    sendPort,
    'https://jsonplaceholder.typicode.com/posts',
  );
  setState(() {
    data = msg;
  });
}

// The entry point for the isolate
static Future<void> dataLoader(SendPort sendPort) async {
  // Open the ReceivePort for incoming messages.
  final ReceivePort port = ReceivePort();

  // Notify any other isolates what port this isolate listens to.
  sendPort.send(port.sendPort);
  await for (final dynamic msg in port) {
    final String url = msg[0] as String;
    final SendPort replyTo = msg[1] as SendPort;

    final Uri dataURL = Uri.parse(url);
    final http.Response response = await http.get(dataURL);
    // Lots of JSON to parse
    replyTo.send(jsonDecode(response.body) as List<Map<String, dynamic>>);
  }
}

Future<List<Map<String, dynamic>>> sendReceive(SendPort port, String msg) {
  final ReceivePort response = ReceivePort();
  port.send(<dynamic>[msg, response.sendPort]);
  return response.first as Future<List<Map<String, dynamic>>>;
}

Here, dataLoader() is the Isolate that runs in its own separate execution thread. In the isolate, you can perform more CPU intensive processing (parsing a big JSON, for example), or perform computationally intensive math, such as encryption or signal processing.

You can run the full example below:

import 'dart:async';
import 'dart:convert';
import 'dart:isolate';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List<Map<String, dynamic>> data = <Map<String, dynamic>>[];

  @override
  void initState() {
    super.initState();
    loadData();
  }

  bool get showLoadingDialog => data.isEmpty;

  Future<void> loadData() async {
    final ReceivePort receivePort = ReceivePort();
    await Isolate.spawn(dataLoader, receivePort.sendPort);

    // The 'echo' isolate sends its SendPort as the first message
    final SendPort sendPort = await receivePort.first as SendPort;
    final List<Map<String, dynamic>> msg = await sendReceive(
      sendPort,
      'https://jsonplaceholder.typicode.com/posts',
    );
    setState(() {
      data = msg;
    });
  }

  // The entry point for the isolate
  static Future<void> dataLoader(SendPort sendPort) async {
    // Open the ReceivePort for incoming messages.
    final ReceivePort port = ReceivePort();

    // Notify any other isolates what port this isolate listens to.
    sendPort.send(port.sendPort);
    await for (final dynamic msg in port) {
      final String url = msg[0] as String;
      final SendPort replyTo = msg[1] as SendPort;

      final Uri dataURL = Uri.parse(url);
      final http.Response response = await http.get(dataURL);
      // Lots of JSON to parse
      replyTo.send(jsonDecode(response.body) as List<Map<String, dynamic>>);
    }
  }

  Future<List<Map<String, dynamic>>> sendReceive(SendPort port, String msg) {
    final ReceivePort response = ReceivePort();
    port.send(<dynamic>[msg, response.sendPort]);
    return response.first as Future<List<Map<String, dynamic>>>;
  }

  Widget getBody() {
    if (showLoadingDialog) {
      return getProgressDialog();
    }
    return getListView();
  }

  Widget getProgressDialog() {
    return const Center(child: CircularProgressIndicator());
  }

  ListView getListView() {
    return ListView.builder(
      itemCount: data.length,
      itemBuilder: (context, index) {
        return getRow(index);
      },
    );
  }

  Widget getRow(int index) {
    return Padding(
      padding: const EdgeInsets.all(10),
      child: Text('Row ${data[index]['title']}'),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: getBody(),
    );
  }
}

In Xamarin.Forms you would use HttpClient. Making a network call in Flutter is easy when you use the popular http package. This abstracts away a lot of the networking that you might normally implement yourself, making it simple to make network calls.

To use the http package, add it to your dependencies in pubspec.yaml:

dependencies:
  http: ^1.1.0

To make a network request, call await on the async function http.get():

Future<void> loadData() async {
  final Uri dataURL = Uri.parse(
    'https://jsonplaceholder.typicode.com/posts',
  );
  final http.Response response = await http.get(dataURL);
  setState(() {
    data = jsonDecode(response.body);
  });
}

In Xamarin.Forms you would typically create a loading indicator, either directly in XAML or through a 3rd party plugin such as AcrDialogs.

