dispose method
Marks the BuildContext as disposed.
Creators of this object must call dispose when their Element is unmounted, i.e. when State.dispose is called.
Implementation
void dispose() {
// TODO(polina-c): stop duplicating code across disposables
// https://github.com/flutter/flutter/issues/137435
if (kFlutterMemoryAllocationsEnabled) {
FlutterMemoryAllocations.instance.dispatchObjectDisposed(object: this);
}
_state = null;
}