transitionBuilder property
A function that wraps a new child with a primary and secondary animation set define how the child appears and disappears.
This is only called when a new child 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 child and all old children using the new transitionBuilder. The function must not return null.
The child provided to the transitionBuilder may be null.
Implementation
final PageTransitionSwitcherTransitionBuilder transitionBuilder;