Add ability to unmounted on detached from window

Summary: Add ability to unmount any left over items on detached from window.

Reviewed By: adityasharat

Differential Revision: D55342976

fbshipit-source-id: f23cc5ad4cd29bdefaec109183ccb7b666edfac8

litho-core/src/main/java/com/facebook/litho/LithoView.java

@@ -706,6 +706,10 @@ protected void onDetached() {
     super.onDetached();
     if (mComponentTree != null) {
       mComponentTree.detach();
+
+      if (mComponentTree.getLithoConfiguration().componentsConfig.unmountOnDetachedFromWindow) {
+        unmountAllItems();
+      }
     }
 
     AccessibilityManagerCompat.removeAccessibilityStateChangeListener(

litho-core/src/main/java/com/facebook/litho/config/ComponentsConfiguration.kt

@@ -63,6 +63,14 @@ internal constructor(
      */
     @JvmField
     val shouldNotifyVisibleBoundsChangeWhenNestedLithoViewBecomesInvisible: Boolean = false,
+    /**
+     * If enabled, then the [com.facebook.litho.LithoView] will attempt to unmount any mounted
+     * content of the mount state when it gets detached from window.
+     *
+     * This is done to tackle and edge case where mount contents that have the same top/bottom
+     * boundaries of the host view are not mounted by incremental mount.
+     */
+    @JvmField val unmountOnDetachedFromWindow: Boolean = false,
     /** Whether the [ComponentTree] should be using State Reconciliation. */
     @JvmField val isReconciliationEnabled: Boolean = true,
     /** The handler [ComponentTree] will be used to run the pre-allocation process */
@@ -283,6 +291,7 @@ internal constructor(
     private var shouldBuildRenderTreeInBg = baseConfig.shouldBuildRenderTreeInBg
     private var enablePreAllocationSameThreadCheck = baseConfig.enablePreAllocationSameThreadCheck
     private var avoidRedundantPreAllocations = baseConfig.avoidRedundantPreAllocations
+    private var unmountOnDetachedFromWindow = baseConfig.unmountOnDetachedFromWindow
 
     fun shouldNotifyVisibleBoundsChangeWhenNestedLithoViewBecomesInvisible(
         enabled: Boolean
@@ -360,6 +369,10 @@ internal constructor(
       avoidRedundantPreAllocations = value
     }
 
+    fun unmountOnDetachedFromWindow(unmountOnDetachedFromWindow: Boolean): Builder = also {
+      this.unmountOnDetachedFromWindow = unmountOnDetachedFromWindow
+    }
+
     fun build(): ComponentsConfiguration {
       return baseConfig.copy(
           specsApiStateUpdateDuplicateDetectionEnabled =
@@ -390,7 +403,7 @@ internal constructor(
           shouldReuseIdToPositionMap = shouldBuildRenderTreeInBg,
           enablePreAllocationSameThreadCheck = enablePreAllocationSameThreadCheck,
           avoidRedundantPreAllocations = avoidRedundantPreAllocations,
-      )
+          unmountOnDetachedFromWindow = unmountOnDetachedFromWindow)
     }
   }
 }