In Flutter, use a ProgressIndicator widget. Show the progress programmatically by controlling when it's rendered through a boolean flag. Tell Flutter to update its state before your long-running task starts, and hide it after it ends.

In the example below, the build function is separated into three different functions. If showLoadingDialog is true (when widgets.length == 0), then render the ProgressIndicator. Otherwise, render the ListView with the data returned from a network call.

import 'dart:async';
import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List<Map<String, dynamic>> data = <Map<String, dynamic>>[];

  @override
  void initState() {
    super.initState();
    loadData();
  }

  bool get showLoadingDialog => data.isEmpty;

  Future<void> loadData() async {
    final Uri dataURL = Uri.parse(
      'https://jsonplaceholder.typicode.com/posts',
    );
    final http.Response response = await http.get(dataURL);
    setState(() {
      data = jsonDecode(response.body);
    });
  }

  Widget getBody() {
    if (showLoadingDialog) {
      return getProgressDialog();
    }
    return getListView();
  }

  Widget getProgressDialog() {
    return const Center(child: CircularProgressIndicator());
  }

  ListView getListView() {
    return ListView.builder(
      itemCount: data.length,
      itemBuilder: (context, index) {
        return getRow(index);
      },
    );
  }

  Widget getRow(int index) {
    return Padding(
      padding: const EdgeInsets.all(10),
      child: Text('Row ${data[index]['title']}'),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: getBody(),
    );
  }
}

Xamarin.Forms has no platform independent way of storing images, you had to place images in the iOS xcasset folder, or on Android in the various drawable folders.

While Android and iOS treat resources and assets as distinct items, Flutter apps have only assets. All resources that would live in the Resources/drawable-* folders on Android, are placed in an assets' folder for Flutter.

Flutter follows a simple density-based format like iOS. Assets might be 1.0x, 2.0x, 3.0x, or any other multiplier. Flutter doesn't have dps but there are logical pixels, which are basically the same as device-independent pixels. Flutter's devicePixelRatio expresses the ratio of physical pixels in a single logical pixel.

The equivalent to Android's density buckets are:

Assets are located in any arbitrary folder— Flutter has no predefined folder structure. You declare the assets (with location) in the pubspec.yaml file, and Flutter picks them up.

To add a new image asset called my_icon.png to our Flutter project, for example, and deciding that it should live in a folder we arbitrarily called images, you would put the base image (1.0x) in the images folder, and all the other variants in sub-folders called with the appropriate ratio multiplier:

images/my_icon.png       // Base: 1.0x image
images/2.0x/my_icon.png  // 2.0x image
images/3.0x/my_icon.png  // 3.0x image

Next, you'll need to declare these images in your pubspec.yaml file:

assets:
 - images/my_icon.jpeg

You can directly access your images in an Image.asset widget:

@override
Widget build(BuildContext context) {
  return Image.asset('images/my_icon.png');
}

or using AssetImage:

@override
Widget build(BuildContext context) {
  return const Image(
    image: AssetImage('images/my_image.png'),
  );
}

More detailed information can be found in Adding assets and images.

Unlike .NET which has resx files, Flutter doesn't currently have a dedicated system for handling strings. At the moment, the best practice is to declare your copy text in a class as static fields and access them from there. For example:

class Strings {
  static const String welcomeMessage = 'Welcome To Flutter';
}

You can access your strings as such:

Text(Strings.welcomeMessage);

By default, Flutter only supports US English for its strings. If you need to add support for other languages, include the flutter_localizations package. You might also need to add Dart's intl package to use i10n machinery, such as date/time formatting.

dependencies:
  flutter_localizations:
    sdk: flutter
  intl: any # Use version of intl from flutter_localizations.

To use the flutter_localizations package, specify the localizationsDelegates and supportedLocales on the app widget:

import 'package:flutter_localizations/flutter_localizations.dart';

class MyWidget extends StatelessWidget {
  const MyWidget({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      localizationsDelegates: <LocalizationsDelegate<dynamic>>[
        // Add app-specific localization delegate[s] here
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],
      supportedLocales: <Locale>[
        Locale('en', 'US'), // English
        Locale('he', 'IL'), // Hebrew
        // ... other locales the app supports
      ],
    );
  }
}

The delegates contain the actual localized values, while the supportedLocales defines which locales the app supports. The above example uses a MaterialApp, so it has both a GlobalWidgetsLocalizations for the base widgets localized values, and a MaterialWidgetsLocalizations for the Material widgets localizations. If you use WidgetsApp for your app, you don't need the latter. Note that these two delegates contain "default" values, but you'll need to provide one or more delegates for your own app's localizable copy, if you want those to be localized too.

