1. Introduction

Welcome to this tutorial on creating custom animations in Flutter. The aim of this tutorial is to guide you on how to create and implement your own unique animations in your Flutter applications.

By the end of this tutorial, you will learn:

• The basics of Flutter animations
• How to create custom animations
• How to implement these animations in your application

Prerequisites:
- Basic knowledge of Dart programming language
- Basic understanding of Flutter development
- A working Flutter development environment

2. Step-by-Step Guide

Animations in Flutter are encapsulated as Animation objects. These objects can be either of two types: Tweens and Physics-based animations. The Animation object knows the current state of an animation (for example, it’s completed or it’s stopped at a certain value), but it doesn’t know anything about what’s on the screen.

Let's dive into coding to understand it better.

3. Code Examples

Example 1: Simple Animation

This example will show a logo that fades out over a three-second duration.

class LogoApp extends StatefulWidget {
  _LogoAppState createState() => _LogoAppState();
}

class _LogoAppState extends State<LogoApp> with SingleTickerProviderStateMixin {
  Animation<double> animation;
  AnimationController controller;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(duration: const Duration(seconds: 3), vsync: this);
    animation = Tween<double>(begin: 1, end: 0).animate(controller)
      ..addListener(() {
        setState(() {
          // The state that has changed here is the animation object’s value.
        });
      });
    controller.forward();
  }

  @override
  Widget build(BuildContext context) => Opacity(opacity: animation.value, child: FlutterLogo(size: 200));

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }
}

In this code snippet:

• We create an AnimationController that runs an Animation from 1 (fully visible) to 0 (invisible) over three seconds.
• We use addListener to rebuild the widget tree when the animation changes state, updating the opacity of the logo.
• The dispose method is overridden to release resources when they are not needed.

4. Summary

In this tutorial, we have learned:

• The basics of animations in Flutter
• How to create a simple custom animation
• How to implement the animation in a Flutter application

For further learning, you can explore more complex animations and how to combine multiple animations.

5. Practice Exercises

Exercise 1 - Create a Flutter application that displays a square that changes color over five seconds.

Exercise 2 - Extend the application from Exercise 1 to make the square move across the screen while it changes color.

Solutions

Solution 1
You can use the Tween animation with Color as the generic to animate color changes.

Solution 2
To move the square across the screen, you need to animate the position of the square. You can use Positioned widget for this purpose inside a Stack. Then animate the top and left properties of the Positioned widget.

These exercises are designed to give you more practice with animations in Flutter and encourage you to experiment with different animation types and properties.