litho-it/src/test/java/com/facebook/litho/UnmountOnDetachTest.kt

@@ -0,0 +1,125 @@
+// (c) Meta Platforms, Inc. and affiliates. Confidential and proprietary.
+
+package com.facebook.litho
+
+import android.content.Context
+import android.view.View
+import com.facebook.litho.binders.viewBinder
+import com.facebook.litho.config.ComponentsConfiguration
+import com.facebook.litho.kotlin.widget.Text
+import com.facebook.litho.testing.LithoViewRule
+import com.facebook.litho.testing.assertj.LithoAssertions
+import com.facebook.litho.testing.testrunner.LithoTestRunner
+import com.facebook.rendercore.RenderUnit
+import org.assertj.core.api.Assertions
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/**
+ * This test focuses on testing the behavior around
+ * [ComponentsConfiguration.unmountOnDetachedFromWindow].
+ */
+@RunWith(LithoTestRunner::class)
+class UnmountOnDetachTest {
+
+  @get:Rule val lithoRule = LithoViewRule()
+
+  @Test
+  fun `should not unmount on detach when unmount on detach is disabled`() {
+    var mountCount = 0
+    var unmountCount = 0
+    val component =
+        UnmountOnDetachComponent(
+            "Mount Text", onBind = { mountCount++ }, onUnbind = { unmountCount++ })
+
+    val lithoView =
+        lithoRule.render(
+            componentTree =
+                ComponentTree.create(lithoRule.context)
+                    .componentsConfiguration(
+                        ComponentsConfiguration.defaultInstance.copy(
+                            unmountOnDetachedFromWindow = false))
+                    .build()) {
+              component
+            }
+
+    LithoAssertions.assertThat(lithoView).hasVisibleText("Mount Text")
+
+    lithoView.detachFromWindow()
+
+    Assertions.assertThat(mountCount).isEqualTo(1)
+    Assertions.assertThat(unmountCount).isEqualTo(0)
+  }
+
+  @Test
+  fun `should unmount on detach when unmount on detach is enabled`() {
+    var mountCount = 0
+    var unmountCount = 0
+    val component =
+        UnmountOnDetachComponent(
+            "Mount Text", onBind = { mountCount++ }, onUnbind = { unmountCount++ })
+
+    val lithoView =
+        lithoRule.render(
+            componentTree =
+                ComponentTree.create(lithoRule.context)
+                    .componentsConfiguration(
+                        ComponentsConfiguration.defaultInstance.copy(
+                            unmountOnDetachedFromWindow = true))
+                    .build()) {
+              component
+            }
+
+    LithoAssertions.assertThat(lithoView).hasVisibleText("Mount Text")
+
+    lithoView.detachFromWindow()
+
+    Assertions.assertThat(mountCount).isEqualTo(1)
+    Assertions.assertThat(unmountCount).isEqualTo(1)
+  }
+
+  private class UnmountOnDetachComponent(
+      private val name: String,
+      private val onBind: () -> Unit,
+      private val onUnbind: () -> Unit
+  ) : KComponent() {
+
+    override fun ComponentScope.render(): Component? {
+      return Text(
+          text = name,
+          style =
+              Style.viewBinder(
+                  RenderUnit.DelegateBinder.createDelegateBinder(
+                      Unit,
+                      object : RenderUnit.Binder<Any, View, Any> {
+                        override fun shouldUpdate(
+                            currentModel: Any,
+                            newModel: Any,
+                            currentLayoutData: Any?,
+                            nextLayoutData: Any?
+                        ): Boolean = false
+
+                        override fun bind(
+                            context: Context,
+                            content: View,
+                            model: Any,
+                            layoutData: Any?
+                        ): Any? {
+                          onBind()
+                          return Unit
+                        }
+
+                        override fun unbind(
+                            context: Context,
+                            content: View,
+                            model: Any,
+                            layoutData: Any?,
+                            bindData: Any?
+                        ) {
+                          onUnbind()
+                        }
+                      })))
+    }
+  }
+}

litho-testing/src/main/java/com/facebook/litho/testing/testrunner/LithoTestRunner.java

@@ -73,7 +73,7 @@ public LithoTestRunner(final Class<?> testClass) throws InitializationError {
    *     configurations.
    */
   private List<? extends Class<? extends LithoTestRunConfiguration>> getGlobalConfigs() {
-    return Arrays.asList();
+    return Arrays.asList(UnmountOnDetachConfiguration.class);
   }
 
   @Override

litho-testing/src/main/java/com/facebook/litho/testing/testrunner/UnmountOnDetachConfiguration.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * 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.facebook.litho.testing.testrunner
+
+import com.facebook.litho.config.ComponentsConfiguration
+import org.junit.runners.model.FrameworkMethod
+
+class UnmountOnDetachConfiguration : LithoTestRunConfiguration {
+
+  private val defaultInstance = ComponentsConfiguration.defaultInstance
+
+  override fun beforeTest(method: FrameworkMethod) {
+    ComponentsConfiguration.defaultInstance =
+        defaultInstance.copy(unmountOnDetachedFromWindow = true)
+  }
+
+  override fun afterTest(method: FrameworkMethod) {
+    ComponentsConfiguration.defaultInstance = defaultInstance
+  }
+}