When initialized, the WidgetsApp (or MaterialApp) creates a Localizations widget for you, with the delegates you specify. The current locale for the device is always accessible from the Localizations widget from the current context (in the form of a Locale object), or using the Window.locale.

To access localized resources, use the Localizations.of() method to access a specific localizations class that is provided by a given delegate. Use the intl_translation package to extract translatable copy to arb files for translating, and importing them back into the app for using them with intl.

For further details on internationalization and localization in Flutter, see the internationalization guide, which has sample code with and without the intl package.

In Xamarin.Forms you will have a csproj file. The closest equivalent in Flutter is pubspec.yaml, which contains package dependencies and various project details. Similar to .NET Standard, files within the same directory are considered part of the project.

In the .NET ecosystem, native Xamarin projects and Xamarin.Forms projects had access to Nuget and the built-in package management system. Flutter apps contain a native Android app, native iOS app and Flutter app.

In Android, you add dependencies by adding to your Gradle build script. In iOS, you add dependencies by adding to your Podfile.

Flutter uses Dart's own build system, and the Pub package manager. The tools delegate the building of the native Android and iOS wrapper apps to the respective build systems.

In general, use pubspec.yaml to declare external dependencies to use in Flutter. A good place to find Flutter packages is on pub.dev.

In Xamarin.Forms, you have an Application that contains OnStart, OnResume and OnSleep. In Flutter, you can instead listen to similar lifecycle events by hooking into the WidgetsBinding observer and listening to the didChangeAppLifecycleState() change event.

The observable lifecycle events are:

inactive

The application is in an inactive state and is not receiving user input. This event is iOS only.

paused

The application is not currently visible to the user, is not responding to user input, but is running in the background.

resumed

The application is visible and responding to user input.

suspending

The application is suspended momentarily. This event is Android only.

For more details on the meaning of these states, see the AppLifecycleStatus documentation.

In Xamarin.Forms you can create a StackLayout with an Orientation of horizontal or vertical. Flutter has a similar approach, however you would use the Row or Column widgets.

If you notice the two code samples are identical except the Row and Column widget. The children are the same and this feature can be exploited to develop rich layouts that can change overtime with the same children.

@override
Widget build(BuildContext context) {
  return const Row(
    mainAxisAlignment: MainAxisAlignment.center,
    children: <Widget>[
      Text('Row One'),
      Text('Row Two'),
      Text('Row Three'),
      Text('Row Four'),
    ],
  );
}

@override
Widget build(BuildContext context) {
  return const Column(
    mainAxisAlignment: MainAxisAlignment.center,
    children: <Widget>[
      Text('Column One'),
      Text('Column Two'),
      Text('Column Three'),
      Text('Column Four'),
    ],
  );

The closest equivalent of a Grid would be a GridView. This is much more powerful than what you are used to in Xamarin.Forms. A GridView provides automatic scrolling when the content exceeds its viewable space.

@override
Widget build(BuildContext context) {
  return GridView.count(
    // Create a grid with 2 columns. If you change the scrollDirection to
    // horizontal, this would produce 2 rows.
    crossAxisCount: 2,
    // Generate 100 widgets that display their index in the list.
    children: List<Widget>.generate(
      100,
      (index) {
        return Center(
          child: Text(
            'Item $index',
            style: Theme.of(context).textTheme.headlineMedium,
          ),
        );
      },
    ),
  );
}

You might have used a Grid in Xamarin.Forms to implement widgets that overlay other widgets. In Flutter, you accomplish this with the Stack widget.

This sample creates two icons that overlap each other.

@override
Widget build(BuildContext context) {
  return const Stack(
    children: <Widget>[
      Icon(
        Icons.add_box,
        size: 24,
        color: Colors.black,
      ),
      Positioned(
        left: 10,
        child: Icon(
          Icons.add_circle,
          size: 24,
          color: Colors.black,
        ),
      ),
    ],
  );
}

In Xamarin.Forms, a ScrollView wraps around a VisualElement, and if the content is larger than the device screen, it scrolls.

