Problem Statement
Explain the complete lifecycle of a StatefulWidget from creation to disposal, including all lifecycle methods.
Explanation
The lifecycle begins when Flutter encounters a StatefulWidget in the tree and calls createState() to create the State object. This happens only once per State object. Immediately after, initState() is called for one-time initialization like creating controllers or setting up subscriptions. You must call super.initState() first in your override.
Next, didChangeDependencies() is called automatically after initState() because dependencies are first established. This method is also called whenever InheritedWidgets that your widget depends on change. Use it for initialization requiring BuildContext or InheritedWidget access. Then build() is called to create the widget tree. Build() may be called multiple times during the widget's lifetime whenever the widget needs to rebuild.
When the parent widget rebuilds with new parameters, didUpdateWidget(oldWidget) is called before build(), allowing you to compare old and new configurations and update state accordingly. This is followed by a build() call to reflect the changes. SetState() triggers a rebuild by marking the widget dirty and scheduling a build() call.
When the widget is temporarily removed but might be reinserted (rare), deactivate() is called. If the widget is reinserted, it's reactivated; otherwise, dispose() is called for final cleanup. Dispose() is where you release resources, dispose controllers, cancel subscriptions, and remove listeners. After dispose(), the State object is removed from the tree and mounted becomes false. Always call super.dispose() last.
Understanding this lifecycle is crucial for proper resource management, avoiding memory leaks, handling async operations safely, and optimizing performance by doing work in the appropriate lifecycle method.