Return data from a screen

In some cases, we might want to return data from a new screen. For example, say we push a new screen that presents two options to a user. When the user taps on an option, we’ll want to inform our first screen of the user’s selection so it can act on that information!

How can we achieve this? Using Navigator.pop!

Directions

  1. Define the home screen
  2. Add a button that launches the selection screen
  3. Show the selection screen with two buttons
  4. When a button is tapped, close the selection screen
  5. Show a snackbar on the home screen with the selection

1. Define the home screen

The home screen will display a button. When tapped, it will launch the selection screen!

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Returning Data Demo'),
      ),
      // We'll create the SelectionButton Widget in the next step
      body: Center(child: SelectionButton()),
    );
  }
}

2. Add a button that launches the selection screen

Now, we’ll create our SelectionButton. Our selection button will:

  1. Launch the SelectionScreen when it’s tapped
  2. Wait for the SelectionScreen to return a result
class SelectionButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        _navigateAndDisplaySelection(context);
      },
      child: Text('Pick an option, any option!'),
    );
  }

  // A method that launches the SelectionScreen and awaits the result from
  // Navigator.pop
  _navigateAndDisplaySelection(BuildContext context) async {
    // Navigator.push returns a Future that will complete after we call
    // Navigator.pop on the Selection Screen!
    final result = await Navigator.push(
      context,
      // We'll create the SelectionScreen in the next step!
      MaterialPageRoute(builder: (context) => SelectionScreen()),
    );
  }
}

3. Show the selection screen with two buttons

Now, we’ll need to build a selection screen! It will contain two buttons. When a user taps on a button, it should close the selection screen and let the home screen know which button was tapped!

For now, we’ll define the UI, and figure out how to return data in the next step.

class SelectionScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Pick an option'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: RaisedButton(
                onPressed: () {
                  // Pop here with "Yep"...
                },
                child: Text('Yep!'),
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: RaisedButton(
                onPressed: () {
                  // Pop here with "Nope"
                },
                child: Text('Nope.'),
              ),
            )
          ],
        ),
      ),
    );
  }
}

4. When a button is tapped, close the selection screen

Now, we’ll want to update the onPressed callback for both of our buttons! In order to return data to the first screen, we’ll need to use the Navigator.pop method.

Navigator.pop accepts an optional second argument called result. If we provide a result, it will be returned to the Future in our SelectionButton!

Yep button

RaisedButton(
  onPressed: () {
    // Our Yep button will return "Yep!" as the result
    Navigator.pop(context, 'Yep!');
  },
  child: Text('Yep!'),
);

Nope button

RaisedButton(
  onPressed: () {
    // Our Nope button will return "Nope!" as the result
    Navigator.pop(context, 'Nope!');
  },
  child: Text('Nope!'),
);

5. Show a snackbar on the home screen with the selection

Now that we’re launching a selection screen and awaiting the result, we’ll want to do something with the information that’s returned!

In this case, we’ll show a Snackbar displaying the result. To do so, we’ll update the _navigateAndDisplaySelection method in our SelectionButton.

_navigateAndDisplaySelection(BuildContext context) async {
  final result = await Navigator.push(
    context,
    MaterialPageRoute(builder: (context) => SelectionScreen()),
  );

  // After the Selection Screen returns a result, show it in a Snackbar!
  Scaffold.of(context).showSnackBar(SnackBar(content: Text("$result")));
}

Complete example

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    title: 'Returning Data',
    home: HomeScreen(),
  ));
}

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Returning Data Demo'),
      ),
      body: Center(child: SelectionButton()),
    );
  }
}

class SelectionButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        _navigateAndDisplaySelection(context);
      },
      child: Text('Pick an option, any option!'),
    );
  }

  // A method that launches the SelectionScreen and awaits the result from
  // Navigator.pop!
  _navigateAndDisplaySelection(BuildContext context) async {
    // Navigator.push returns a Future that will complete after we call
    // Navigator.pop on the Selection Screen!
    final result = await Navigator.push(
      context,
      MaterialPageRoute(builder: (context) => SelectionScreen()),
    );

    // After the Selection Screen returns a result, show it in a Snackbar!
    Scaffold.of(context).showSnackBar(SnackBar(content: Text("$result")));
  }
}

class SelectionScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Pick an option'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: RaisedButton(
                onPressed: () {
                  // Close the screen and return "Yep!" as the result
                  Navigator.pop(context, 'Yep!');
                },
                child: Text('Yep!'),
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: RaisedButton(
                onPressed: () {
                  // Close the screen and return "Nope!" as the result
                  Navigator.pop(context, 'Nope.');
                },
                child: Text('Nope.'),
              ),
            )
          ],
        ),
      ),
    );
  }
}

Returning Data Demo