track previous contentOffset to avoid duplicate calls

Summary:
- there was a bug when `contentOffset` was set to {x:0, y:0} and there were items lazy loaded in with prop changes- the View would consistently scroll back to the top after loading in new items
- to avoid this, we store the offset value when it's first set, and only run the `scrollTo` logic then

Changelog:
[Internal][Fixed] - Fix contentOffset forcing scroll to top behavior

Reviewed By: fkgozali, mdvacca

Differential Revision: D42089871

fbshipit-source-id: 3968d98341728a45bec28e8783c9977e91dd4d2c

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java

@@ -33,9 +33,11 @@
 import com.facebook.common.logging.FLog;
 import com.facebook.infer.annotation.Assertions;
 import com.facebook.react.R;
+import com.facebook.react.bridge.ReadableMap;
 import com.facebook.react.common.ReactConstants;
 import com.facebook.react.uimanager.FabricViewStateManager;
 import com.facebook.react.uimanager.MeasureSpecAssertions;
+import com.facebook.react.uimanager.PixelUtil;
 import com.facebook.react.uimanager.PointerEvents;
 import com.facebook.react.uimanager.ReactClippingViewGroup;
 import com.facebook.react.uimanager.ReactClippingViewGroupHelper;
@@ -100,6 +102,7 @@ public class ReactScrollView extends ScrollView
   private int mSnapToAlignment = SNAP_ALIGNMENT_DISABLED;
   private @Nullable View mContentView;
   private ReactViewBackgroundManager mReactBackgroundManager;
+  private @Nullable ReadableMap mCurrentContentOffset = null;
   private int pendingContentOffsetX = UNSET_CONTENT_OFFSET;
   private int pendingContentOffsetY = UNSET_CONTENT_OFFSET;
   private final FabricViewStateManager mFabricViewStateManager = new FabricViewStateManager();
@@ -1002,6 +1005,23 @@ public void onChildViewRemoved(View parent, View child) {
     mContentView = null;
   }
 
+  public void setContentOffset(ReadableMap value) {
+    // When contentOffset={{x:0,y:0}} with lazy load items, setContentOffset
+    // is repeatedly called, causing an unexpected scroll to top behavior.
+    // Avoid updating contentOffset if the value has not changed.
+    if (mCurrentContentOffset == null || !mCurrentContentOffset.equals(value)) {
+      mCurrentContentOffset = value;
+
+      if (value != null) {
+        double x = value.hasKey("x") ? value.getDouble("x") : 0;
+        double y = value.hasKey("y") ? value.getDouble("y") : 0;
+        scrollTo((int) PixelUtil.toPixelFromDIP(x), (int) PixelUtil.toPixelFromDIP(y));
+      } else {
+        scrollTo(0, 0);
+      }
+    }
+  }
+
   /**
    * Calls `smoothScrollTo` and updates state.
    *

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewManager.java

@@ -320,13 +320,7 @@ public void setFadingEdgeLength(ReactScrollView view, int value) {
 
   @ReactProp(name = "contentOffset", customType = "Point")
   public void setContentOffset(ReactScrollView view, ReadableMap value) {
-    if (value != null) {
-      double x = value.hasKey("x") ? value.getDouble("x") : 0;
-      double y = value.hasKey("y") ? value.getDouble("y") : 0;
-      view.scrollTo((int) PixelUtil.toPixelFromDIP(x), (int) PixelUtil.toPixelFromDIP(y));
-    } else {
-      view.scrollTo(0, 0);
-    }
+    view.setContentOffset(value);
   }
 
   @Override