How to Implement Custom Animation Curves in Flutter

1. Understanding Core Components

Flutter handles animations using several core concepts:

• AnimationController: Controls the timing and state of animations.
• Tween: Defines the start and end values of the animation.
• Curve: Defines the speed variation of the animation.

2. Using Built-in Curves

Flutter provides many built-in curves (Curves), such as Curves.linear, Curves.easeIn, etc., which can be directly applied to simple animation effects.

3. Creating Custom Curves

If built-in curves do not meet your needs, you can create your own animation curves by inheriting from the Curve class.

dart
import 'package:flutter/animation.dart';

class MyCustomCurve extends Curve {
  @override
  double transform(double t) {
    // Example: A simple custom cubic curve
    return t * t * t;
  }
}

4. Applying Custom Curves

After creating a custom curve, you can use it in animations.

dart
AnimationController controller = AnimationController(
  duration: const Duration(seconds: 2),
  vsync: this, // This requires a TickerProvider type parameter
);

Animation<double> animation = Tween(begin: 0.0, end: 1.0).animate(
  CurvedAnimation(
    parent: controller,
    curve: MyCustomCurve(),
  ),
);

// Using addListener and setState to update the UI
animation.addListener(() {
  setState(() {
    // UI update
  });
});

controller.forward();

5. Example: Implementing Animation with Custom Curves

Here is a complete example demonstrating how to use custom animation curves in a Flutter application.

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {
  AnimationController _controller;
  Animation<double> _animation;

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

    _animation = Tween(begin: 0.0, end: 300.0).animate(
      CurvedAnimation(
        parent: _controller,
        curve: MyCustomCurve(), // Using the custom curve
      ),
    )..addListener(() {
        setState(() {});
      });

    _controller.forward();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Container(
          height: _animation.value,
          width: _animation.value,
          color: Colors.blue,
        ),
      ),
    );
  }

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

class MyCustomCurve extends Curve {
  @override
  double transform(double t) {
    return t * t * t;
  }
}

In this example, we create a simple animation where the size changes from 0 to 300, using our custom cubic curve effect.

6. Summary

By following the above steps, you can implement custom animation curves in Flutter to meet specific user experience requirements. Custom animation curves can make your application's animations more personalized and engaging.