Migration guide for adding AppLifecycleState.hidden

A new hidden state was added to the AppLifecycleState enum to denote when the application is not visible.

The AppLifecycleState enum is used to indicate which lifecycle state the application is in when WidgetsBindingObserver.didChangeAppLifecycleState is called.

The new state AppLifecycleState.hidden was added to the AppLifecycleState enum in the dart:ui package.

The hidden state is entered when all of the application views are no longer visible to the user. On Android and iOS, this state is entered briefly whenever the state machine traverses from inactive to paused, or from paused to inactive. It doesn't change when paused or inactive are entered. On other platforms, it will be in this state while the application is not visible.

If code has switch statements that handle all cases of the AppLifecycleState enum, a new case will need to be added to handle the AppLifecycleState.hidden state.

Code before migration:

void didChangeAppLifecycleState(AppLifecycleState state) {
  switch (state) {
    case AppLifecycleState.resumed:
    case AppLifecycleState.inactive:
      // Do something when the app is visible...
      break;
    case AppLifecycleState.paused:
    case AppLifecycleState.detached:
      // Do something when the app is not visible...
      break;
  }
}

Code after migration:

void didChangeAppLifecycleState(AppLifecycleState state) {
  switch (state) {
    case AppLifecycleState.resumed:
    case AppLifecycleState.inactive:
      // Do something when the app is visible...
      break;
    case AppLifecycleState.hidden:  // <-- This is the new state.
    case AppLifecycleState.paused:
    case AppLifecycleState.detached:
      // Do something when the app is not visible...
      break;
  }
}

If there is already a default: case in the switch statement, or the code uses conditionals instead, then the code will compile without changes, but the default case or conditional will still need to be evaluated to decide if the hidden state should also be handled.

Landed in version: 3.11.0-16.0.pre
In stable release: 3.13.0

Relevant PRs:

• PR 42418: Adds AppLifecycleState.hidden enum value

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