activate method
Called when this WidgetModel and Elementary are reinserted into
the tree after having been removed via deactivate.
In most cases, after a WidgetModel has been deactivated, it is not reinserted into the tree, and its dispose method will be called to signal that it is ready to be garbage collected.
In some cases, however, after a WidgetModel has been deactivated,
it will reinserted it into another part of the tree (e.g., if there is a
subtree uses a GlobalKey that match with key of the Elementary
linked with this WidgetModel).
This method does not called the first time a WidgetModel object is inserted into the tree. Instead, calls initWidgetModel in that situation.
Implementations of this method should start with a call to the inherited
method, as in super.activate().
Implementation
@protected
@mustCallSuper
@visibleForTesting
void activate() {}