Android Paper top-down onLayout events

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactShadowNode.java

@@ -123,9 +123,9 @@ public interface ReactShadowNode<T extends ReactShadowNode> {
    */
   void onCollectExtraUpdates(UIViewOperationQueue uiViewOperationQueue);
 
-  /** @return true if layout (position or dimensions) changed, false otherwise. */
+  /* package */ boolean dispatchUpdatesWillChangeLayout(float absoluteX, float absoluteY);
 
-  /* package */ boolean dispatchUpdates(
+  /* package */ void dispatchUpdates(
       float absoluteX,
       float absoluteY,
       UIViewOperationQueue uiViewOperationQueue,

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactShadowNodeImpl.java

@@ -337,9 +337,32 @@ public void onAfterUpdateTransaction() {
   @Override
   public void onCollectExtraUpdates(UIViewOperationQueue uiViewOperationQueue) {}
 
-  /** @return true if layout (position or dimensions) changed, false otherwise. */
   @Override
-  public boolean dispatchUpdates(
+  public boolean dispatchUpdatesWillChangeLayout(float absoluteX, float absoluteY) {
+    if (!hasNewLayout()) {
+      return false;
+    }
+
+    float layoutX = getLayoutX();
+    float layoutY = getLayoutY();
+    int newAbsoluteLeft = Math.round(absoluteX + layoutX);
+    int newAbsoluteTop = Math.round(absoluteY + layoutY);
+    int newAbsoluteRight = Math.round(absoluteX + layoutX + getLayoutWidth());
+    int newAbsoluteBottom = Math.round(absoluteY + layoutY + getLayoutHeight());
+
+    int newScreenX = Math.round(layoutX);
+    int newScreenY = Math.round(layoutY);
+    int newScreenWidth = newAbsoluteRight - newAbsoluteLeft;
+    int newScreenHeight = newAbsoluteBottom - newAbsoluteTop;
+
+    return newScreenX != mScreenX
+        || newScreenY != mScreenY
+        || newScreenWidth != mScreenWidth
+        || newScreenHeight != mScreenHeight;
+  }
+
+  @Override
+  public void dispatchUpdates(
       float absoluteX,
       float absoluteY,
       UIViewOperationQueue uiViewOperationQueue,
@@ -386,10 +409,6 @@ public boolean dispatchUpdates(
               getScreenHeight());
         }
       }
-
-      return layoutHasChanged;
-    } else {
-      return false;
     }
   }
 

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/UIImplementation.java

@@ -29,7 +29,9 @@
 import com.facebook.systrace.SystraceMessage;
 import com.facebook.yoga.YogaConstants;
 import com.facebook.yoga.YogaDirection;
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.List;
 import java.util.Map;
 
 /**
@@ -665,7 +667,20 @@ protected void updateViewHierarchy() {
               .arg("rootTag", cssRoot.getReactTag())
               .flush();
           try {
-            applyUpdatesRecursive(cssRoot, 0f, 0f);
+            List<ReactShadowNode> onLayoutNodes = new ArrayList<>();
+            applyUpdatesRecursive(cssRoot, 0f, 0f, onLayoutNodes);
+
+            for (ReactShadowNode node : onLayoutNodes) {
+              mEventDispatcher.dispatchEvent(
+                  OnLayoutEvent.obtain(
+                      -1, /* surfaceId not used in classic renderer */
+                      node.getReactTag(),
+                      node.getScreenX(),
+                      node.getScreenY(),
+                      node.getScreenWidth(),
+                      node.getScreenHeight()));
+            }
+
           } finally {
             Systrace.endSection(Systrace.TRACE_TAG_REACT_JAVA_BRIDGE);
           }
@@ -951,39 +966,34 @@ protected void calculateRootLayout(ReactShadowNode cssRoot) {
     }
   }
 
-  protected void applyUpdatesRecursive(ReactShadowNode cssNode, float absoluteX, float absoluteY) {
+  protected void applyUpdatesRecursive(
+      ReactShadowNode cssNode,
+      float absoluteX,
+      float absoluteY,
+      List<ReactShadowNode> onLayoutNodes) {
     if (!cssNode.hasUpdates()) {
       return;
     }
 
+    if (cssNode.dispatchUpdatesWillChangeLayout(absoluteX, absoluteY)
+        && cssNode.shouldNotifyOnLayout()
+        && !mShadowNodeRegistry.isRootNode(cssNode.getReactTag())) {
+      onLayoutNodes.add(cssNode);
+    }
+
     Iterable<? extends ReactShadowNode> cssChildren = cssNode.calculateLayoutOnChildren();
     if (cssChildren != null) {
       for (ReactShadowNode cssChild : cssChildren) {
         applyUpdatesRecursive(
-            cssChild, absoluteX + cssNode.getLayoutX(), absoluteY + cssNode.getLayoutY());
+            cssChild,
+            absoluteX + cssNode.getLayoutX(),
+            absoluteY + cssNode.getLayoutY(),
+            onLayoutNodes);
       }
     }
 
-    int tag = cssNode.getReactTag();
-    if (!mShadowNodeRegistry.isRootNode(tag)) {
-      boolean frameDidChange =
-          cssNode.dispatchUpdates(
-              absoluteX, absoluteY, mOperationsQueue, mNativeViewHierarchyOptimizer);
-
-      // Notify JS about layout event if requested
-      // and if the position or dimensions actually changed
-      // (consistent with iOS).
-      if (frameDidChange && cssNode.shouldNotifyOnLayout()) {
-        mEventDispatcher.dispatchEvent(
-            OnLayoutEvent.obtain(
-                -1, /* surfaceId not used in classic renderer */
-                tag,
-                cssNode.getScreenX(),
-                cssNode.getScreenY(),
-                cssNode.getScreenWidth(),
-                cssNode.getScreenHeight()));
-      }
-    }
+    cssNode.dispatchUpdates(absoluteX, absoluteY, mOperationsQueue, mNativeViewHierarchyOptimizer);
+
     cssNode.markUpdateSeen();
     mNativeViewHierarchyOptimizer.onViewUpdatesCompleted(cssNode);
   }