13.7. Flutter Animations: Custom Animations

Animations in Flutter are an essential part of creating an attractive and dynamic app. Through animations, you can add movement and life to your application components, making the user experience more immersive and interactive. In this topic, we'll explore how to create custom animations in Flutter using the powerful Dart framework.

Understanding Animations in Flutter

In Flutter, an animation is essentially a sequence of values ​​that change over time. For example, if you wanted to move a widget from one side of the screen to the other, the animation would be a sequence of positions that the widget must occupy at different times.

Flutter provides a rich animation library that lets you create a wide variety of animations, from simple linear movements to complex animation sequences.

Creating Custom Animations

To create a custom animation in Flutter, you need to follow some basic steps:

1. Create an Animation object: This object represents the sequence of values ​​that the animation will produce.
2. Create an AnimationController object: This object controls the progression of the animation.
3. Associate the animation with the widget you want to animate.
4. Start animation.

It's important to note that in Flutter, animations are "pulled", not "pushed". This means that it is the widget being animated that requests the animation values, not the animation that "pushes" the values ​​to the widget.

Custom Animation Example

Here is an example of how you can create a custom animation in Flutter:

```dart
class MyAnimatedWidget extends StatefulWidget {
  @override
  _MyAnimatedWidgetState createState() => _MyAnimatedWidgetState();
}

class _MyAnimatedWidgetState extends State with SingleTickerProviderStateMixin {
  Animation animation;
  AnimationController controller;

  @override
  void initState() {
    super.initState();

    controller = AnimationController(
      duration: const Duration(seconds: 2),
      vsync: this,
    );

    animation = Tween(begin: 0, end: 200).animate(controller)
      ..addListener(() {
        setState(() {
          // the state that has changed here is the animation object’s value
        });
      });

    controller.forward();
  }

  @override
  Widget build(BuildContext context) => Container(
    margin: EdgeInsets.symmetric(vertical: 10.0),
    height: animation.value,
    width: animation.value,
    child: FlutterLogo(),
  );

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

This is a simple example, but the possibilities are endless. You can combine multiple animations, create complex animations with custom curves, animate multiple widgets at the same time, and much more.

Conclusion

Animations are a key part of creating beautiful and dynamic apps in Flutter. With Flutter's library of animations and a little creativity, you can bring your widgets to life in surprising and engaging ways.

This article is just the beginning. Flutter offers many more features for creating animations, including physical animations, scrolling animations, page transitions, hero animations and much more. With time and practice, you can become a master of Flutter animations.