All 7 Flutter Animations Basics questions
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What is an AnimationController in Flutter, and how does it act as the central driver that actually controls the progress and timing of an animation? What is the difference between implicit and explicit animations in Flutter, and which specific approach is generally simpler to actually implement for a straightforward, everyday animation need? How does a Tween work together with an AnimationController to actually define the specific range of values, such as a color or a position, that an animation should smoothly transition between? What are animation curves in Flutter, such as Curves.easeIn or Curves.bounceOut, and how do they let you control the specific pacing and feel of an animation rather than it always simply moving at a perfectly constant, linear speed? How can you properly coordinate several separate, related animations together, such as a fade combined with a scale effect, ensuring they all play in perfect sync using a single shared underlying AnimationController? What performance considerations become important when building a screen containing several simultaneous, continuously running animations, and how can Flutter DevTools help identify a genuine animation related performance problem?
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How does the AnimatedBuilder widget let you efficiently rebuild only the specific part of your widget tree that actually needs to change on every single animation frame, rather than rebuilding an entire larger, unrelated widget subtree unnecessarily?

Intermediate

Answer

The AnimatedBuilder widget listens to a provided Animation object and automatically calls its own builder function on every single frame update while that animation is actively running, and by passing an already constructed, unchanging child widget into AnimatedBuilder through its dedicated child parameter, Flutter can efficiently avoid rebuilding that potentially expensive child widget on every single frame, since only the specific, smaller builder function itself actually needs to run repeatedly, which is a particularly important optimization for animations involving a genuinely expensive child widget that should not need to be needlessly reconstructed many times every single second.
AnimatedBuilder(
  animation: controller,
  builder: (context, child) {
    return Transform.rotate(angle: controller.value * 6.28, child: child);
  },
  child: ExpensiveWidget(),
)
Real-world example A custom loading spinner uses AnimatedBuilder to continuously rotate a fairly complex child icon widget, passing that expensive child through the dedicated child parameter to avoid it being needlessly rebuilt from scratch on every single animation frame.

Common follow-ups: What is the difference between using AnimatedBuilder and simply calling setState directly inside an animation listener?;How does this specific optimization pattern relate to how the child parameter works on other custom widgets?

Flutter Performance Optimization;Custom Widgets & Reusable Components
All 7 Flutter Animations Basics questions