Awesome

🎬 Simple Animations

Simple Animations simplifies the process of creating beautiful custom animations:

• Easily create custom animations in stateless widgets
• Animate multiple properties at once
• Create staggered animations within seconds
• Simplified working with AnimationController instances
• Debug animations

Table of Contents

Quickstart

• Animation Builder - Quickstart
• Movie Tween - Quickstart
• Animation Mixin - Quickstart
• Animation Developer Tools - Quickstart

Animation Builder

• Essential parts of the animation
• PlayAnimationBuilder
• LoopAnimationBuilder
• MirrorAnimationBuilder
• CustomAnimationBuilder

Movie Tween

• Basic usage pattern
• Scenes
• Animate properties
• Curves
• Extrapolation
• Use developer tools
• Animation duration

Animation Mixin

• Basic usage pattern
• Create multiple AnimationController

Shortcuts for AnimationController

Animation Developer Tools

• Basic usage pattern
• Features and tricks

Quickstart

Directly dive in and let the code speak for itself.

Animation Builder - Quickstart

Animation Builder are powerful widgets to easily create custom animations.

import 'dart:math';

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

class ResizeCubeAnimation extends StatelessWidget {
  const ResizeCubeAnimation({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // PlayAnimationBuilder plays animation once
    return PlayAnimationBuilder<double>(
      tween: Tween(begin: 100.0, end: 200.0), // 100.0 to 200.0
      duration: const Duration(seconds: 1), // for 1 second
      builder: (context, value, _) {
        return Container(
          width: value, // use animated value
          height: value,
          color: Colors.blue,
        );
      },
      onCompleted: () {
        // do something ...
      },
    );
  }
}

class RotatingBox extends StatelessWidget {
  const RotatingBox({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // LoopAnimationBuilder plays forever: from beginning to end
    return LoopAnimationBuilder<double>(
      tween: Tween(begin: 0.0, end: 2 * pi), // 0° to 360° (2π)
      duration: const Duration(seconds: 2), // for 2 seconds per iteration
      builder: (context, value, _) {
        return Transform.rotate(
          angle: value, // use value
          child: Container(color: Colors.blue, width: 100, height: 100),
        );
      },
    );
  }
}

class ColorFadeLoop extends StatelessWidget {
  const ColorFadeLoop({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // MirrorAnimationBuilder plays forever: alternating forward and backward
    return MirrorAnimationBuilder<Color?>(
      tween: ColorTween(begin: Colors.red, end: Colors.blue), // red to blue
      duration: const Duration(seconds: 5), // for 5 seconds per iteration
      builder: (context, value, _) {
        return Container(
          color: value, // use animated value
          width: 100,
          height: 100,
        );
      },
    );
  }
}

Read guide or watch examples.

Movie Tween - Quickstart

Movie Tween combines multiple tween into one, including timeline control and value extrapolation.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

// Simple staggered tween
final tween1 = MovieTween()
  ..tween('width', Tween(begin: 0.0, end: 100),
          duration: const Duration(milliseconds: 1500), curve: Curves.easeIn)
      .thenTween('width', Tween(begin: 100, end: 200),
          duration: const Duration(milliseconds: 750), curve: Curves.easeOut);

// Design tween by composing scenes
final tween2 = MovieTween()
  ..scene(
          begin: const Duration(milliseconds: 0),
          duration: const Duration(milliseconds: 500))
      .tween('width', Tween<double>(begin: 0.0, end: 400.0))
      .tween('height', Tween<double>(begin: 500.0, end: 200.0))
      .tween('color', ColorTween(begin: Colors.red, end: Colors.blue))
  ..scene(
          begin: const Duration(milliseconds: 700),
          end: const Duration(milliseconds: 1200))
      .tween('width', Tween<double>(begin: 400.0, end: 500.0));

// Type-safe alternative
final width = MovieTweenProperty<double>();
final color = MovieTweenProperty<Color?>();

final tween3 = MovieTween()
  ..tween<double>(width, Tween(begin: 0.0, end: 100))
  ..tween<Color?>(color, ColorTween(begin: Colors.red, end: Colors.blue));

Read guide or watch examples.

