Support contentOffset property in Android's ScrollView and HorizontalScrollView

Summary:
For a very long time, iOS has supported the `contentOffset` property but Android has not:

#6849

This property can be used, primarily, to autoscroll the ScrollView to a starting position when it is first rendered, to avoid "jumps" that occur by asynchronously scrolling to a start position.

Changelog: [Android][Changed] ScrollView now supports `contentOffset`

Reviewed By: mdvacca

Differential Revision: D21198236

fbshipit-source-id: 2b0773569ba42120cb1fcf0f3847ca98af2285e7

Author: JoshuaGross

Libraries/Components/ScrollView/AndroidHorizontalScrollViewNativeComponent.js

@@ -37,6 +37,7 @@ const AndroidHorizontalScrollViewViewConfig = {
     snapToInterval: true,
     snapToStart: true,
     snapToOffsets: true,
+    contentOffset: true,
   },
 };
 

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

@@ -50,6 +50,8 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
   private static final String CONTENT_OFFSET_LEFT = "contentOffsetLeft";
   private static final String CONTENT_OFFSET_TOP = "contentOffsetTop";
 
+  private static final int UNSET_CONTENT_OFFSET = -1;
+
   private final OnScrollDispatchHelper mOnScrollDispatchHelper = new OnScrollDispatchHelper();
   private final @Nullable OverScroller mScroller;
   private final VelocityHelper mVelocityHelper = new VelocityHelper();
@@ -76,6 +78,8 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
   private boolean mSnapToEnd = true;
   private ReactViewBackgroundManager mReactBackgroundManager;
   private boolean mPagedArrowScrolling = false;
+  private int pendingContentOffsetX = UNSET_CONTENT_OFFSET;
+  private int pendingContentOffsetY = UNSET_CONTENT_OFFSET;
   private @Nullable StateWrapper mStateWrapper;
 
   private final Rect mTempRect = new Rect();
@@ -224,7 +228,13 @@ protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
   @Override
   protected void onLayout(boolean changed, int l, int t, int r, int b) {
     // Call with the present values in order to re-layout if necessary
-    reactScrollTo(getScrollX(), getScrollY());
+    // If a "pending" value has been set, we restore that value.
+    // That value gets cleared by reactScrollTo.
+    int scrollToX =
+        pendingContentOffsetX != UNSET_CONTENT_OFFSET ? pendingContentOffsetX : getScrollX();
+    int scrollToY =
+        pendingContentOffsetY != UNSET_CONTENT_OFFSET ? pendingContentOffsetY : getScrollY();
+    reactScrollTo(scrollToX, scrollToY);
   }
 
   /**
@@ -906,6 +916,7 @@ public void setBorderStyle(@Nullable String style) {
   public void reactSmoothScrollTo(int x, int y) {
     smoothScrollTo(x, y);
     updateStateOnScroll(x, y);
+    setPendingContentOffsets(x, y);
   }
 
   /**
@@ -917,6 +928,25 @@ public void reactSmoothScrollTo(int x, int y) {
   public void reactScrollTo(int x, int y) {
     scrollTo(x, y);
     updateStateOnScroll(x, y);
+    setPendingContentOffsets(x, y);
+  }
+
+  /**
+   * If contentOffset is set before the View has been laid out, store the values and set them when
+   * `onLayout` is called.
+   *
+   * @param x
+   * @param y
+   */
+  private void setPendingContentOffsets(int x, int y) {
+    View child = getChildAt(0);
+    if (child != null && child.getWidth() != 0 && child.getHeight() != 0) {
+      pendingContentOffsetX = UNSET_CONTENT_OFFSET;
+      pendingContentOffsetY = UNSET_CONTENT_OFFSET;
+    } else {
+      pendingContentOffsetX = x;
+      pendingContentOffsetY = y;
+    }
   }
 
