dispose method
The framework calls this method when this StateX object will never build again. Note: YOU WILL HAVE NO IDEA WHEN THIS WILL RUN in the Framework.
Implementation
@mustCallSuper
void dispose() {
/// The framework calls this method when this [StateX] object will never
/// build again. The [State] object's lifecycle is terminated.
/// Subclasses should override this method to release any resources retained
/// by this object (e.g., stop any active animations).
}