Use mount extension for litho integration

Summary:
Initial implementation of Litho extensions using mount extension. After mount is called on the main thread and we traverse the hierachy. In future we can use mount extensions to construct a sparse tree rather  than sending everything every time.

Scroll is handled with a native UI scroll listener for each litho view. This may break if the litho view is not a direct child of the scroll view.

Reviewed By: mihaelao

Differential Revision: D40021840

fbshipit-source-id: b09086a7a16660225885620609009dddf5b90d3b

android/plugins/litho/build.gradle

@@ -20,6 +20,7 @@ android {
     dependencies {
         compileOnly deps.lithoAnnotations
         implementation project(':android')
+        implementation deps.kotlinCoroutinesAndroid
         implementation deps.lithoCore
         api deps.lithoEditorCore
         api(deps.lithoEditorFlipper) {

android/plugins/litho/src/main/java/com/facebook/flipper/plugins/uidebugger/litho/LithoObserver.kt

@@ -8,38 +8,92 @@
 package com.facebook.flipper.plugins.uidebugger.litho
 
 import android.util.Log
+import android.view.ViewTreeObserver
 import com.facebook.flipper.plugins.uidebugger.LogTag
 import com.facebook.flipper.plugins.uidebugger.core.Context
 import com.facebook.flipper.plugins.uidebugger.descriptors.nodeId
 import com.facebook.flipper.plugins.uidebugger.observers.TreeObserver
 import com.facebook.flipper.plugins.uidebugger.observers.TreeObserverBuilder
+import com.facebook.flipper.plugins.uidebugger.scheduler.throttleLatest
 import com.facebook.litho.LithoView
+import com.facebook.rendercore.extensions.ExtensionState
+import com.facebook.rendercore.extensions.MountExtension
+import kotlinx.coroutines.*
 
+/**
+ * There are 2 ways a litho view can update:
+ * 1. a view was added / updated / removed through a mount ,we use the mount extension to capture
+ * these
+ * 2. The user scrolled. This does not cause a mount to the litho view but it may cause new
+ * components to mount as they come on screen On the native side we capture scrolls as it causes the
+ * draw listener to first but but the layout traversal would stop once it sees the lithoview.
+ *
+ * Therefore we need a way to capture the changes in the position of views in a litho view hierarchy
+ * as they are scrolled. A property that seems to hold for litho is if there is a scrolling view in
+ * the heierachy, its direct children are lithoview.
+ *
+ * Given that we are observing a litho view in this class for mount extension we can also attach a
+ * on scroll changed listener to it to be notified by android when it is scrolled. We just need to
+ * then update the bounds for this view as nothing else has changed. If this scroll does lead to a
+ * mount this will be picked up by the mount extension
+ */
 class LithoViewTreeObserver(val context: Context) : TreeObserver<LithoView>() {
 
   override val type = "Litho"
+  private val throttleTimeMs = 500L
 
-  private var nodeRef: LithoView? = null
+  private val waitScope = CoroutineScope(Dispatchers.IO)
+  private val mainScope = CoroutineScope(Dispatchers.Main)
+  var nodeRef: LithoView? = null
+  var onScrollChangedListener: ViewTreeObserver.OnScrollChangedListener? = null
 
   override fun subscribe(node: Any) {
 
-    Log.i(LogTag, "Subscribing to litho view ${node.nodeId()}")
+    Log.d(LogTag, "Subscribing to litho view ${node.nodeId()}")
 
     nodeRef = node as LithoView
 
-    val listener: (view: LithoView) -> Unit = { processUpdate(context, node) }
-    node.setOnDirtyMountListener(listener)
+    val lithoDebuggerExtension = LithoDebuggerExtension(this)
+    node.registerUIDebugger(lithoDebuggerExtension)
 
-    listener(node)
+    val throttledUpdate =
+        throttleLatest<Any>(throttleTimeMs, waitScope, mainScope) { node ->
+          // todo only send bounds for the view rather than the entire hierachy
+          processUpdate(context, node)
+        }
+
+    onScrollChangedListener = ViewTreeObserver.OnScrollChangedListener({ throttledUpdate(node) })
+    node.viewTreeObserver.addOnScrollChangedListener(onScrollChangedListener)
+
+    // we have already missed the first mount so we trigger it manually on subscribe
+    processUpdate(context, node)
   }
 
   override fun unsubscribe() {
-    Log.i(LogTag, "Unsubscribing from litho view")
-    nodeRef?.setOnDirtyMountListener(null)
+    Log.d(LogTag, "Unsubscribing from litho view ${nodeRef?.nodeId()}")
+    nodeRef?.viewTreeObserver?.removeOnScrollChangedListener(onScrollChangedListener)
+    nodeRef?.unregisterUIDebugger()
     nodeRef = null
   }
 }
 
+class LithoDebuggerExtension(val observer: LithoViewTreeObserver) : MountExtension<Void?, Void?>() {
+
+  override fun createState(): Void? {
+    return null
+  }
+
+  /**
+   * The call guaranteed to be called after new layout mounted completely on the main thread.
+   * mounting includes adding updating or removing views from the heriachy
+   */
+  override fun afterMount(state: ExtensionState<Void?>) {
+    Log.i(LogTag, "After mount called for litho view ${observer.nodeRef?.nodeId()}")
+    // todo sparse update
+    observer.processUpdate(observer.context, state.rootHost as Any)
+  }
+}
+
 object LithoViewTreeObserverBuilder : TreeObserverBuilder<LithoView> {
   override fun canBuildFor(node: Any): Boolean {
     return node is LithoView

gradle.properties

@@ -2,7 +2,6 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
 # POM publishing constants
 VERSION_NAME=0.171.2-SNAPSHOT
 GROUP=com.facebook.flipper
@@ -17,18 +16,15 @@ POM_LICENCE_DIST=repo
 POM_DEVELOPER_ID=facebook
 POM_DEVELOPER_NAME=facebook
 POM_ISSUES_URL=https://github.com/facebook/flipper/issues/
-
 # Shared version numbers
-LITHO_VERSION=0.41.1
+LITHO_VERSION=0.43.0
 ANDROIDX_VERSION=1.3.0
 KOTLIN_VERSION=1.6.20
-
 # Gradle internals
 org.gradle.internal.repository.max.retries=10
 org.gradle.internal.repository.initial.backoff=1250
 org.gradle.jvmargs=-Xmx2g -Xms512m -XX:MaxPermSize=1024m -XX:+CMSClassUnloadingEnabled
 systemProp.org.gradle.internal.http.connectionTimeout=120000
 systemProp.org.gradle.internal.http.socketTimeout=120000
-
 android.useAndroidX=true
 android.enableJetifier=true