NavigationEventDispatcher

const val PRIORITY_DEFAULT = 1: Int

Default priority level for primary UI content.

Components at this level will receive navigation events after PRIORITY_OVERLAY components have been given a chance to handle them.

const val PRIORITY_OVERLAY = 0: Int

Highest priority level, intended for overlay UI components.

Components at this level (e.g., dialogs, bottom sheets, navigation drawers) will receive navigation events before components at PRIORITY_DEFAULT.

NavigationEventDispatcher()

Creates a root NavigationEventDispatcher with no default fallback action.

Establishes the top-level dispatcher for a new navigation hierarchy, typically within an Activity or a top-level composable. It creates its own internal NavigationEventProcessor.

If a navigation event completes without being handled by any registered NavigationEventHandler, nothing further will happen.

NavigationEventDispatcher(
    onBackCompletedFallback: OnBackCompletedFallback
)

Creates a root NavigationEventDispatcher with a fallback action.

Establishes the top-level dispatcher for a new navigation hierarchy, typically within an Activity or a top-level composable. It creates its own internal NavigationEventProcessor.

NavigationEventDispatcher(parent: NavigationEventDispatcher)

Creates a child NavigationEventDispatcher linked to a parent.

Used to create nested dispatchers within an existing hierarchy. The new dispatcher shares the same underlying NavigationEventProcessor as its parent, allowing it to participate in the same event stream.

@MainThread
fun addHandler(
    handler: NavigationEventHandler<*>,
    priority: Int = PRIORITY_DEFAULT
): Unit

Adds a new NavigationEventHandler to receive navigation events.

Handlers are invoked based on priority, and then by recency. All PRIORITY_OVERLAY handlers are called before any PRIORITY_DEFAULT handlers. Within each priority group, handlers are invoked in a Last-In, First-Out (LIFO) order—the most recently added handler is called first.

All handlers are invoked on the main thread. To stop receiving events, a handler must be removed via NavigationEventHandler.remove.

@MainThread
fun addInput(input: NavigationEventInput): Unit

Adds an input with an unspecified priority, registering it with the shared processor and binding it to this dispatcher's lifecycle.

The input is registered globally with the sharedProcessor to receive system-wide state updates (e.g., whether any handlers are enabled). It is also tracked locally by this dispatcher for lifecycle management.

The input's NavigationEventInput.onAdded method is invoked immediately upon addition. It will be automatically detached when this dispatcher dispose is called.

@MainThread
fun addInput(input: NavigationEventInput, priority: Int): Unit

Adds an input with a specific priority, registering it with the shared processor and binding it to this dispatcher's lifecycle.

The input is registered globally with the sharedProcessor to receive system-wide state updates (e.g., whether any handlers are enabled). It is also tracked locally by this dispatcher for lifecycle management.

The input's NavigationEventInput.onAdded method is invoked immediately upon addition. It will be automatically detached when this dispatcher dispose is called.

@MainThread
fun dispose(): Unit

Removes this dispatcher and its entire chain of descendants from the hierarchy.

This is the primary cleanup method and should be called when the component owning this dispatcher is destroyed (e.g., in DisposableEffect in Compose).

This is a terminal operation; once a dispatcher is disposed, it cannot be reused.

Calling this method triggers a comprehensive, iterative cleanup:

1. It iteratively processes and disposes of all child dispatchers and their descendants, ensuring a complete top-down cleanup of the entire sub-hierarchy without recursion.

2. For each dispatcher, it first detaches all registered NavigationEventInput instances by calling NavigationEventInput.onRemoved. This severs their lifecycle link to the dispatcher and allows them to release any tied resources.

3. It then removes all NavigationEventHandler instances registered with that dispatcher from the shared processor, preventing memory leaks.

4. Finally, it removes the dispatcher from its parent's list of children, fully dismantling the hierarchy.

@MainThread
fun removeInput(input: NavigationEventInput): Unit

Removes and detaches an input from this dispatcher and the shared processor.

This severs the input's lifecycle link to the dispatcher. Its NavigationEventInput.onRemoved method is invoked, and it will no longer receive lifecycle calls or global state updates from the processor.

val history: StateFlow<NavigationEventHistory>

The globally observable, read-only state of the navigation history stack.

This flow represents only the navigation stack (the NavigationEventHistory.mergedHistory and NavigationEventHistory.currentIndex) and is the counterpart to transition state.

A key contract of this state is that it remains stable during a navigation gesture. It only updates when the navigation stack itself changes (e.g., when a new handler becomes active, or the active handler's info is updated), which typically occurs after a gesture completes or before one begins.

This allows UI components to subscribe only to changes in the history stack without being notified of rapid gesture progress updates from transition state.

var isEnabled: Boolean

Controls whether this dispatcher is active and will process navigation events.

A dispatcher's effective enabled state is hierarchical. It depends on both its own local isEnabled state and the state of its parent.

Getting the value:

• This will return false if the parentDispatcher exists and its isEnabled state is false, regardless of this dispatcher's own setting. This provides a simple way to disable an entire branch of a navigation hierarchy by disabling its root.

• If there is no parent or the parent is enabled, it will return the local value of this property (true by default).

Setting the value:

• This only updates the local enabled state for this specific dispatcher. The getter will always re-evaluate the effective state based on the parent.

For this dispatcher to be truly active, its local isEnabled property must be true, and the isEnabled properties of all its ancestors must also be true.

val transitionState: StateFlow<NavigationEventTransitionState>

The globally observable, read-only state of the physical navigation gesture.

This flow represents only the gesture's progress (e.g., Idle or InProgress) and is separate from the navigation history state.

System-level components or UI animations can subscribe to this flow to react to the start, progress, and end of a gesture without needing to know about the specific, generic NavigationEventInfo types involved in the history.

This state is derived from the NavigationEventTransitionState of the currently active NavigationEventHandler.