OnBackInvokedDispatcher

PRIORITY_DEFAULT

static val PRIORITY_DEFAULT: Int

Default priority level of OnBackInvokedCallbacks.

Value: 0

PRIORITY_OVERLAY

static val PRIORITY_OVERLAY: Int

Priority level of OnBackInvokedCallbacks for overlays such as menus and navigation drawers that should receive back dispatch before non-overlays.

Value: 1000000

PRIORITY_SYSTEM_NAVIGATION_OBSERVER

static val PRIORITY_SYSTEM_NAVIGATION_OBSERVER: Int

Priority level of OnBackInvokedCallbacks designed to observe system-level back handling.

Callbacks registered with this priority are invoked only when a back event is not consumed by any other registered OnBackInvokedCallback with a priority of PRIORITY_DEFAULT or higher. This means they are called when the system is about to perform its default back navigation action, such as finishing the current activity or executing a back-to-home animation.

These callbacks are purely observational. They do not consume the back event and cannot intercept it. Their invocation has no impact on the normal back navigation flow, making them suitable for logging, analytics, or triggering actions that should not prevent the system's own back handling.

The invocation order for multiple callbacks registered with this priority is undefined.

On API level 36 only, there is a restriction that only one callback with PRIORITY_SYSTEM_NAVIGATION_OBSERVER can be registered at a time. On API level 37 and higher, the number of registered observer callbacks is unrestricted.

Value: -2

registerOnBackInvokedCallback

abstract fun registerOnBackInvokedCallback(
    priority: Int, 
    callback: OnBackInvokedCallback
): Unit

Registers a OnBackInvokedCallback. Within the same priority level, callbacks are invoked in the reverse order in which they are registered. Higher priority callbacks are invoked before lower priority ones.

unregisterOnBackInvokedCallback

abstract fun unregisterOnBackInvokedCallback(callback: OnBackInvokedCallback): Unit

Unregisters a OnBackInvokedCallback.