In Flutter, the closest match is the SingleChildScrollView widget. You simply fill the Widget with the content that you want to be scrollable.

@override
Widget build(BuildContext context) {
  return const SingleChildScrollView(
    child: Text('Long Content'),
  );
}

If you have many items you want to wrap in a scroll, even of different Widget types, you might want to use a ListView. This might seem like overkill, but in Flutter this is far more optimized and less intensive than a Xamarin.Forms ListView, which is backing on to platform specific controls.

@override
Widget build(BuildContext context) {
  return ListView(
    children: const <Widget>[
      Text('Row One'),
      Text('Row Two'),
      Text('Row Three'),
      Text('Row Four'),
    ],
  );
}

Landscape transitions can be handled automatically by setting the configChanges property in the AndroidManifest.xml:

<activity android:configChanges="orientation|screenSize" />

In Xamarin.Forms, Elements might contain a click event you can attach to. Many elements also contain a Command that is tied to this event. Alternatively you would use the TapGestureRecognizer. In Flutter there are two very similar ways:

1. If the widget supports event detection, pass a function to it and handle it in the function. For example, the ElevatedButton has an onPressed parameter:

   dart

   @override
   Widget build(BuildContext context) {
     return ElevatedButton(
       onPressed: () {
         developer.log('click');
       },
       child: const Text('Button'),
     );
   }

2. If the widget doesn't support event detection, wrap the widget in a GestureDetector and pass a function to the onTap parameter.

   dart

   class SampleApp extends StatelessWidget {
     const SampleApp({super.key});
   
     @override
     Widget build(BuildContext context) {
       return Scaffold(
         body: Center(
           child: GestureDetector(
             onTap: () {
               developer.log('tap');
             },
             child: const FlutterLogo(size: 200),
           ),
         ),
       );
     }
   }

In Xamarin.Forms you would add a GestureRecognizer to the View. You would normally be limited to TapGestureRecognizer, PinchGestureRecognizer, PanGestureRecognizer, SwipeGestureRecognizer, DragGestureRecognizer and DropGestureRecognizer unless you built your own.

In Flutter, using the GestureDetector, you can listen to a wide range of Gestures such as:

• Tap

onTapDown

A pointer that might cause a tap has contacted the screen at a particular location.

onTapUp

A pointer that triggers a tap has stopped contacting the screen at a particular location.

onTap

A tap has occurred.

onTapCancel

The pointer that previously triggered the onTapDown won't cause a tap.

• Double tap

onDoubleTap

The user tapped the screen at the same location twice in quick succession.

• Long press

onLongPress

A pointer has remained in contact with the screen at the same location for a long period of time.

• Vertical drag

onVerticalDragStart

A pointer has contacted the screen and might begin to move vertically.

onVerticalDragUpdate

A pointer in contact with the screen has moved further in the vertical direction.

onVerticalDragEnd

A pointer that was previously in contact with the screen and moving vertically is no longer in contact with the screen and was moving at a specific velocity when it stopped contacting the screen.

• Horizontal drag

onHorizontalDragStart

A pointer has contacted the screen and might begin to move horizontally.

onHorizontalDragUpdate

A pointer in contact with the screen has moved further in the horizontal direction.

onHorizontalDragEnd

A pointer that was previously in contact with the screen and moving horizontally is no longer in contact with the screen and was moving at a specific velocity when it stopped contacting the screen.

The following example shows a GestureDetector that rotates the Flutter logo on a double tap:

class RotatingFlutterDetector extends StatefulWidget {
  const RotatingFlutterDetector({super.key});

  @override
  State<RotatingFlutterDetector> createState() =>
      _RotatingFlutterDetectorState();
}

class _RotatingFlutterDetectorState extends State<RotatingFlutterDetector>
    with SingleTickerProviderStateMixin {
  late final AnimationController controller;
  late final CurvedAnimation curve;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      duration: const Duration(milliseconds: 2000),
      vsync: this,
    );
    curve = CurvedAnimation(parent: controller, curve: Curves.easeIn);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: GestureDetector(
          onDoubleTap: () {
            if (controller.isCompleted) {
              controller.reverse();
            } else {
              controller.forward();
            }
          },
          child: RotationTransition(
            turns: curve,
            child: const FlutterLogo(size: 200),
          ),
        ),
      ),
    );
  }
}

The equivalent to a ListView in Flutter is … a ListView!

