Factor out common traversal code in observers

Summary: Each observer was doing a similar job of traversing, and setting up child observers and its easy to not clean up child observers in some cases. This provides a helper utility for the common use case

Reviewed By: lblasa

Differential Revision: D39466930

fbshipit-source-id: e74ae5c3709297b73c020cd148a0485ac9fc0f8f

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

@@ -1,42 +1,37 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
 package com.facebook.flipper.plugins.uidebugger.litho
 
-import com.facebook.flipper.plugins.uidebugger.SubtreeUpdate
+import android.util.Log
+import com.facebook.flipper.plugins.uidebugger.LogTag
 import com.facebook.flipper.plugins.uidebugger.TreeObserver
 import com.facebook.flipper.plugins.uidebugger.core.Context
-import com.facebook.flipper.plugins.uidebugger.identityHashCode
 import com.facebook.flipper.plugins.uidebugger.observers.TreeObserverBuilder
 import com.facebook.litho.LithoView
 
 class LithoViewTreeObserver(val context: Context) : TreeObserver<LithoView>() {
 
+  override val type = "Litho"
+
   var nodeRef: LithoView? = null
+
   override fun subscribe(node: Any) {
-    node as LithoView
 
-    nodeRef = node
+    nodeRef = node as LithoView
 
-    val listener: (view: LithoView) -> Unit = {
-      val start = System.currentTimeMillis()
-
-      val (nodes, skipped) = context.layoutTraversal.traverse(it)
-
-      for (observerRoot in skipped) {
-        if (!children.containsKey(observerRoot.identityHashCode())) {
-          val observer = context.observerFactory.createObserver(observerRoot, context)!!
-          observer.subscribe(observerRoot)
-          children[observerRoot.identityHashCode()] = observer
-        }
-      }
-
-      context.treeObserverManager.emit(
-          SubtreeUpdate("Litho", nodes, start, System.currentTimeMillis()))
-    }
+    val listener: (view: LithoView) -> Unit = { traverseAndSend(context, node) }
     node.setOnDirtyMountListener(listener)
 
     listener(node)
   }
 
   override fun unsubscribe() {
+    Log.i(LogTag, "Unsubscribing from litho view")
     nodeRef?.setOnDirtyMountListener(null)
     nodeRef = null
   }

android/src/main/java/com/facebook/flipper/plugins/uidebugger/observers/ApplicationTreeObserver.kt

@@ -24,6 +24,8 @@ import com.facebook.flipper.plugins.uidebugger.identityHashCode
  */
 class ApplicationTreeObserver(val context: Context) : TreeObserver<ApplicationRef>() {
 
+  override val type = "Application"
+
   override fun subscribe(node: Any) {
     Log.i(LogTag, "subscribing to application / activity changes")
 

android/src/main/java/com/facebook/flipper/plugins/uidebugger/observers/DecorViewTreeObserver.kt

@@ -11,10 +11,8 @@ import android.util.Log
 import android.view.View
 import android.view.ViewTreeObserver
 import com.facebook.flipper.plugins.uidebugger.LogTag
-import com.facebook.flipper.plugins.uidebugger.SubtreeUpdate
 import com.facebook.flipper.plugins.uidebugger.TreeObserver
 import com.facebook.flipper.plugins.uidebugger.core.Context
-import com.facebook.flipper.plugins.uidebugger.identityHashCode
 
 typealias DecorView = View
 
@@ -23,10 +21,12 @@ class DecorViewObserver(val context: Context) : TreeObserver<DecorView>() {
 
   val throttleTimeMs = 500
 
-  // maybe should be weak reference in ctor?
+  // should this be a weak reference?
   private var nodeRef: View? = null
   private var listener: ViewTreeObserver.OnPreDrawListener? = null
 
+  override val type = "DecorView"
+
   override fun subscribe(node: Any) {
 
     node as View
@@ -38,22 +38,9 @@ class DecorViewObserver(val context: Context) : TreeObserver<DecorView>() {
         object : ViewTreeObserver.OnPreDrawListener {
           var lastSend = 0L
           override fun onPreDraw(): Boolean {
-            val start = System.currentTimeMillis()
-            if (start - lastSend > throttleTimeMs) {
-              val (nodes, skipped) = context.layoutTraversal.traverse(node)
+            if (System.currentTimeMillis() - lastSend > throttleTimeMs) {
+              traverseAndSend(context, node)
 
