dispose method

@override void dispose()

Called when this object is removed from the tree permanently.

The framework calls this method when this State object will never build again. After the framework calls dispose, the State object is considered unmounted and the mounted property is false. It is an error to call setState at this point. This stage of the lifecycle is terminal: there is no way to remount a State object that has been disposed.

Subclasses should override this method to release any resources retained by this object (e.g., stop any active animations).

If a State's build method depends on an object that can itself change state, for example a ChangeNotifier or Stream, or some other object to which one can subscribe to receive notifications, then be sure to subscribe and unsubscribe properly in initState, didUpdateWidget, and dispose:

• In initState, subscribe to the object.
• In didUpdateWidget unsubscribe from the old object and subscribe to the new one if the updated widget configuration requires replacing the object.
• In dispose, unsubscribe from the object.

Implementations of this method should end with a call to the inherited method, as in super.dispose().

Caveats

This method is not invoked at times where a developer might otherwise expect it, such as application shutdown or dismissal via platform native methods.

Application shutdown

There is no way to predict when application shutdown will happen. For example, a user's battery could catch fire, or the user could drop the device into a swimming pool, or the operating system could unilaterally terminate the application process due to memory pressure.

Applications are responsible for ensuring that they are well-behaved even in the face of a rapid unscheduled termination.

To artificially cause the entire widget tree to be disposed, consider calling runApp with a widget such as SizedBox.shrink.

To listen for platform shutdown messages (and other lifecycle changes), consider the AppLifecycleListener API.

Dismissing Flutter UI via platform native methods

An application may have both Flutter and non-Flutter UI in it. If the application calls non-Flutter methods to remove Flutter based UI such as platform native API to manipulate the platform native navigation stack, the framework does not know if the developer intends to eagerly free resources or not. The widget tree remains mounted and ready to render as soon as it is displayed again.

See the method used to bootstrap the app (e.g. runApp or runWidget) for suggestions on how to release resources more eagerly.

See also:

• deactivate, which is called prior to dispose.

Implementation

@override
void dispose() {
  if (controller != null) {
    controller!.removeListener(_onController);
  }
  super.dispose();
}