Animation Mixin - Quickstart

The Animation Mixin manages AnimationController instances for you. No more boilerplate code.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

class MyWidget extends StatefulWidget {
  const MyWidget({Key? key}) : super(key: key);

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

// Add AnimationMixin
class _MyWidgetState extends State<MyWidget> with AnimationMixin {
  late Animation<double> size;

  @override
  void initState() {
    // The AnimationController instance `controller` is already wired up.
    // Just connect with it with the tweens.
    size = Tween<double>(begin: 0.0, end: 200.0).animate(controller);

    controller.play(); // start the animation playback

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      width: size.value, // use animated value
      height: size.value,
      color: Colors.red,
    );
  }
}

Read guide or watch examples.

Animation Developer Tools - Quickstart

Helps you fine tuning the animation. It allows you to pause anywhere, scroll around, speed up, slow down or focus on a certain part of the animation.

Read guide

Animation Builder

Animation Builder enables developers to craft custom animations with simple widgets.

Essential parts of the animation

You need three things to create an animation:

• tween: What value is changing within the animation?
• duration: How long does the animation take?
• builder: How does the UI look like regarding the changing value?

Tween

The tween is the description of your animation. Mostly it will change a value from A to B. Tweens describe what will happen but not how fast it will happen.

import 'package:flutter/material.dart';

// Animate a color from red to blue
var colorTween = ColorTween(begin: Colors.red, end: Colors.blue);

// Animate a double value from 0 to 100
var doubleTween = Tween<double>(begin: 0.0, end: 100.0);

To animate multiple properties, use a Movie Tween.

Duration

The duration is the time the animation takes.

Builder

The builder is a function that is called for each new rendered frame of your animation. It takes three parameters: context, value and child.

• context is your Flutter BuildContext

• value is current value of any animated variable, produced by the tween. If your tween is Tween<double>(begin: 0.0, end: 100.0), the value is a double somewhere between 0.0 and 100.0.

• child can be a widget that you might pass in a Animation Builder widget. This widget stays constant and is not affected by the animation.

How often the builder function is called, depends on the animation duration, and the framerate of the device used.

PlayAnimationBuilder

The PlayAnimationBuilder is a widget that plays an animation once.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

// Use type `Color?` because ColorTween produces type `Color?`
var widget = PlayAnimationBuilder<Color?>(
  tween: ColorTween(begin: Colors.red, end: Colors.blue), // define tween
  duration: const Duration(seconds: 5), // define duration
  builder: (context, value, _) {
    return Container(
      color: value, // use animated color
      width: 100,
      height: 100,
    );
  },
);

Delay

By default, animations will play automatically. You can set a delay to make PlayAnimationBuilder wait for a given amount of time.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = PlayAnimationBuilder<Color?>(
  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  delay: const Duration(seconds: 2), // add delay
  builder: (context, value, _) {
    return Container(
      color: value,
      width: 100,
      height: 100,
    );
  },
);

Non-linear motion

You can make your animation more appealing by applying non-linear motion behavior to it. Just pass a curve into the widget.

Flutter comes with a set of predefined curves inside the Curves class.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = PlayAnimationBuilder<Color?>(
  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  curve: Curves.easeInOut, // specify curve
  builder: (context, value, _) {
    return Container(
      color: value,
      width: 100,
      height: 100,
    );
  },
);

Animation lifecycle

You can react to the animation status by setting callbacks.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = PlayAnimationBuilder<Color?>(
  // lifecycle callbacks
  onStarted: () => debugPrint('Animation started'),
  onCompleted: () => debugPrint('Animation complete'),

  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  builder: (context, value, _) =>
      Container(color: value, width: 100, height: 100),
);

Using child widgets

Parts of the UI that are not effected by the animated value can be passed as a Widget into the child property. That Widget is available within the builder function. They will not rebuild when animated value changes and therefore has a positive performance impact.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = PlayAnimationBuilder<Color?>(
  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  // child gets passed into builder function
  builder: (context, value, child) {
    return Container(
      color: value,
      width: 100,
      height: 100,
      child: child, // use child
    );
  },
  child: const Text('Hello World'), // specify child widget
);

Using keys

If Flutter swaps out a PlayAnimationBuilder with another different PlayAnimationBuilder in a rebuild, it may recycle the first one. This may lead to a undesired behavior. In such a case use the key property.

