Flutter Animations FAQs

• How do animations fit into the reactive/stateful model?
• Are they a bridge between states?
• Do they exist outside of state? because the things they are tied to usually have state.
• Why do you need an AnimationController and an Animation object if AnimationController is subclassed from Animation?

This page includes frequently asked questions about Flutter animations.
Let us know what questions you have about animations!

How do animations fit into the reactive/stateful model?

Animations are driven by a change in the state of an AnimationController (a ticker really). An animated widget’s visuals “react to” this changing state and all of the animation’s that are chained to it.

Are they a bridge between states?

Sometimes that’s a simple way to explain what’s going on yes. For example if an AnimatedContainer is rebuilt with a new backgroundColor, it automatically (implicitly) animates from the old backgroundColor to the new one. That’s an animated state change.

Do they exist outside of state? because the things they are tied to usually have state.

Not really. Only stateful widgets can respond to animations with setState(), to rebuild or react.

Why do you need an AnimationController and an Animation object if AnimationController is subclassed from Animation?

You don’t need both. The AnimationController is usually used to drive other Animations (chaining). You could build animated widgets that just listened to an AnimationController and computed tween values based on the AnimationController’s value. All of the Tween, Curve, and Animation classes exist to make doing that simpler and easier.