   public void updateState(@Nullable StateWrapper stateWrapper) {

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

@@ -12,6 +12,7 @@
 import androidx.annotation.Nullable;
 import androidx.core.view.ViewCompat;
 import com.facebook.react.bridge.ReadableArray;
+import com.facebook.react.bridge.ReadableMap;
 import com.facebook.react.module.annotations.ReactModule;
 import com.facebook.react.uimanager.DisplayMetricsHolder;
 import com.facebook.react.uimanager.PixelUtil;
@@ -299,4 +300,11 @@ public void setFadingEdgeLength(ReactHorizontalScrollView view, int value) {
       view.setFadingEdgeLength(0);
     }
   }
+
+  @ReactProp(name = "contentOffset")
+  public void setContentOffset(ReactHorizontalScrollView view, ReadableMap value) {
+    double x = value.getDouble("x");
+    double y = value.getDouble("y");
+    view.reactScrollTo((int) PixelUtil.toPixelFromDIP(x), (int) PixelUtil.toPixelFromDIP(y));
+  }
 }

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

@@ -55,6 +55,8 @@ public class ReactScrollView extends ScrollView
   private static final String CONTENT_OFFSET_LEFT = "contentOffsetLeft";
   private static final String CONTENT_OFFSET_TOP = "contentOffsetTop";
 
+  private static final int UNSET_CONTENT_OFFSET = -1;
+
   private final OnScrollDispatchHelper mOnScrollDispatchHelper = new OnScrollDispatchHelper();
   private final @Nullable OverScroller mScroller;
   private final VelocityHelper mVelocityHelper = new VelocityHelper();
@@ -81,6 +83,8 @@ public class ReactScrollView extends ScrollView
   private boolean mSnapToEnd = true;
   private View mContentView;
   private ReactViewBackgroundManager mReactBackgroundManager;
+  private int pendingContentOffsetX = UNSET_CONTENT_OFFSET;
+  private int pendingContentOffsetY = UNSET_CONTENT_OFFSET;
   private @Nullable StateWrapper mStateWrapper;
 
   public ReactScrollView(ReactContext context) {
@@ -200,7 +204,13 @@ protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
   @Override
   protected void onLayout(boolean changed, int l, int t, int r, int b) {
     // Call with the present values in order to re-layout if necessary
-    reactScrollTo(getScrollX(), getScrollY());
+    // If a "pending" value has been set, we restore that value.
+    // That value gets cleared by reactScrollTo.
+    int scrollToX =
+        pendingContentOffsetX != UNSET_CONTENT_OFFSET ? pendingContentOffsetX : getScrollX();
+    int scrollToY =
+        pendingContentOffsetY != UNSET_CONTENT_OFFSET ? pendingContentOffsetY : getScrollY();
+    reactScrollTo(scrollToX, scrollToY);
   }
 
   @Override
@@ -777,6 +787,7 @@ public void onChildViewRemoved(View parent, View child) {
   public void reactSmoothScrollTo(int x, int y) {
     smoothScrollTo(x, y);
     updateStateOnScroll(x, y);
+    setPendingContentOffsets(x, y);
   }
 
   /**
@@ -788,6 +799,25 @@ public void reactSmoothScrollTo(int x, int y) {
   public void reactScrollTo(int x, int y) {
     scrollTo(x, y);
     updateStateOnScroll(x, y);
+    setPendingContentOffsets(x, y);
+  }
+
+  /**
+   * If contentOffset is set before the View has been laid out, store the values and set them when
+   * `onLayout` is called.
+   *
+   * @param x
+   * @param y
+   */
+  private void setPendingContentOffsets(int x, int y) {
+    View child = getChildAt(0);
+    if (child != null && child.getWidth() != 0 && child.getHeight() != 0) {
+      pendingContentOffsetX = UNSET_CONTENT_OFFSET;
+      pendingContentOffsetY = UNSET_CONTENT_OFFSET;
+    } else {
+      pendingContentOffsetX = x;
+      pendingContentOffsetY = y;
+    }
   }
 
   /**