OnBackPressedDispatcher
class OnBackPressedDispatcher
Dispatcher that can be used to register OnBackPressedCallback instances for handling the ComponentActivity.onBackPressed callback via composition.
class FormEntryFragment : Fragment() {
override fun onAttach(context: Context) {
super.onAttach(context)
val callback = object : OnBackPressedCallback(
true // default to enabled
) {
override fun handleOnBackPressed() {
showAreYouSureDialog()
}
}
requireActivity().onBackPressedDispatcher.addCallback(
this, // LifecycleOwner
callback
)
}
}
When constructing an instance of this class, the fallbackOnBackPressed can be set to receive a callback if onBackPressed is called when hasEnabledCallbacks returns false.
Summary
Public constructors |
|---|
OnBackPressedDispatcher(fallbackOnBackPressed: Runnable?) |
OnBackPressedDispatcher( |
Public functions |
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Unit |
@MainThreadAdd a new |
Unit |
@MainThreadReceive callbacks to a new |
Unit |
|
Unit |
|
Unit |
|
Boolean |
Returns |
Unit |
Trigger a call to the currently added |
Unit |
@RequiresApi(value = 33)Sets the |
Extension functions |
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|---|---|
OnBackPressedCallback |
OnBackPressedDispatcher.addCallback(Create and add a new |
Public constructors
OnBackPressedDispatcher
OnBackPressedDispatcher(fallbackOnBackPressed: Runnable? = null)
OnBackPressedDispatcher
OnBackPressedDispatcher(
fallbackOnBackPressed: Runnable?,
onHasEnabledCallbacksChanged: Consumer<Boolean>?
)
Public functions
addCallback
@MainThread
fun addCallback(onBackPressedCallback: OnBackPressedCallback): Unit
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. It is expected that you call OnBackPressedCallback.remove to manually remove your callback.
| Parameters | |
|---|---|
onBackPressedCallback: OnBackPressedCallback |
The callback to add |
| See also | |
|---|---|
onBackPressed |
addCallback
@MainThread
fun addCallback(
owner: LifecycleOwner,
onBackPressedCallback: OnBackPressedCallback
): Unit
Receive callbacks to a new OnBackPressedCallback when the given LifecycleOwner is at least started.
This will automatically call addCallback 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.
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: LifecycleOwner |
The LifecycleOwner which controls when the callback should be invoked |
onBackPressedCallback: OnBackPressedCallback |
The callback to add |
| See also | |
|---|---|
onBackPressed |
dispatchOnBackCancelled
@VisibleForTesting
@MainThread
fun dispatchOnBackCancelled(): Unit
dispatchOnBackProgressed
@VisibleForTesting
@MainThread
fun dispatchOnBackProgressed(backEvent: BackEventCompat): Unit
dispatchOnBackStarted
@VisibleForTesting
@MainThread
fun dispatchOnBackStarted(backEvent: BackEventCompat): Unit
hasEnabledCallbacks
@MainThread
fun hasEnabledCallbacks(): Boolean
Returns true if there is at least one enabled callback registered with this dispatcher.
| Returns | |
|---|---|
Boolean |
True if there is at least one enabled callback. |
onBackPressed
@MainThread
fun onBackPressed(): Unit
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 fallbackOnBackPressed set by the constructor will be triggered.
setOnBackInvokedDispatcher
@RequiresApi(value = 33)
fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher): Unit
Sets the OnBackInvokedDispatcher for handling system back for Android SDK T+.
| Parameters | |
|---|---|
invoker: OnBackInvokedDispatcher |
the OnBackInvokedDispatcher to be set on this dispatcher |
Extension functions
addCallback
fun OnBackPressedDispatcher.addCallback(
owner: LifecycleOwner? = null,
enabled: Boolean = true,
onBackPressed: OnBackPressedCallback.() -> Unit
): OnBackPressedCallback
Create and add a new OnBackPressedCallback that calls onBackPressed in OnBackPressedCallback.handleOnBackPressed.
If an owner is specified, the callback will only be added when the Lifecycle is androidx.lifecycle.Lifecycle.State.STARTED.
A default enabled state can be supplied.