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Animating a Widget across screens

It’s often helpful to guide users through our apps as they navigate from screen to screen. A common technique to lead users through an app is to animate a Widget from one screen to the next. This creates a visual anchor connecting the two screens.

How can we animate a Widget from one screen to the next with Flutter? Using the Hero Widget!

Directions

  1. Create two screens showing the same image
  2. Add a Hero Widget to the first screen
  3. Add a Hero Widget to the second screen

1. Create two screens showing the same image

In this example, we’ll display the same image on both screens. We’ll want to animate the image from the first screen to the second screen when the user taps on the image. For now, we’ll create the visual structure, and handle animations in the next steps!

Note: This example builds upon the Navigate to a new screen and back and Handling Taps recipes.

class MainScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Main Screen'),
      ),
      body: new GestureDetector(
        onTap: () {
          Navigator.push(context, new MaterialPageRoute(builder: (_) {
            return new DetailScreen();
          }));
        },
        child: new Image.network(
          'https://raw.githubusercontent.com/flutter/website/master/_includes/code/layout/lakes/images/lake.jpg',
        ),
      ),
    );
  }
}

class DetailScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new GestureDetector(
        onTap: () {
          Navigator.pop(context);
        },
        child: new Center(
          child: new Image.network(
            'https://raw.githubusercontent.com/flutter/website/master/_includes/code/layout/lakes/images/lake.jpg',
          ),
        ),
      ),
    );
  }
}

2. Add a Hero Widget to the first screen

In order to connect the two screens together with an animation, we need to wrap the Image Widget on both screens in a Hero Widget. The Hero Widget requires two arguments:

  1. tag: An object that identifies the Hero. It must be the same on both screens.
  2. child: The Widget we want to animate across screens.
new Hero(
  tag: 'imageHero',
  child: new Image.network(
    'https://raw.githubusercontent.com/flutter/website/master/_includes/code/layout/lakes/images/lake.jpg',
  ),
);

3. Add a Hero Widget to the second screen

To complete the connection with the first screen, we need to wrap the Image on the second screen with a Hero Widget as well! It must use the same tag as the first screen.

After you apply the Hero Widget to the second screen, the animation between screens will work!

new Hero(
  tag: 'imageHero',
  child: new Image.network(
    'https://raw.githubusercontent.com/flutter/website/master/_includes/code/layout/lakes/images/lake.jpg',
  ),
);

Note: this code is identical to what we had on the first screen! In general, you could create a reusable Widget instead of repeating code, but for this example, we’ll duplicate the code for demonstration purposes.

Complete Example

import 'package:flutter/material.dart';

void main() => runApp(new HeroApp());

class HeroApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Transition Demo',
      home: new MainScreen(),
    );
  }
}

class MainScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Main Screen'),
      ),
      body: new GestureDetector(
        child: new Hero(
          tag: 'imageHero',
          child: new Image.network(
            'https://raw.githubusercontent.com/flutter/website/master/_includes/code/layout/lakes/images/lake.jpg',
          ),
        ),
        onTap: () {
          Navigator.push(context, new MaterialPageRoute(builder: (_) {
            return new DetailScreen();
          }));
        },
      ),
    );
  }
}

class DetailScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new GestureDetector(
        child: new Center(
          child: new Hero(
            tag: 'imageHero',
            child: new Image.network(
              'https://raw.githubusercontent.com/flutter/website/master/_includes/code/layout/lakes/images/lake.jpg',
            ),
          ),
        ),
        onTap: () {
          Navigator.pop(context);
        },
      ),
    );
  }
}

Hero Demo