custom-plugin-flutter: Animations Skill

Quick Start - Production Animation Pattern

class AnimatedProductCard extends StatefulWidget {
  final Product product;
  final bool isSelected;

  const AnimatedProductCard({
    required this.product,
    required this.isSelected,
  });

  @override
  State<AnimatedProductCard> createState() => _AnimatedProductCardState();
}

class _AnimatedProductCardState extends State<AnimatedProductCard>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<double> _scaleAnimation;
  late final Animation<double> _opacityAnimation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(milliseconds: 200),
      vsync: this,
    );

    _scaleAnimation = Tween<double>(begin: 1.0, end: 0.95).animate(
      CurvedAnimation(parent: _controller, curve: Curves.easeInOut),
    );

    _opacityAnimation = Tween<double>(begin: 1.0, end: 0.8).animate(
      CurvedAnimation(parent: _controller, curve: Curves.easeInOut),
    );
  }

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

  void _onTapDown(TapDownDetails details) => _controller.forward();
  void _onTapUp(TapUpDetails details) => _controller.reverse();
  void _onTapCancel() => _controller.reverse();

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTapDown: _onTapDown,
      onTapUp: _onTapUp,
      onTapCancel: _onTapCancel,
      child: AnimatedBuilder(
        animation: _controller,
        builder: (context, child) {
          return Transform.scale(
            scale: _scaleAnimation.value,
            child: Opacity(
              opacity: _opacityAnimation.value,
              child: child,
            ),
          );
        },
        child: AnimatedContainer(
          duration: const Duration(milliseconds: 300),
          decoration: BoxDecoration(
            border: Border.all(
              color: widget.isSelected ? Colors.blue : Colors.grey,
              width: widget.isSelected ? 2 : 1,
            ),
            borderRadius: BorderRadius.circular(12),
          ),
          child: ProductContent(product: widget.product),
        ),
      ),
    );
  }
}

1. Implicit Animations

Built-in Animated Widgets

// AnimatedContainer - Animate multiple properties
AnimatedContainer(
  duration: Duration(milliseconds: 300),
  curve: Curves.easeInOut,
  width: isExpanded ? 300 : 100,
  height: isExpanded ? 200 : 100,
  decoration: BoxDecoration(
    color: isActive ? Colors.blue : Colors.grey,
    borderRadius: BorderRadius.circular(isExpanded ? 16 : 8),
    boxShadow: isActive ? [BoxShadow(blurRadius: 10)] : [],
  ),
  child: content,
)

// AnimatedOpacity
AnimatedOpacity(
  opacity: isVisible ? 1.0 : 0.0,
  duration: Duration(milliseconds: 200),
  child: content,
)

// AnimatedPositioned (inside Stack)
AnimatedPositioned(
  duration: Duration(milliseconds: 300),
  left: isLeft ? 0 : 100,
  top: isTop ? 0 : 100,
  child: widget,
)

// AnimatedSwitcher - Cross-fade between widgets
AnimatedSwitcher(
  duration: Duration(milliseconds: 300),
  transitionBuilder: (child, animation) {
    return FadeTransition(opacity: animation, child: child);
  },
  child: Text(
    currentText,
    key: ValueKey(currentText), // Important!
  ),
)

// TweenAnimationBuilder - Custom implicit animation
TweenAnimationBuilder<double>(
  tween: Tween(begin: 0, end: progress),
  duration: Duration(milliseconds: 500),
  builder: (context, value, child) {
    return CircularProgressIndicator(value: value);
  },
)

2. Explicit Animations

AnimationController Pattern

class ExplicitAnimationWidget extends StatefulWidget {
  @override
  State<ExplicitAnimationWidget> createState() => _ExplicitAnimationWidgetState();
}

class _ExplicitAnimationWidgetState extends State<ExplicitAnimationWidget>
    with TickerProviderStateMixin {
  late final AnimationController _controller;
  late final Animation<Offset> _slideAnimation;
  late final Animation<double> _fadeAnimation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: Duration(milliseconds: 500),
      vsync: this,
    );

    _slideAnimation = Tween<Offset>(
      begin: Offset(0, 1),
      end: Offset.zero,
    ).animate(CurvedAnimation(
      parent: _controller,
      curve: Interval(0.0, 0.6, curve: Curves.easeOut),
    ));

    _fadeAnimation = Tween<double>(
      begin: 0,
      end: 1,
    ).animate(CurvedAnimation(
      parent: _controller,
      curve: Interval(0.3, 1.0, curve: Curves.easeIn),
    ));

    _controller.forward();
  }

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

  @override
  Widget build(BuildContext context) {
    return SlideTransition(
      position: _slideAnimation,
      child: FadeTransition(
        opacity: _fadeAnimation,
        child: Content(),
      ),
    );
  }
}

Animation Transitions

// Built-in transitions
FadeTransition(opacity: animation, child: widget)
SlideTransition(position: offsetAnimation, child: widget)
ScaleTransition(scale: animation, child: widget)
RotationTransition(turns: animation, child: widget)
SizeTransition(sizeFactor: animation, child: widget)

// AnimatedBuilder - Custom rendering
AnimatedBuilder(
  animation: _controller,
  builder: (context, child) {
    return Transform(
      transform: Matrix4.identity()
        ..setEntry(3, 2, 0.001)
        ..rotateY(_controller.value * pi),
      alignment: Alignment.center,
      child: child,
    );
  },
  child: Card(),
)

3. Hero Animations

// Source screen
Hero(
  tag: 'product-${product.id}',
  child: Image.network(product.imageUrl),
)

