Introduction

Animated interactions are a hallmark of polished mobile development. In Flutter, the low-level building block for custom animation-driven widgets is AnimatedBuilder (commonly referenced as AnimationBuilder). This tutorial shows how to use AnimatedBuilder effectively to create delightful, efficient UI effects: separating animation logic from build logic, composing multiple transforms, and keeping performance predictable.

Why Use AnimatedBuilder

AnimatedBuilder lets you listen to an Animation and rebuild only the widget subtree that depends on it. Unlike implicit animations (AnimatedContainer, AnimatedOpacity), AnimatedBuilder works with AnimationController and Tween to provide precise timing, curves, and synchronization between multiple animated properties. For flutter mobile development, that means smooth transitions without rebuilding unrelated widgets, reduced layout churn, and full control over easing and repeat behavior.

Key benefits:

• Fine-grained control: drive several properties from a single controller or multiple controllers.

• Separation of concerns: keep animation state in controllers and build logic in the builder callback.

• Performance: avoids setState for every tick; AnimatedBuilder calls the builder directly when the animation ticks.

Core Patterns

Pattern 1 — Single Controller, Multiple Tweens: Create one AnimationController and derive several Animations via Tween.animate to drive opacity, scale, and translation in sync.

Pattern 2 — Composition With Transform: Use Transform, Opacity, or Align inside the builder to apply visual effects without changing layout bounds unnecessarily.

Pattern 3 — Extract Reusable Animated Widgets: Pack an AnimatedBuilder and its controller into a small stateful widget when you need the same effect in multiple places. This keeps your page code tidy and testable.

Example skeleton (controller + AnimatedBuilder):

// In a StatefulWidget
late final AnimationController controller = AnimationController(
  vsync: this, duration: Duration(milliseconds: 600));
final Animation<double> scale = Tween(begin: 0.8, end: 1.0).animate(
  CurvedAnimation(parent: controller, curve: Curves.easeOutBack));

Widget build(BuildContext context) => AnimatedBuilder(
  animation: controller,
  builder: (context, child) => Transform.scale(
    scale: scale.value,
    child: child,
  ),
  child: YourContentWidget(),
);

Examples: Simple Bounce And Combined Effects

Example 1 — Bounce-in Card: Drive scale and shadow elevation from the same controller. Scale uses an elastic curve while elevation ramps linearly to avoid an overshoot in shadow.

Example 2 — Cross-Fade With Translate: Animate both opacity and slide offset: opacity uses a linear curve, offset uses Curves.easeOut. Wrap the target child in a Transform.translate and Opacity inside the builder.

Combined example for a compact animated item:

AnimatedBuilder(
  animation: controller,
  builder: (ctx, child) {
    final t = Curves.easeOut.transform(controller.value);
    return Opacity(
      opacity: t,
      child: Transform.translate(
        offset: Offset(0, (1 - t) * 20),
        child: child,
      ),
    );
  },
  child: ListTile(title: Text('Animated Item')),
)

This pattern keeps the child subtree constant (so it won't rebuild every tick) while the builder applies paint-only transforms.

Performance And Composition

Keep these rules in mind for production mobile development:

• Limit rebuilt subtrees: pass expensive widgets as the child parameter to AnimatedBuilder so they are not rebuilt every frame.

• Use transforms for visual adjustments: Transform and Opacity are cheaper than changing layout constraints.

• Reuse AnimationControllers where possible: creating controllers per frame or per list item can be expensive—dispose controllers in dispose().

• Prefer vsync from a TickerProviderStateMixin to avoid unnecessary CPU/GPU usage.

When composing multiple animations, consider using Interval objects on CurvedAnimation to choreograph sequences from a single controller. That reduces the number of controllers and simplifies synchronization.

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Conclusion

AnimatedBuilder is a foundational tool in Flutter for crafting precise, performant animated UI effects in mobile development. Use it to separate animation timing from widget construction, compose multiple visual effects, and keep heavy widgets out of the per-frame rebuild path by leveraging the builder's child parameter. With controlled controllers, thoughtful curves, and Transform-based painting, you can deliver delightful interactions that feel native and fluid on mobile devices.