didChangeDependencies method
This method is also called immediately after initState. Otherwise called only if this State object's Widget is a dependency of InheritedWidget. When a InheritedWidget's build() function is called the dependent widget's build() function is also called but not before their didChangeDependencies() function. Subclasses rarely use this method.
Implementation
@override
@mustCallSuper
void didChangeDependencies() {
super.didChangeDependencies();
// Subscribe this to be informed about changes to route.
_appState?.subscribe(this);
}