1. Introduction

1.1 Goal of the tutorial

This tutorial aims to introduce the Animation Controller in Flutter. We will learn how to use this powerful tool to create and manage animations in our Flutter applications.

1.2 Learning outcomes

By the end of this tutorial, you will be able to:

• Understand the role of the Animation Controller in Flutter
• Create and manage animations using the Animation Controller
• Implement custom animations in your Flutter applications

1.3 Prerequisites

Before starting this tutorial, you should have:

• A basic understanding of Flutter
• Flutter SDK installed on your system
• An IDE such as Visual Studio Code or Android Studio

2. Step-by-Step Guide

2.1 Understanding the Animation Controller

In Flutter, the Animation Controller is a type of Animation that can stop, reverse, and restart animations. It requires a Duration to determine how long the animation should last.

2.2 Creating an Animation Controller

First, you need to create an instance of the AnimationController. This is usually done in the initState() method of your StatefulWidget.

AnimationController controller;

@override
void initState() {
  super.initState();
  controller = AnimationController(
    duration: const Duration(seconds: 2),
    vsync: this,
  );
}

In the above code, vsync stands for "visual sync". It is an optional property that prevents off-screen animations from consuming unnecessary resources.

3. Code Examples

3.1 Basic Animation

AnimationController controller;
Animation<double> animation;

@override
void initState() {
  super.initState();
  controller = AnimationController(
    duration: const Duration(seconds: 2),
    vsync: this,
  );

  animation = Tween<double>(begin: 0, end: 300).animate(controller)
    ..addListener(() {
      setState(() {
        // This causes the widget to rebuild every time the animation changes value.
      });
    });

  controller.forward();
}

In this example, we use the Tween class to define a range for the animation. The animate() method returns an Animation object, which we then add a listener to. This listener calls setState() every time the animation value changes, causing the widget to rebuild.

3.2 Reverse Animation

controller.reverse();

The reverse() method will play the animation in reverse from its current position.

4. Summary

In this tutorial, we've learned about the Animation Controller in Flutter and how to use it to create custom animations. We've explored how to initiate, reverse, and manage animations, and we've seen how changes in the animation trigger widget rebuilding.

5. Practice Exercises

5.1 Exercise 1

Create a simple animation where an object moves from the left side of the screen to the right.

5.2 Exercise 2

Enhance the previous exercise by making the object move back to the left side of the screen once it reaches the right.

Solutions

5.1 Solution to Exercise 1

AnimationController controller;
Animation<double> animation;

@override
void initState() {
  super.initState();
  controller = AnimationController(
    duration: const Duration(seconds: 2),
    vsync: this,
  );

  animation = Tween<double>(begin: 0, end: 300).animate(controller)
    ..addListener(() {
      setState(() {
      });
    });

  controller.forward();
}

5.2 Solution to Exercise 2

AnimationController controller;
Animation<double> animation;

@override
void initState() {
  super.initState();
  controller = AnimationController(
    duration: const Duration(seconds: 2),
    vsync: this,
  );

  animation = Tween<double>(begin: 0, end: 300).animate(controller)
    ..addListener(() {
      setState(() {
      });
    });

  controller.forward().then((_) {
    controller.reverse();
  });
}

In the second exercise, we use the then() method to wait for the forward animation to finish before starting the reverse animation.