You may watch this introduction to Key.

App example

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

void main() => runApp(
    const MaterialApp(home: Scaffold(body: Center(child: AnimatedGreenBox()))));

class AnimatedGreenBox extends StatelessWidget {
  const AnimatedGreenBox({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return PlayAnimationBuilder<double>(
      // specify tween (from 50.0 to 200.0)
      tween: Tween<double>(begin: 50.0, end: 200.0),

      // set a duration
      duration: const Duration(seconds: 5),

      // set a curve
      curve: Curves.easeInOut,

      // use builder function
      builder: (context, value, child) {
        // apply animated value obtained from builder function parameter
        return Container(
          width: value,
          height: value,
          color: Colors.green,
          child: child,
        );
      },
      child: const Text('Hello World'),
    );
  }
}

LoopAnimationBuilder

A LoopAnimationBuilder repeatedly plays the animation from the start to the end over and over again.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = LoopAnimationBuilder<Color?>(
  // mandatory parameters
  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  builder: (context, value, child) {
    return Container(color: value, width: 100, height: 100, child: child);
  },
  // optional parameters
  curve: Curves.easeInOut,
  child: const Text('Hello World'),
);

MirrorAnimationBuilder

A MirrorAnimationBuilder repeatedly plays the animation from the start to the end, then reverse to the start, then again forward and so on.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = MirrorAnimationBuilder<Color?>(
  // mandatory parameters
  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  builder: (context, value, child) {
    return Container(color: value, width: 100, height: 100, child: child);
  },
  // optional parameters
  curve: Curves.easeInOut,
  child: const Text('Hello World'),
);

CustomAnimationBuilder

Use CustomAnimationBuilder if the animation widgets discussed above aren't sufficient for you use case. Beside all parameters mentioned for PlayAnimationBuilder it allows you actively control the animation.

Control the animation

The control parameter can be set to the following values:

You can bind the control value to state variable and change it during the animation. The CustomAnimationBuilder will adapt to that.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

void main() => runApp(
    const MaterialApp(home: Scaffold(body: Center(child: SwappingButton()))));

class SwappingButton extends StatefulWidget {
  const SwappingButton({Key? key}) : super(key: key);

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

class _SwappingButtonState extends State<SwappingButton> {
  var control = Control.play; // define variable

  void _toggleDirection() {
    setState(() {
      // let the animation play to the opposite direction
      control = control == Control.play ? Control.playReverse : Control.play;
    });
  }

  @override
  Widget build(BuildContext context) {
    return CustomAnimationBuilder<double>(
      control: control, // bind variable with control instruction
      tween: Tween<double>(begin: -100.0, end: 100.0),
      duration: const Duration(seconds: 1),
      builder: (context, value, child) {
        // moves child from left to right
        return Transform.translate(
          offset: Offset(value, 0),
          child: child,
        );
      },
      child: OutlinedButton(
        // clicking button changes animation direction
        onPressed: _toggleDirection,
        child: const Text('Swap'),
      ),
    );
  }
}

Start position

By default the animation starts from the beginning (0.0). You can change this by setting the startPosition parameter. It can be set to a value between 0.0 (beginning) and 1.0 (end).

