fleet 0.5.0+1

An animation Framework for Flutter. It is state-based, declarative, extensible, composable and easy to use.

⚠️ This package is in an early state of development. If you find any bugs or have any suggestions, please open an issue.

Fleet is an animation framework for Flutter.

• State-based: Animate transitions from one state to another.
• Declarative: Describe an animation and apply it to a state change. No need to manage AnimationControllers or Tweens.
• Animatable widgets: Comes out of the box with general purpose widgets that support animating with Fleet.
  • Extensible: Any widget can be made to support animating with Fleet.
  • Flexible: Animatable widgets can be used with or without animations.
  • Composable: Widgets that build on animatable widgets are automatically animatable.
  • Animate parameters individually: Animate parameters of animatable widget individually, e.g. with different curves.
• User-friendly: Add and change animations with little refactoring.

Getting started

Add Fleet to your pubspec.yaml:

flutter pub add fleet

Now you're ready to use Fleet in your Flutter app.

Take a look a the examples or continue to the introduction to Fleet.

Introduction

Fleet has been heavily inspired by the animation framework that comes with SwiftUI. If you are familiar with it, you will find most concepts familiar.

I'm going to walk you through adding a simple animation to a widget. Below is the unanimated version of the widget:

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

class MyWidget extends StatefulWidget {
  const MyWidget({super.key});

  @override
  State<MyWidget> createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  var _active = false;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        setState(() {
          _active = !_active;
        });
      },
      child: ColoredBox(
        color: _active ? Colors.blue : Colors.grey,
      ),
    );
  }
}

Now lets animate the state change of _active:

-class _MyWidgetState extends State<MyWidget> {
+class _MyWidgetState extends State<MyWidget> with AnimatingStateMixin {
   var _active = false;

   @override
   Widget build(BuildContext context) {
     return GestureDetector(
       onTap: () {
-        setState(() {
+        setStateWithAnimation(Curves.ease.animation(250.ms), () {
           _active = !_active;
         });
       },
-      child: ColoredBox(
+      child: FleetColoredBox(
         color: _active ? Colors.blue : Colors.grey,
       ),
     );
   }
 }

We made the following changes:

1. Mixin AnimatingStateMixin to _MyWidgetState, so we can use setStateWithAnimation.
2. Use setStateWithAnimation to specify the animation that we want to apply to the state change.
3. Use FleetColoredBox instead of ColoredBox.

The FleetColoredBox widget is a drop-in replacement for ColoredBox that supports animating with Fleet. Widgets that support animating with Fleet don't have any special parameters related to animation and can be used without animation, just as well.

Fleet provides drop-in replacements for a number of generally useful Flutter framework widgets (all with the prefix A). Any widget can be made to support state-based animation through components provided by Fleet (see AnimatableStatelessWidget). Issues or PRs for adding support for more widgets are welcome!

Note that we did not explicitly tell setStateWithAnimation what to animate. This is because Fleet uses a state-based approach. All state changes caused by executing the provided callback will be animated. Even the state changes which are indirect, like the color parameter of FleetColoredBox going from Colors.grey to Colors.blue. Fleet does this by tracking the state of animatable parameters of animatable widgets from one build to the next.

Curves.ease.animation(250.ms) creates an AnimationSpec that we pass to setStateWithAnimation to specify how to animate from the old to the new state.

.animate is an extension method on Curve that creates an AnimationSpec form the curve. It optionally takes a Duration. For a nicer syntax for specifying Durations, Fleet provides extensions on int, e.g 250.ms is equivalent to Duration(milliseconds: 250).

Animatable widgets

The following drop-in replacements for Flutter framework widgets are provided for animating with Fleet:

• FleetAlign
• FleetAspectRatio
• FleetCenter
• FleetColoredBox
• FleetColumn
• FleetConstrainedBox
• FleetContainer
• FleetDecoratedBox
• FleetFittedBox
• FleetFlex
• FractionalTranslation
• FleetFractionallySizedBox
• FleetLimitedBox
• FleetOpacity
• FleetOverflowBox
• FleetPadding
• FleetPositioned
• FleetPositionedDirectional
• FleetRow
• FleetSizedBox
• FleetSizedOverflowBox
• FleetSliverOpacity
• FleetSliverPadding
• FleetTransform

See the fleet_imports package for an way to start using these widgets with minimal changes to your code.

The following provided widgets are specific to Fleet:

• UniformPadding

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Gabriel Terwesten • GitHub @blaugold • Twitter @GTerwesten • Medium @gabriel.terwesten