Merge "Make setOnBackPressedDispatcher idempotent" into androidx-main

ggfan · Jul 15, 2021 · dffae20 · dffae20
2 parents 13bf2b2 + b0af29c
commit dffae20
Show file tree

Hide file tree

Showing 2 changed files with 54 additions and 3 deletions.
diff --git a/navigation/navigation-runtime/src/androidTest/java/androidx/navigation/NavControllerTest.kt b/navigation/navigation-runtime/src/androidTest/java/androidx/navigation/NavControllerTest.kt
@@ -311,6 +311,52 @@ class NavControllerTest {
         assertThat(replacementLifecycleOwner.observerCount).isEqualTo(1)
     }
 
+    @UiThreadTest
+    @Test
+    fun testSetSameOnBackPressedDispatcher() {
+        val navController = createNavController()
+        val lifecycleOwner = TestLifecycleOwner(Lifecycle.State.RESUMED)
+        navController.setLifecycleOwner(lifecycleOwner)
+        // Set the graph and navigate to another destination to build up our back stack
+        navController.setGraph(R.navigation.nav_simple)
+        navController.navigate(R.id.second_test)
+
+        val dispatcher = OnBackPressedDispatcher()
+        navController.setOnBackPressedDispatcher(dispatcher)
+        assertThat(dispatcher.hasEnabledCallbacks()).isTrue()
+        // One observer is the NavController itself, the other is the OnBackPressedCallback
+        assertThat(lifecycleOwner.observerCount).isEqualTo(2)
+
+        navController.setOnBackPressedDispatcher(dispatcher)
+        assertThat(dispatcher.hasEnabledCallbacks()).isTrue()
+        // One observer is the NavController itself, the other is the OnBackPressedCallback
+        assertThat(lifecycleOwner.observerCount).isEqualTo(2)
+    }
+
+    @UiThreadTest
+    @Test
+    fun testSetNewOnBackPressedDispatcher() {
+        val navController = createNavController()
+        val lifecycleOwner = TestLifecycleOwner(Lifecycle.State.RESUMED)
+        navController.setLifecycleOwner(lifecycleOwner)
+        // Set the graph and navigate to another destination to build up our back stack
+        navController.setGraph(R.navigation.nav_simple)
+        navController.navigate(R.id.second_test)
+
+        val dispatcher = OnBackPressedDispatcher()
+        navController.setOnBackPressedDispatcher(dispatcher)
+        assertThat(dispatcher.hasEnabledCallbacks()).isTrue()
+        // One observer is the NavController itself, the other is the OnBackPressedCallback
+        assertThat(lifecycleOwner.observerCount).isEqualTo(2)
+
+        val replacementDispatcher = OnBackPressedDispatcher()
+        navController.setOnBackPressedDispatcher(replacementDispatcher)
+        assertThat(replacementDispatcher.hasEnabledCallbacks()).isTrue()
+        assertThat(dispatcher.hasEnabledCallbacks()).isFalse()
+        // One observer is the NavController itself, the other is the new OnBackPressedCallback
+        assertThat(lifecycleOwner.observerCount).isEqualTo(2)
+    }
+
     @UiThreadTest
     @Test
     fun testNavigate() {

diff --git a/navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt b/navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt
@@ -105,6 +105,7 @@ public open class NavController(
     private val backStackMap = mutableMapOf<Int, String?>()
     private val backStackStates = mutableMapOf<String, ArrayDeque<NavBackStackEntryState>>()
     private var lifecycleOwner: LifecycleOwner? = null
+    private var onBackPressedDispatcher: OnBackPressedDispatcher? = null
     private var viewModel: NavControllerViewModel? = null
     private val onDestinationChangedListeners = CopyOnWriteArrayList<OnDestinationChangedListener>()
 
@@ -1883,17 +1884,21 @@ public open class NavController(
     /** @suppress */
     @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
     public open fun setOnBackPressedDispatcher(dispatcher: OnBackPressedDispatcher) {
-        checkNotNull(lifecycleOwner) {
+        if (dispatcher == onBackPressedDispatcher) {
+            return
+        }
+        val lifecycleOwner = checkNotNull(lifecycleOwner) {
             "You must call setLifecycleOwner() before calling setOnBackPressedDispatcher()"
         }
         // Remove the callback from any previous dispatcher
         onBackPressedCallback.remove()
         // Then add it to the new dispatcher
-        dispatcher.addCallback(lifecycleOwner!!, onBackPressedCallback)
+        onBackPressedDispatcher = dispatcher
+        dispatcher.addCallback(lifecycleOwner, onBackPressedCallback)
 
         // Make sure that listener for updating the NavBackStackEntry lifecycles comes after
         // the dispatcher
-        lifecycleOwner!!.lifecycle.apply {
+        lifecycleOwner.lifecycle.apply {
             removeObserver(lifecycleObserver)
             addObserver(lifecycleObserver)
         }