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = CustomAnimationBuilder<Color?>(
  control: Control.play,
  startPosition: 0.5, // set start position at 50%
  duration: const Duration(seconds: 5),
  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  builder: (context, value, child) {
    return Container(color: value, width: 100, height: 100);
  },
);

Animation lifecycle

You can react to the animation status by setting callbacks.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = CustomAnimationBuilder<Color?>(
  // lifecycle callbacks
  onStarted: () => debugPrint('Animation started'),
  onCompleted: () => debugPrint('Animation complete'),

  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  builder: (context, value, child) {
    return Container(color: value, width: 100, height: 100);
  },
);

It's also possible to directly access the AnimationStatusListener of the internal AnimationController.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

var widget = CustomAnimationBuilder<Color?>(
  animationStatusListener: (AnimationStatus status) {
    // provide listener
    if (status == AnimationStatus.completed) {
      debugPrint('Animation completed!');
    }
  },
  tween: ColorTween(begin: Colors.red, end: Colors.blue),
  duration: const Duration(seconds: 5),
  builder: (context, value, child) {
    return Container(color: value, width: 100, height: 100);
  },
);

Movie Tween

Movie Tween combines multiple tween into one, including timeline control and value extrapolation.

Basic usage pattern

Create a new MovieTween and use the tween() to tween multiples values:

final tween = MovieTween();

tween.tween('width', Tween(begin: 0.0, end: 100.0),
    duration: const Duration(milliseconds: 700));

tween.tween('height', Tween(begin: 100.0, end: 200.0),
    duration: const Duration(milliseconds: 700));

You can use .. to get a nice builder style syntax:

final tween = MovieTween()
  ..tween('width', Tween(begin: 0.0, end: 100.0),
      duration: const Duration(milliseconds: 700))
  ..tween('height', Tween(begin: 100.0, end: 200.0),
      duration: const Duration(milliseconds: 700));

In order to not repeat yourself, you can use scene() to create an explicit scene and apply both tween to it:

final tween = MovieTween();

tween.scene(duration: const Duration(milliseconds: 700))
  ..tween('width', Tween(begin: 0.0, end: 100.0))
  ..tween('height', Tween(begin: 100.0, end: 200.0));

Calling tween() creates a scene as well. Therefore you can just call thenTween() to create staggered animations.

final tween = MovieTween();

tween
    .tween('width', Tween(begin: 0.0, end: 100.0),
        duration: const Duration(milliseconds: 700))
    .thenTween('width', Tween(begin: 100.0, end: 200.0),
        duration: const Duration(milliseconds: 500));

You can use e.g. a PlayAnimationBuilder to bring the MovieTween alive:

@override
Widget build(BuildContext context) {
  // create tween
  var tween = MovieTween()
    ..scene(duration: const Duration(milliseconds: 700))
        .tween('width', Tween<double>(begin: 0.0, end: 100.0))
        .tween('height', Tween<double>(begin: 300.0, end: 200.0));

  return PlayAnimationBuilder<Movie>(
    tween: tween, // provide tween
    duration: tween.duration, // total duration obtained from MovieTween
    builder: (context, value, _) {
      return Container(
        width: value.get('width'), // get animated width value
        height: value.get('height'), // get animated height value
        color: Colors.yellow,
      );
    },
  );
}

MovieTween animates to Movie that offers you a get() method to obtain a single animated value.

Scenes

A MovieTween can consist of multiple scenes with each scene having multiple tweened properties. Those scenes can be created

• implicitly using tween() or thenTween(),
• explicitly using scene() or thenFor().

final tween = MovieTween();

// implicit scenes
final sceneA1 = tween.tween('x', Tween(begin: 0.0, end: 1.0),
    duration: const Duration(milliseconds: 700));

final sceneA2 = sceneA1.thenTween('x', Tween(begin: 1.0, end: 2.0),
    duration: const Duration(milliseconds: 500));

// explicit scenes
final sceneB1 = tween
    .scene(duration: const Duration(milliseconds: 700))
    .tween('x', Tween(begin: 0.0, end: 1.0));

final sceneB2 = sceneA1
    .thenFor(duration: const Duration(milliseconds: 500))
    .tween('x', Tween(begin: 1.0, end: 2.0));