In a Xamarin.Forms ListView, you create a ViewCell and possibly a DataTemplateSelectorand pass it into the ListView, which renders each row with what your DataTemplateSelector or ViewCell returns. However, you often have to make sure you turn on Cell Recycling otherwise you will run into memory issues and slow scrolling speeds.

Due to Flutter's immutable widget pattern, you pass a list of widgets to your ListView, and Flutter takes care of making sure that scrolling is fast and smooth.

import 'package:flutter/material.dart';

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  /// This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatelessWidget {
  const SampleAppPage({super.key});

  List<Widget> _getListData() {
    return List<Widget>.generate(
      100,
      (index) => Padding(
        padding: const EdgeInsets.all(10),
        child: Text('Row $index'),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: ListView(children: _getListData()),
    );
  }
}

In Xamarin.Forms, the ListView has an ItemTapped method to find out which item was clicked. There are many other techniques you might have used such as checking when SelectedItem or EventToCommand behaviors change.

In Flutter, use the touch handling provided by the passed-in widgets.

import 'dart:developer' as developer;
import 'package:flutter/material.dart';

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  // This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List<Widget> _getListData() {
    return List<Widget>.generate(
      100,
      (index) => GestureDetector(
        onTap: () {
          developer.log('Row $index tapped');
        },
        child: Padding(
          padding: const EdgeInsets.all(10),
          child: Text('Row $index'),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: ListView(children: _getListData()),
    );
  }
}

In Xamarin.Forms, if you bound the ItemsSource property to an ObservableCollection, you would just update the list in your ViewModel. Alternatively, you could assign a new List to the ItemSource property.

In Flutter, things work a little differently. If you update the list of widgets inside a setState() method, you would quickly see that your data did not change visually. This is because when setState() is called, the Flutter rendering engine looks at the widget tree to see if anything has changed. When it gets to your ListView, it performs a == check, and determines that the two ListViews are the same. Nothing has changed, so no update is required.

For a simple way to update your ListView, create a new List inside of setState(), and copy the data from the old list to the new list. While this approach is simple, it is not recommended for large data sets, as shown in the next example.

import 'dart:developer' as developer;
import 'package:flutter/material.dart';

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  /// This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List<Widget> widgets = <Widget>[];

  @override
  void initState() {
    super.initState();
    for (int i = 0; i < 100; i++) {
      widgets.add(getRow(i));
    }
  }

  Widget getRow(int index) {
    return GestureDetector(
      onTap: () {
        setState(() {
          widgets = List<Widget>.from(widgets);
          widgets.add(getRow(widgets.length));
          developer.log('Row $index');
        });
      },
      child: Padding(
        padding: const EdgeInsets.all(10),
        child: Text('Row $index'),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: ListView(children: widgets),
    );
  }
}

The recommended, efficient, and effective way to build a list uses a ListView.Builder. This method is great when you have a dynamic list or a list with very large amounts of data. This is essentially the equivalent of RecyclerView on Android, which automatically recycles list elements for you:

import 'dart:developer' as developer;
import 'package:flutter/material.dart';

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  /// This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List<Widget> widgets = [];

  @override
  void initState() {
    super.initState();
    for (int i = 0; i < 100; i++) {
      widgets.add(getRow(i));
    }
  }

  Widget getRow(int index) {
    return GestureDetector(
      onTap: () {
        setState(() {
          widgets.add(getRow(widgets.length));
          developer.log('Row $index');
        });
      },
      child: Padding(
        padding: const EdgeInsets.all(10),
        child: Text('Row $index'),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: ListView.builder(
        itemCount: widgets.length,
        itemBuilder: (context, index) {
          return getRow(index);
        },
      ),
    );
  }
}

Instead of creating a ListView, create a ListView.builder that takes two key parameters: the initial length of the list, and an item builder function.

The item builder function is similar to the getView function in an Android adapter; it takes a position, and returns the row you want rendered at that position.

Finally, but most importantly, notice that the onTap() function doesn't recreate the list anymore, but instead adds to it.

