child property Null safety
final
The current child widget to display. If there was a previous child, then that child will be faded out using the switchOutCurve, while the new child is faded in with the switchInCurve, over the duration.
If there was no previous child, then this child will fade in using the switchInCurve over the duration.
The child is considered to be "new" if it has a different type or Key (see Widget.canUpdate).
To change the kind of transition used, see transitionBuilder.
Implementation
final Widget? child;