Absolute scenes

You can add scenes anywhere in the timeline of your tween by using tween.scene(). You just need to provide two of these parameters:

• begin (start time of the scene)
• duration (duration of the scene)
• end (end time of the scene)

final tween = MovieTween();

// start at 0ms and end at 1500ms
final scene1 = tween.scene(
  duration: const Duration(milliseconds: 1500),
);

// start at 200ms and end at 900ms
final scene2 = tween.scene(
  begin: const Duration(milliseconds: 200),
  duration: const Duration(milliseconds: 700),
);

// start at 700ms and end at 1400ms
final scene3 = tween.scene(
  begin: const Duration(milliseconds: 700),
  end: const Duration(milliseconds: 1400),
);

// start at 1000ms and end at 1600ms
final scene4 = tween.scene(
  duration: const Duration(milliseconds: 600),
  end: const Duration(milliseconds: 1600),
);

Relative scenes

You can also make scenes depend on each other by using thenFor().

final tween = MovieTween();

final firstScene = tween
    .scene(
      begin: const Duration(seconds: 0),
      duration: const Duration(seconds: 2),
    )
    .tween('x', ConstantTween<int>(0));

// secondScene references the firstScene
final secondScene = firstScene
    .thenFor(
      delay: const Duration(milliseconds: 200),
      duration: const Duration(seconds: 2),
    )
    .tween('x', ConstantTween<int>(1));

It also possible to add an optional delay to add further time between the scenes.

Hint on code style

By using builder style Dart syntax and comments you can easily create a well-readable animation.

MovieTween()

    /// fade in
    .scene(
      begin: const Duration(seconds: 0),
      duration: const Duration(milliseconds: 300),
    )
    .tween('x', Tween<double>(begin: 0.0, end: 100.0))
    .tween('y', Tween<double>(begin: 0.0, end: 200.0))

    /// grow
    .thenFor(duration: const Duration(milliseconds: 700))
    .tween('x', Tween<double>(begin: 100.0, end: 200.0))
    .tween('y', Tween<double>(begin: 200.0, end: 400.0))

    /// fade out
    .thenFor(duration: const Duration(milliseconds: 300))
    .tween('x', Tween<double>(begin: 200.0, end: 0.0))
    .tween('y', Tween<double>(begin: 400.0, end: 0.0));

Animate properties

You can use tween() to specify a tween for single property.

final tween = MovieTween();
final scene = tween.scene(end: const Duration(seconds: 1));

scene.tween('width', Tween(begin: 0.0, end: 100.0));
scene.tween('color', ColorTween(begin: Colors.red, end: Colors.blue));

You can fine tune the timing with shiftBegin or shiftEnd for each property.

scene.tween('width', Tween(begin: 0.0, end: 100.0),
    shiftBegin: const Duration(milliseconds: 200), // start later
    shiftEnd: const Duration(milliseconds: -200) // end earlier
    );

Curves

You can customize the default easing curve at MovieTween, scene or property tween level.

final tween = MovieTween(curve: Curves.easeIn);

// scene1 will use Curves.easeIn defined by the MovieTween
final scene1 = tween.scene(duration: const Duration(seconds: 1));

// scene2 will use Curves.easeOut
final scene2 =
    tween.scene(duration: const Duration(seconds: 1), curve: Curves.easeOut);

// will use Curves.easeIn defined by the MovieTween
scene1.tween('value1', Tween(begin: 0.0, end: 100.0));

// will use Curves.easeOut defined by scene2
scene2.tween('value2', Tween(begin: 0.0, end: 100.0));

// will use Curves.easeInOut defined by property tween
scene2.tween('value3', Tween(begin: 0.0, end: 100.0),
    curve: Curves.easeInOut);

Extrapolation

All values that are not explicitly set in the timeline will be extrapolated.

final tween = MovieTween()