For more information, see Your first Flutter app codelab.

In Xamarin.Forms, you would have to add a custom font in each native project. Then, in your Element you would assign this font name to the FontFamily attribute using filename#fontname and just fontname for iOS.

In Flutter, place the font file in a folder and reference it in the pubspec.yaml file, similar to how you import images.

fonts:
  - family: MyCustomFont
    fonts:
      - asset: fonts/MyCustomFont.ttf
      - style: italic

Then assign the font to your Text widget:

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(title: const Text('Sample App')),
    body: const Center(
      child: Text(
        'This is a custom font text',
        style: TextStyle(fontFamily: 'MyCustomFont'),
      ),
    ),
  );
}

Along with fonts, you can customize other styling elements on a Text widget. The style parameter of a Text widget takes a TextStyle object, where you can customize many parameters, such as:

• color
• decoration
• decorationColor
• decorationStyle
• fontFamily
• fontSize
• fontStyle
• fontWeight
• hashCode
• height
• inherit
• letterSpacing
• textBaseline
• wordSpacing

Xamarin.Forms elements allow you to directly query the element to determine the state of its properties, or whether it's bound to a property in a ViewModel.

Retrieving information in Flutter is handled by specialized widgets and is different from how you are used to. If you have a TextFieldor a TextFormField, you can supply a TextEditingController to retrieve user input:

import 'package:flutter/material.dart';

class MyForm extends StatefulWidget {
  const MyForm({super.key});

  @override
  State<MyForm> createState() => _MyFormState();
}

class _MyFormState extends State<MyForm> {
  /// Create a text controller and use it to retrieve the current value
  /// of the TextField.
  final TextEditingController myController = TextEditingController();

  @override
  void dispose() {
    // Clean up the controller when disposing of the widget.
    myController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Retrieve Text Input')),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: TextField(controller: myController),
      ),
      floatingActionButton: FloatingActionButton(
        // When the user presses the button, show an alert dialog with the
        // text that the user has typed into our text field.
        onPressed: () {
          showDialog(
            context: context,
            builder: (context) {
              return AlertDialog(
                // Retrieve the text that the user has entered using the
                // TextEditingController.
                content: Text(myController.text),
              );
            },
          );
        },
        tooltip: 'Show me the value!',
        child: const Icon(Icons.text_fields),
      ),
    );
  }
}

You can find more information and the full code listing in Retrieve the value of a text field, from the Flutter cookbook.

In Xamarin.Forms, some Elements support a Placeholder property that you can assign a value to. For example:

<Entry Placeholder="This is a hint">

In Flutter, you can easily show a "hint" or a placeholder text for your input by adding an InputDecoration object to the decoration constructor parameter for the text widget.

TextField(
  decoration: InputDecoration(hintText: 'This is a hint'),
),

With Xamarin.Forms, if you wished to provide a visual hint of a validation error, you would need to create new properties and VisualElements surrounding the Elements that had validation errors.

In Flutter, you pass through an InputDecoration object to the decoration constructor for the text widget.

However, you don't want to start off by showing an error. Instead, when the user has entered invalid data, update the state, and pass a new InputDecoration object.

import 'package:flutter/material.dart';

void main() {
  runApp(const SampleApp());
}

class SampleApp extends StatelessWidget {
  /// This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Sample App',
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  const SampleAppPage({super.key});

  @override
  State<SampleAppPage> createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  String? _errorText;

  String? _getErrorText() {
    return _errorText;
  }

  bool isEmail(String em) {
    const String emailRegexp =
        r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|'
        r'(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|'
        r'(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$';
    final RegExp regExp = RegExp(emailRegexp);
    return regExp.hasMatch(em);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Sample App')),
      body: Center(
        child: TextField(
          onSubmitted: (text) {
            setState(() {
              if (!isEmail(text)) {
                _errorText = 'Error: This is not an email';
              } else {
                _errorText = null;
              }
            });
          },
          decoration: InputDecoration(
            hintText: 'This is a hint',
            errorText: _getErrorText(),
          ),
        ),
      ),
    );
  }
}

Flutter doesn't run code directly on the underlying platform; rather, the Dart code that makes up a Flutter app is run natively on the device, "sidestepping" the SDK provided by the platform. That means, for example, when you perform a network request in Dart, it runs directly in the Dart context. You don't use the Android or iOS APIs you normally take advantage of when writing native apps. Your Flutter app is still hosted in a native app's ViewController or Activity as a view, but you don't have direct access to this, or the native framework.

