Visual changes happen as a series of operations, rather than all at once.
Complete staggered animation
Like all interactive widgets, the complete animation consists of a widget pair: a stateless and a stateful widget.
The stateless widget specifies the Tweens, defines the Animation objects, and provides a build() function responsible for building the animating portion of the widget tree.
The stateful widget creates the controller, plays the animation, and builds the non-animating portion of the widget tree. The animation begins when a tap is detected anywhere in the screen.
Semantic portal