  // implicitly use 100.0 for width values from 0.0s - 1.0s

  // 1.0s - 2.0s
  ..scene(
    begin: const Duration(seconds: 1),
    duration: const Duration(seconds: 1),
  ).tween('width', Tween<double>(begin: 100.0, end: 200.0))

  // implicitly use 200.0 for width values from 2.0s - 3.0s

  // 3.0s - 4.0s
  ..scene(
    begin: const Duration(seconds: 3),
    end: const Duration(seconds: 4),
  ).tween('height', Tween<double>(begin: 400.0, end: 500.0));

Use developer tools

Creating complex tweens with multiple or staggered properties can be time consuming to create and maintain. I recommend using the Animation Developer Tools to streamline this process.

Animation duration

Normally an Animatable or Tween doesn't contain a duration information. But MovieTween class contains a duration property that contains the total duration of the animation.

@override
Widget build(BuildContext context) {
  final tween = MovieTween()
    ..tween('width', Tween<double>(begin: 0.0, end: 100.0),
        duration: const Duration(milliseconds: 700))
    ..tween('height', Tween<double>(begin: 300.0, end: 200.0),
        duration: const Duration(milliseconds: 700));

  return PlayAnimationBuilder<Movie>(
    tween: tween,
    duration: tween.duration, // use duration from MovieTween
    builder: (context, value, _) {
      return Container(
        width: value.get('width'),
        height: value.get('height'),
        color: Colors.yellow,
      );
    },
  );
}

Hint: You can also multiply the duration value with a numeric factor in order to speed up or slow down an animation.

Of cause you can also use an own Duration for the animation.

Animation Mixin

It reduces boilerplate code when using AnimationController instances.

Basic usage pattern

Create an AnimationController just by adding AnimationMixin to your stateful widget:

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

class MyAnimatedWidget extends StatefulWidget {
  const MyAnimatedWidget({Key? key}) : super(key: key);

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

// Add AnimationMixin to state class
class _MyAnimatedWidgetState extends State<MyAnimatedWidget>
    with AnimationMixin {
  late Animation<double> size;

  @override
  void initState() {
    size = Tween<double>(begin: 0.0, end: 200.0).animate(controller);
    controller.play();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container(width: size.value, height: size.value, color: Colors.red);
  }
}

💪 The AnimationMixin generates a preconfigured AnimationController as controller. You can just use it. No need to worry about initialization or disposing.

Create multiple AnimationController

With multiple AnimationController you can have many parallel animations at the same time.

Anicoto's AnimationMixin enhances your state class with a method createController() to create multiple managed* AnimationController. ("Managed" means that you don't need to care about initialization and disposing.)

Create a managed AnimationController

First create a class variable of type AnimationController. Then inside the initState() {...} method call createController(). That's all.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

class MyAnimatedWidget extends StatefulWidget {
  const MyAnimatedWidget({Key? key}) : super(key: key);

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

// use AnimationMixin
class _MyAnimatedWidgetState extends State<MyAnimatedWidget>
    with AnimationMixin {
  late AnimationController sizeController; // declare custom AnimationController
  late Animation<double> size;

  @override
  void initState() {
    sizeController = createController(); // create custom AnimationController
    size = Tween<double>(begin: 0.0, end: 200.0).animate(sizeController);
    sizeController.play(duration: const Duration(seconds: 5));
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container(width: size.value, height: size.value, color: Colors.red);
  }
}

Create many managed AnimationController

Anicoto allows you to have as many AnimationController you want. Behind the scenes it keeps track of them.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

class MyAnimatedWidget extends StatefulWidget {
  const MyAnimatedWidget({Key? key}) : super(key: key);

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

class _MyAnimatedWidgetState extends State<MyAnimatedWidget>
    with AnimationMixin {
  late AnimationController widthController;
  late AnimationController heightController;
  late AnimationController colorController;

  late Animation<double> width;
  late Animation<double> height;
  late Animation<Color?> color;

