How to detect when an animation has ended in Flutter

In this Google flutter code example we are going to learn how to detect when an animation has ended in Flutter.

You can copy and adopt this source code example to your android project without reinventing the wheel.

The code is based on flutter version 1.

Main.dart (App entry point)

import 'package:flutter/material.dart';
import 'detect_end_of_animation_task-9.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: DetectEndOfAnimation(),
    );
  }
}

detect_end_of_animation_task-9.dart

import 'package:flutter/material.dart';

class DetectEndOfAnimation extends StatefulWidget {
  @override
  _DetectEndOfAnimationState createState() => _DetectEndOfAnimationState();
}

class _DetectEndOfAnimationState extends State<DetectEndOfAnimation>
    with SingleTickerProviderStateMixin {
  AnimationController animationController;
  Animation<double> animation;
  GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  void initState() {
    super.initState();
    animationController = AnimationController(
      vsync: this,
      duration: Duration(seconds: 5),
    )..addListener(() => setState(() {}));

    animation = Tween<double>(
      begin: 50.0,
      end: 120.0,
    ).animate(animationController);

    animationController.forward();

    animation.addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        scaffoldKey.currentState.showSnackBar(SnackBar(
          content: Text("Animation has ended"),
        ));
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: scaffoldKey,
      appBar: AppBar(title: Text("Detect End Of an Animation Example")),
      body: Center(
        child: Container(
          color: Colors.red,
          height: animation.value,
          width: animation.value,
        ),
      ),
    );
  }
}

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