Only send layout update operation to nativehierarchymanager when layout actually changes.

Reviewed By: andreicoman11

Differential Revision: D2679408

fb-gh-sync-id: 7f0a972e9e12f70402e2d285edef458a61ca1c39

ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactShadowNode.java

@@ -18,6 +18,7 @@ import com.facebook.csslayout.CSSNode;
 import com.facebook.infer.annotation.Assertions;
 import com.facebook.react.bridge.ReadableMap;
 import com.facebook.react.bridge.ReadableMapKeySetIterator;
+import com.facebook.react.uimanager.events.EventDispatcher;
 
 /**
  * Base node class for representing virtual tree of React nodes. Shadow nodes are used primarily
@@ -202,18 +203,37 @@ public class ReactShadowNode extends CSSNode {
       float absoluteX,
       float absoluteY,
       UIViewOperationQueue uiViewOperationQueue,
-      NativeViewHierarchyOptimizer nativeViewHierarchyOptimizer) {
+      NativeViewHierarchyOptimizer nativeViewHierarchyOptimizer,
+      EventDispatcher eventDispatcher) {
     if (mNodeUpdated) {
       onCollectExtraUpdates(uiViewOperationQueue);
     }
 
     if (hasNewLayout()) {
-      mAbsoluteLeft = Math.round(absoluteX + getLayoutX());
-      mAbsoluteTop = Math.round(absoluteY + getLayoutY());
-      mAbsoluteRight = Math.round(absoluteX + getLayoutX() + getLayoutWidth());
-      mAbsoluteBottom = Math.round(absoluteY + getLayoutY() + getLayoutHeight());
+      float absoluteLeft = Math.round(absoluteX + getLayoutX());
+      float absoluteTop = Math.round(absoluteY + getLayoutY());
+      float absoluteRight = Math.round(absoluteX + getLayoutX() + getLayoutWidth());
+      float absoluteBottom = Math.round(absoluteY + getLayoutY() + getLayoutHeight());
+      // If the layout didn't change this should calculate exactly same values, it's fine to compare
+      // floats with "==" in this case
+      if (absoluteLeft != mAbsoluteLeft || absoluteTop != mAbsoluteTop ||
+          absoluteRight != mAbsoluteRight || absoluteBottom != mAbsoluteBottom) {
+        mAbsoluteLeft = absoluteLeft;
+        mAbsoluteTop = absoluteTop;
+        mAbsoluteRight = absoluteRight;
+        mAbsoluteBottom = absoluteBottom;
 
-      nativeViewHierarchyOptimizer.handleUpdateLayout(this);
+        nativeViewHierarchyOptimizer.handleUpdateLayout(this);
+        if (mShouldNotifyOnLayout) {
+          eventDispatcher.dispatchEvent(
+              OnLayoutEvent.obtain(
+                  getReactTag(),
+                  getScreenX(),
+                  getScreenY(),
+                  getScreenWidth(),
+                  getScreenHeight()));
+        }
+      }
     }
   }
 
@@ -264,10 +284,6 @@ public class ReactShadowNode extends CSSNode {
     mShouldNotifyOnLayout = shouldNotifyOnLayout;
   }
 
-  /* package */ boolean shouldNotifyOnLayout() {
-    return mShouldNotifyOnLayout;
-  }
-
   /**
    * Adds a child that the native view hierarchy will have at this index in the native view
    * corresponding to this node.

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModule.java

@@ -814,18 +814,8 @@ public class UIManagerModule extends ReactContextBaseJavaModule implements
           absoluteX,
           absoluteY,
           mOperationsQueue,
-          mNativeViewHierarchyOptimizer);
-
-      // notify JS about layout event if requested
-      if (cssNode.shouldNotifyOnLayout()) {
-        mEventDispatcher.dispatchEvent(
-            OnLayoutEvent.obtain(
-                tag,
-                cssNode.getScreenX(),
-                cssNode.getScreenY(),
-                cssNode.getScreenWidth(),
-                cssNode.getScreenHeight()));
-      }
+          mNativeViewHierarchyOptimizer,
+          mEventDispatcher);
     }
     cssNode.markUpdateSeen();
   }