transitionBuilder property
A function that wraps a new content with an animation that transitions the content in when the animation runs in the forward direction and out when the animation runs in the reverse direction. This is only called when a new content is set (not for each build), or when a new transitionBuilder is set. If a new transitionBuilder is set, then the transition is rebuilt for the current content and all previous children using the new transitionBuilder. The function must not return null.
Implementation
final ExpansionTransitionBuilder? transitionBuilder;