  @override
  void initState() {
    widthController = createController()
      ..mirror(duration: const Duration(seconds: 5));
    heightController = createController()
      ..mirror(duration: const Duration(seconds: 3));
    colorController = createController()
      ..mirror(duration: const Duration(milliseconds: 1500));

    width = Tween<double>(begin: 100.0, end: 200.0).animate(widthController);
    height = Tween<double>(begin: 100.0, end: 200.0).animate(heightController);
    color = ColorTween(begin: Colors.red, end: Colors.blue)
        .animate(colorController);

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        width: width.value, height: height.value, color: color.value);
  }
}

Shortcuts for AnimationController

The extension for AnimationController adds four convenience functions:

• controller.play() plays animation and stops at the end.

• controller.playReverse() plays animation reversed and stops at the start.

• controller.loop() repetitively plays the animation from start to the end.

• controller.mirror() repetitively plays the animation forward, then backwards, then forward and so on.

Each of these methods take an optional duration named parameter to configure your animation action within one line of code.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

void someFunction(AnimationController controller) {
  controller.play(duration: const Duration(milliseconds: 1500));
  controller.playReverse(duration: const Duration(milliseconds: 1500));
  controller.loop(duration: const Duration(milliseconds: 1500));
  controller.mirror(duration: const Duration(milliseconds: 1500));
}

You can use these methods nicely along the already existing controller.stop() and controller.reset() methods.

Animation Developer Tools

The Animation Developer Tools allow you to create or review your animation step by step.

Basic usage pattern

Wrap your UI with the AnimationDeveloperTools widget.

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

class MyPage extends StatelessWidget {
  const MyPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // put DevTools very high in the widget hierarchy
      body: AnimationDeveloperTools(
        child: Container(), // your UI
      ),
    );
  }
}

Enable developer mode on the animation you want to debug.

Using Animation Builder widgets

The Animation Builder widgets

• PlayAnimationBuilder
• LoopAnimationBuilder
• MirrorAnimationBuilder
• CustomAnimationBuilder

have a constructor parameter developerMode that can be set to true. It will connect to the closest AnimationDeveloperTools widget.

Example

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

void main() => runApp(const MaterialApp(home: Scaffold(body: MyPage())));

class MyPage extends StatelessWidget {
  const MyPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      // put DevTools very high in the widget hierarchy
      child: AnimationDeveloperTools(
        child: Center(
          child: PlayAnimationBuilder<double>(
            tween: Tween<double>(begin: 0.0, end: 100.0),
            duration: const Duration(seconds: 1),
            developerMode: true, // enable developer mode
            builder: (context, value, child) {
              return Container(
                width: value,
                height: value,
                color: Colors.blue,
              );
            },
          ),
        ),
      ),
    );
  }
}

Using Animation Mixin

If your stateful widget uses AnimationMixin to manage your instances of AnimationController you can call enableDeveloperMode() to connect to the clostest AnimationDeveloperMode widget.

Example

import 'package:flutter/material.dart';
import 'package:simple_animations/simple_animations.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(
        body: SafeArea(
          // put DevTools very high in the widget hierarchy
          child: AnimationDeveloperTools(
            child: Center(
              child: MyAnimation(),
            ),
          ),
        ),
      ),
    );
  }
}

class MyAnimation extends StatefulWidget {
  const MyAnimation({Key? key}) : super(key: key);

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

class _MyAnimationState extends State<MyAnimation> with AnimationMixin {
  late Animation<double> size;

  @override
  void initState() {
    size = Tween<double>(begin: 0.0, end: 100.0).animate(controller);
    enableDeveloperMode(controller); // enable developer mode
    controller.forward();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container(width: size.value, height: size.value, color: Colors.blue);
  }
}

Features and tricks

The Animation Developer Tools come with several features that simplify your developer life:

• Regardless of the real animation, with developer mode activated the animation will always loop.
• You can use Flutter hot reloading for editing and debugging if your tween is created stateless.
• Use the slider to edit the animated scene while pausing.
• You can slow down the animation to look out for certain details.
• Use the interval buttons to focus on a time span of the animation.