// Destination screen
Hero(
  tag: 'product-${product.id}',
  child: Image.network(product.imageUrl),
)

// Custom Hero flight
Hero(
  tag: 'avatar',
  flightShuttleBuilder: (
    flightContext,
    animation,
    flightDirection,
    fromHeroContext,
    toHeroContext,
  ) {
    return AnimatedBuilder(
      animation: animation,
      builder: (context, _) {
        return CircleAvatar(
          radius: lerpDouble(40, 60, animation.value),
        );
      },
    );
  },
  child: CircleAvatar(),
)

4. Staggered Animations

class StaggeredList extends StatefulWidget {
  @override
  State<StaggeredList> createState() => _StaggeredListState();
}

class _StaggeredListState extends State<StaggeredList>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  final List<Animation<Offset>> _animations = [];

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: Duration(milliseconds: 1000),
      vsync: this,
    );

    // Create staggered animations
    for (int i = 0; i < 5; i++) {
      final start = i * 0.1;
      final end = start + 0.4;
      _animations.add(
        Tween<Offset>(begin: Offset(1, 0), end: Offset.zero).animate(
          CurvedAnimation(
            parent: _controller,
            curve: Interval(start, end, curve: Curves.easeOut),
          ),
        ),
      );
    }

    _controller.forward();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: List.generate(5, (index) {
        return SlideTransition(
          position: _animations[index],
          child: ListTile(title: Text('Item $index')),
        );
      }),
    );
  }
}

5. Physics-Based Animations

// Spring simulation
class SpringAnimation extends StatefulWidget {
  @override
  State<SpringAnimation> createState() => _SpringAnimationState();
}

class _SpringAnimationState extends State<SpringAnimation>
    with SingleTickerProviderStateMixin {
  late final AnimationController _controller;
  late Animation<double> _animation;

  final SpringDescription spring = SpringDescription(
    mass: 1,
    stiffness: 100,
    damping: 10,
  );

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(vsync: this);

    final simulation = SpringSimulation(spring, 0, 1, 0);
    _controller.animateWith(simulation);

    _animation = _controller.drive(Tween(begin: 0.0, end: 100.0));
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _animation,
      builder: (context, child) {
        return Transform.translate(
          offset: Offset(0, _animation.value),
          child: child,
        );
      },
      child: Ball(),
    );
  }
}

6. Lottie & Rive Integration

// Lottie animation
import 'package:lottie/lottie.dart';

Lottie.asset(
  'assets/loading.json',
  width: 200,
  height: 200,
  fit: BoxFit.contain,
  repeat: true,
  animate: true,
  onLoaded: (composition) {
    _controller.duration = composition.duration;
  },
)

// Rive animation
import 'package:rive/rive.dart';

RiveAnimation.asset(
  'assets/animation.riv',
  fit: BoxFit.cover,
  stateMachines: ['StateMachine1'],
  onInit: (artboard) {
    final controller = StateMachineController.fromArtboard(
      artboard,
      'StateMachine1',
    );
    artboard.addController(controller!);
    _trigger = controller.findInput<bool>('trigger') as SMITrigger;
  },
)

7. Page Transitions

// Custom page route
class FadePageRoute<T> extends PageRouteBuilder<T> {
  final Widget page;

  FadePageRoute({required this.page})
      : super(
          pageBuilder: (context, animation, secondaryAnimation) => page,
          transitionsBuilder: (context, animation, secondaryAnimation, child) {
            return FadeTransition(opacity: animation, child: child);
          },
          transitionDuration: Duration(milliseconds: 300),
        );
}

// Slide + fade combined
transitionsBuilder: (context, animation, secondaryAnimation, child) {
  final offsetAnimation = Tween<Offset>(
    begin: Offset(1.0, 0.0),
    end: Offset.zero,
  ).animate(CurvedAnimation(
    parent: animation,
    curve: Curves.easeInOut,
  ));

  return SlideTransition(
    position: offsetAnimation,
    child: FadeTransition(
      opacity: animation,
      child: child,
    ),
  );
}

8. Performance Optimization

// Use const where possible
const AnimatedContainer(...)

// RepaintBoundary for expensive animations
RepaintBoundary(
  child: AnimatedWidget(),
)

// AnimatedBuilder isolates rebuilds
AnimatedBuilder(
  animation: _controller,
  child: ExpensiveWidget(), // Not rebuilt
  builder: (context, child) {
    return Transform.scale(
      scale: _controller.value,
      child: child, // Reused
    );
  },
)

// Avoid layout-triggering animations
// Good: Transform, Opacity
// Avoid: width/height in tight loops

Troubleshooting Guide

Issue: Animation jank (dropped frames)

1. Use RepaintBoundary to isolate
2. Profile with DevTools Performance
3. Avoid layout changes during animation
4. Use AnimatedBuilder, not setState
5. Check for heavy build methods

Issue: Animation doesn't start

1. Verify AnimationController.forward() called
2. Check vsync: this (TickerProviderStateMixin)
3. Verify widget is mounted before animating
4. Check duration is set

Issue: Animation leaks memory

1. Dispose AnimationController in dispose()
2. Cancel any listeners
3. Use mounted check before setState

Animation Selection Guide

Need	Solution
Simple property change	AnimatedContainer
Cross-fade widgets	AnimatedSwitcher
Custom timing control	AnimationController
Shared element	Hero
List items appearing	Staggered animations
Natural motion	Physics simulation
Complex vector	Lottie/Rive

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Create fluid, 60fps animations in Flutter.