Package icyllis.modernui.fragment

Class OnBackPressedDispatcher

java.lang.Object

icyllis.modernui.fragment.OnBackPressedDispatcher

public final class OnBackPressedDispatcher
extends Object

Dispatcher that can be used to register OnBackPressedCallback instances for handling the host.onBackPressed() callback via composition.

Constructor Summary

Constructors

Constructor	Description
OnBackPressedDispatcher()	Create a new OnBackPressedDispatcher that dispatches System back button pressed events to one or more OnBackPressedCallback instances.
OnBackPressedDispatcher(Runnable fallbackOnBackPressed)	Create a new OnBackPressedDispatcher that dispatches System back button pressed events to one or more OnBackPressedCallback instances.

Method Summary

Modifier and Type	Method	Description
void	addCallback(OnBackPressedCallback onBackPressedCallback)	Add a new OnBackPressedCallback.
void	addCallback(LifecycleOwner owner, OnBackPressedCallback callback)	Receive callbacks to a new OnBackPressedCallback when the given LifecycleOwner is at least started.
boolean	hasEnabledCallbacks()	Checks if there is at least one enabled callback registered with this dispatcher.
void	onBackPressed()	Trigger a call to the currently added callbacks in reverse order in which they were added.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

OnBackPressedDispatcher

public OnBackPressedDispatcher()

Create a new OnBackPressedDispatcher that dispatches System back button pressed events to one or more OnBackPressedCallback instances.

OnBackPressedDispatcher

public OnBackPressedDispatcher(@Nullable
 Runnable fallbackOnBackPressed)

Create a new OnBackPressedDispatcher that dispatches System back button pressed events to one or more OnBackPressedCallback instances.

Parameters:

fallbackOnBackPressed - The Runnable that should be triggered if onBackPressed() is called when hasEnabledCallbacks() returns false.

Method Details

addCallback

@UiThread
public void addCallback(@Nonnull
 OnBackPressedCallback onBackPressedCallback)

Add a new OnBackPressedCallback. Callbacks are invoked in the reverse order in which they are added, so this newly added OnBackPressedCallback will be the first callback to receive a callback if onBackPressed() is called.

This method is not Lifecycle aware - if you'd like to ensure that you only get callbacks when at least started, use addCallback(LifecycleOwner, OnBackPressedCallback). It is expected that you call OnBackPressedCallback.remove() to manually remove your callback.

Parameters:

onBackPressedCallback - The callback to add

See Also:

• onBackPressed()

addCallback

@UiThread
public void addCallback(@Nonnull
 LifecycleOwner owner,
 @Nonnull
 OnBackPressedCallback callback)

Receive callbacks to a new OnBackPressedCallback when the given LifecycleOwner is at least started.

This will automatically call addCallback(OnBackPressedCallback) and remove the callback as the lifecycle state changes. As a corollary, if your lifecycle is already at least started, calling this method will result in an immediate call to addCallback(OnBackPressedCallback).

When the LifecycleOwner is destroyed, it will automatically be removed from the list of callbacks. The only time you would need to manually call OnBackPressedCallback.remove() is if you'd like to remove the callback prior to destruction of the associated lifecycle.

If the Lifecycle is already destroyed when this method is called, the callback will not be added.

Parameters:

owner - The LifecycleOwner which controls when the callback should be invoked

callback - The callback to add

See Also:

• onBackPressed()

hasEnabledCallbacks

@UiThread
public boolean hasEnabledCallbacks()

Checks if there is at least one enabled callback registered with this dispatcher.

Returns:

True if there is at least one enabled callback.

onBackPressed

@UiThread
public void onBackPressed()

Trigger a call to the currently added callbacks in reverse order in which they were added. Only if the most recently added callback is not enabled will any previously added callback be called.

If hasEnabledCallbacks() is false when this method is called, the fallback Runnable set by the constructor will be triggered.