void forEachTween(TweenVisitor visitor)

Subclasses must implement this function by running through the following steps for each animatable facet in the class:

  1. Call the visitor callback with three arguments, the first argumentbeing the current value of the Tween object that represents thetween (initially null), the second argument, of type T, being the valueon the Widget (config) that represents the current target value of thetween, and the third being a callback that takes a value T (which willbe the second argument to the visitor callback), and that returns anTween object for the tween, configured with the given valueas the begin value.

  2. Take the value returned from the callback, and store it. This is thevalue to use as the current value the next time that the forEachTween()method is called.

Source 

void forEachTween(TweenVisitor<dynamic> visitor);