-              for (observerRoot in skipped) {
-
-                if (!children.containsKey(observerRoot.identityHashCode())) {
-                  val observer = context.observerFactory.createObserver(observerRoot, context)!!
-                  observer.subscribe(observerRoot)
-                  children[observerRoot.identityHashCode()] = observer
-                }
-              }
-
-              val traversalComplete = System.currentTimeMillis()
-              context.treeObserverManager.emit(
-                  SubtreeUpdate("DecorView", nodes, start, traversalComplete))
               lastSend = System.currentTimeMillis()
             }
             return true
@@ -64,11 +51,9 @@ class DecorViewObserver(val context: Context) : TreeObserver<DecorView>() {
   }
 
   override fun unsubscribe() {
-    Log.i(LogTag, "Try Unsubscribing to decor view changes")
+    Log.i(LogTag, "Unsubscribing from decor view changes")
 
     listener.let {
-      Log.i(LogTag, "Actually Unsubscribing to decor view changes")
-
       nodeRef?.viewTreeObserver?.removeOnPreDrawListener(it)
       listener = null
       nodeRef = null

android/src/main/java/com/facebook/flipper/plugins/uidebugger/observers/TreeObserver.kt

@@ -103,7 +103,7 @@ It is responsible for:
  1. listening to the relevant framework events
  2. Traversing the hierarchy of the managed nodes
  3. Diffing to previous state (optional)
- 4. Pushing out updates for its entire set of nodes
+ 4. Pushing out updates for its entire set of managed nodes
 
  If while traversing it encounters a node type which has its own TreeObserver, it
  does not traverse that, instead it sets up a Tree observer responsible for that subtree
@@ -114,12 +114,51 @@ abstract class TreeObserver<T> {
 
   protected val children: MutableMap<Int, TreeObserver<*>> = mutableMapOf()
 
-  // todo try to pass T again?
+  abstract val type: String
+
   abstract fun subscribe(node: Any)
 
   abstract fun unsubscribe()
 
+  /**
+   * Optional helper method that traverses the layout hierarchy while managing any encountered child
+   * observers correctly
+   */
+  fun traverseAndSend(context: Context, root: Any) {
+    val start = System.currentTimeMillis()
+    val (visitedNodes, observerRootsNodes) = context.layoutTraversal.traverse(root)
+
+    // Add any new Observers
+    for (observerRoot in observerRootsNodes) {
+
+      if (!children.containsKey(observerRoot.identityHashCode())) {
+        val childObserver = context.observerFactory.createObserver(observerRoot, context)!!
+        Log.d(
+            LogTag,
+            "For Observer ${this.type} discovered new child of type ${childObserver.type} Node ID ${observerRoot.identityHashCode()}")
+        childObserver.subscribe(observerRoot)
+        children[observerRoot.identityHashCode()] = childObserver
+      }
+    }
+
+    // remove any old observers
+    val observerRootIds = observerRootsNodes.map { it.identityHashCode() }
+    for (childKey in children.keys) {
+      if (!observerRootIds.contains(childKey)) {
+
+        Log.d(
+            LogTag,
+            "For Observer ${this.type} cleaning up child of type ${children[childKey]!!.type} Node ID ${childKey}")
+
+        children[childKey]!!.cleanUpRecursive()
+      }
+    }
+    context.treeObserverManager.emit(
+        SubtreeUpdate(type, visitedNodes, start, System.currentTimeMillis()))
+  }
+
   fun cleanUpRecursive() {
+    Log.i(LogTag, "Cleaning up observer ${this}")
     children.values.forEach { it.cleanUpRecursive() }
     unsubscribe()
     children.clear()
@@ -192,7 +231,6 @@ class PartialLayoutTraversal(
         val attributes = mutableMapOf<String, InspectableObject>()
         descriptor.getData(node, attributes)
 
-        // NOTE active child null here
         visited.add(
             Node(
                 descriptor.getId(node),