This doesn't mean Flutter apps can't interact with those native APIs, or with any native code you have. Flutter provides platform channels that communicate and exchange data with the ViewController or Activity that hosts your Flutter view. Platform channels are essentially an asynchronous messaging mechanism that bridges the Dart code with the host ViewController or Activity and the iOS or Android framework it runs on. You can use platform channels to execute a method on the native side, or to retrieve some data from the device's sensors, for example.

In addition to directly using platform channels, you can use a variety of pre-made plugins that encapsulate the native and Dart code for a specific goal. For example, you can use a plugin to access the camera roll and the device camera directly from Flutter, without having to write your own integration. Plugins are found on pub.dev, Dart and Flutter's open source package repository. Some packages might support native integrations on iOS, or Android, or both.

If you can't find a plugin on pub.dev that fits your needs, you can write your own, and publish it on pub.dev.

Use the geolocator community plugin.

The camera plugin is popular for accessing the camera.

To log in with Facebook, use the flutter_facebook_login community plugin.

Most Firebase functions are covered by first party plugins. These plugins are first-party integrations, maintained by the Flutter team:

• google_mobile_ads for Google Mobile Ads for Flutter
• firebase_analytics for Firebase Analytics
• firebase_auth for Firebase Auth
• firebase_database for Firebase RTDB
• firebase_storage for Firebase Cloud Storage
• firebase_messaging for Firebase Messaging (FCM)
• flutter_firebase_ui for quick Firebase Auth integrations (Facebook, Google, Twitter and email)
• cloud_firestore for Firebase Cloud Firestore

You can also find some third-party Firebase plugins on pub.dev that cover areas not directly covered by the first-party plugins.

If there is platform-specific functionality that Flutter or its community plugins are missing, you can build your own following the developing packages and plugins page.

Flutter's plugin architecture, in a nutshell, is much like using an Event bus in Android: you fire off a message and let the receiver process and emit a result back to you. In this case, the receiver is code running on the native side on Android or iOS.

Flutter comes with a beautiful, built-in implementation of Material Design, which handles much of the styling and theming needs that you would typically do.

Xamarin.Forms does have a global ResourceDictionary where you can share styles across your app. Alternatively, there is Theme support currently in preview.

In Flutter, you declare themes in the top level widget.

To take full advantage of Material Components in your app, you can declare a top level widget MaterialApp as the entry point to your application. MaterialApp is a convenience widget that wraps a number of widgets that are commonly required for applications implementing Material Design. It builds upon a WidgetsApp by adding Material-specific functionality.

You can also use a WidgetsApp as your app widget, which provides some of the same functionality, but is not as rich as MaterialApp.

To customize the colors and styles of any child components, pass a ThemeData object to the MaterialApp widget. For example, in the following code, the color scheme from seed is set to deepPurple and text selection color is red.

class SampleApp extends StatelessWidget {
  /// This widget is the root of your application.
  const SampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Sample App',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        textSelectionTheme:
            const TextSelectionThemeData(selectionColor: Colors.red),
      ),
      home: const SampleAppPage(),
    );
  }
}

Xamarin.Forms developers will likely be familiar with the Xam.Plugins.Settings plugin.

In Flutter, access equivalent functionality using the shared_preferences plugin. This plugin wraps the functionality of both UserDefaults and the Android equivalent, SharedPreferences.

In Xamarin.Forms most applications would use the sqlite-net-pcl plugin to access SQLite databases.

In Flutter, on macOS, Android, and iOS, access this functionality using the sqflite plugin.

Use the DevTools suite for debugging Flutter or Dart apps.

DevTools includes support for profiling, examining the heap, inspecting the widget tree, logging diagnostics, debugging, observing executed lines of code, debugging memory leaks and memory fragmentation. For more information, check out the DevTools documentation.

In Android, you use Firebase Cloud Messaging to set up push notifications for your app.

In Flutter, access this functionality using the firebase_messaging plugin. For more information on using the Firebase Cloud Messaging API, see the firebase_messaging plugin documentation.