activate method
void
activate()
Called when this object is reinserted into the tree after having been removed via deactivate.
Implementation
void activate() {
/// In some cases, however, after a [State] object has been deactivated, the
/// framework will reinsert it into another part of the tree (e.g., if the
/// subtree containing this [State] object is grafted from one location in
/// the tree to another due to the use of a [GlobalKey]). If that happens,
/// the framework will call [activate] to give the [State] object a chance to
/// reacquire any resources that it released in [deactivate]. It will then
/// also call [build] to give the object a chance to adapt to its new
/// location in the tree.
///
/// The framework does not call this method the first time a [State] object
/// is inserted into the tree. Instead, the framework calls [initState] in
/// that situation.
}