New OnBackEffect

To detect back pressed, but not consume it.

Fix: 312638864
Test: unit test
Change-Id: I28abb1d84f615bc8ca51aa883ca14d728e2d8bb5

2 files changed, 147 insertions, 0 deletions

diff --git a/packages/SettingsLib/Spa/spa/src/com/android/settingslib/spa/framework/compose/OnBackEffect.kt b/packages/SettingsLib/Spa/spa/src/com/android/settingslib/spa/framework/compose/OnBackEffect.kt
new file mode 100644
index 000000000000..3991f26e1b0c
--- /dev/null
+++ b/packages/SettingsLib/Spa/spa/src/com/android/settingslib/spa/framework/compose/OnBackEffect.kt
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settingslib.spa.framework.compose
+
+import androidx.activity.OnBackPressedCallback
+import androidx.activity.OnBackPressedDispatcher
+import androidx.activity.compose.LocalOnBackPressedDispatcherOwner
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberUpdatedState
+import androidx.compose.ui.platform.LocalLifecycleOwner
+
+/**
+ * An effect for detecting presses of the system back button, and the back event will not be
+ * consumed by this effect.
+ *
+ * Calling this in your composable adds the given lambda to the [OnBackPressedDispatcher] of the
+ * [LocalOnBackPressedDispatcherOwner].
+ *
+ * @param onBack the action invoked by pressing the system back
+ */
+@Composable
+fun OnBackEffect(onBack: () -> Unit) {
+    val backDispatcher = checkNotNull(LocalOnBackPressedDispatcherOwner.current) {
+        "No OnBackPressedDispatcherOwner was provided via LocalOnBackPressedDispatcherOwner"
+    }.onBackPressedDispatcher
+
+    // Safely update the current `onBack` lambda when a new one is provided
+    val currentOnBack by rememberUpdatedState(onBack)
+    // Remember in Composition a back callback that calls the `onBack` lambda
+    val backCallback = remember {
+        object : OnBackPressedCallback(true) {
+            override fun handleOnBackPressed() {
+                remove()
+                currentOnBack()
+                backDispatcher.onBackPressed()
+            }
+        }
+    }
+    val lifecycleOwner = LocalLifecycleOwner.current
+    DisposableEffect(lifecycleOwner, backDispatcher) {
+        // Add callback to the backDispatcher
+        backDispatcher.addCallback(lifecycleOwner, backCallback)
+        // When the effect leaves the Composition, remove the callback
+        onDispose {
+            backCallback.remove()
+        }
+    }
+}
diff --git a/packages/SettingsLib/Spa/tests/src/com/android/settingslib/spa/framework/compose/OnBackEffectTest.kt b/packages/SettingsLib/Spa/tests/src/com/android/settingslib/spa/framework/compose/OnBackEffectTest.kt
new file mode 100644
index 000000000000..588168636828
--- /dev/null
+++ b/packages/SettingsLib/Spa/tests/src/com/android/settingslib/spa/framework/compose/OnBackEffectTest.kt
@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settingslib.spa.framework.compose
+
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.ui.test.hasText
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.android.settingslib.spa.testutils.waitUntilExists
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.delay
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(AndroidJUnit4::class)
+class OnBackEffectTest {
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    private var onBackEffectCalled = false
+
+    @Test
+    fun onBackEffect() {
+        composeTestRule.setContent {
+            TestNavHost {
+                val navController = LocalNavController.current
+                LaunchedEffect(Unit) {
+                    navController.navigate(ROUTE_B)
+                    delay(100)
+                    navController.navigateBack()
+                }
+            }
+        }
+
+        composeTestRule.waitUntilExists(hasText(ROUTE_A))
+        assertThat(onBackEffectCalled).isTrue()
+    }
+
+    @Composable
+    private fun TestNavHost(content: @Composable () -> Unit) {
+        val navController = rememberNavController()
+        CompositionLocalProvider(navController.localNavController()) {
+            NavHost(navController, ROUTE_A) {
+                composable(route = ROUTE_A) { Text(ROUTE_A) }
+                composable(route = ROUTE_B) {
+                    Text(ROUTE_B)
+
+                    OnBackEffect {
+                        onBackEffectCalled = true
+                    }
+                }
+            }
+            content()
+        }
+    }
+
+    private companion object {
+        const val ROUTE_A = "RouteA"
+        const val ROUTE_B = "RouteB"
+    }
+}