Add snapToAlignment to ReactHorizontalScrollViewManager

Summary:
This diff adds the new snapToAlignment into ReactHorizontalScrollViewManager

changelog: [Android][Added] Implement snapToAlignment into ReactHorizontalScrollViewManager

Reviewed By: JoshuaGross

Differential Revision: D31174545

fbshipit-source-id: c56bfca207980428be98dd21a5387a0ff6bcd296

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

@@ -7,6 +7,8 @@
 
 package com.facebook.react.views.scroll;
 
+import static com.facebook.react.views.scroll.ReactScrollViewHelper.SNAP_ALIGNMENT_DISABLED;
+
 import android.animation.Animator;
 import android.animation.ObjectAnimator;
 import android.animation.PropertyValuesHolder;
@@ -94,6 +96,7 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
   private @Nullable List<Integer> mSnapOffsets;
   private boolean mSnapToStart = true;
   private boolean mSnapToEnd = true;
+  private int mSnapToAlignment = SNAP_ALIGNMENT_DISABLED;
   private ReactViewBackgroundManager mReactBackgroundManager;
   private boolean mPagedArrowScrolling = false;
   private int pendingContentOffsetX = UNSET_CONTENT_OFFSET;
@@ -239,6 +242,10 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
     mSnapToEnd = snapToEnd;
   }
 
+  public void setSnapToAlignment(int snapToAlignment) {
+    mSnapToAlignment = snapToAlignment;
+  }
+
   public void flashScrollIndicators() {
     awakenScrollBars();
   }

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

@@ -102,6 +102,11 @@ public class ReactHorizontalScrollViewManager extends ViewGroupManager<ReactHori
     view.setSnapInterval((int) (snapToInterval * screenDisplayMetrics.density));
   }
 
+  @ReactProp(name = "snapToAlignment")
+  public void setSnapToAlignment(ReactHorizontalScrollView view, String alignment) {
+    view.setSnapToAlignment(ReactScrollViewHelper.parseSnapToAlignment(alignment));
+  }
+
   @ReactProp(name = "snapToOffsets")
   public void setSnapToOffsets(
       ReactHorizontalScrollView view, @Nullable ReadableArray snapToOffsets) {

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

@@ -11,6 +11,7 @@ import android.content.Context;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.OverScroller;
+import androidx.annotation.Nullable;
 import com.facebook.react.bridge.JSApplicationIllegalArgumentException;
 import com.facebook.react.bridge.ReactContext;
 import com.facebook.react.uimanager.UIManagerHelper;
@@ -26,6 +27,11 @@ public class ReactScrollViewHelper {
   public static final String AUTO = "auto";
   public static final String OVER_SCROLL_NEVER = "never";
 
+  public static final int SNAP_ALIGNMENT_DISABLED = 0;
+  public static final int SNAP_ALIGNMENT_START = 1;
+  public static final int SNAP_ALIGNMENT_CENTER = 2;
+  public static final int SNAP_ALIGNMENT_END = 3;
+
   public interface ScrollListener {
     void onScroll(
         ViewGroup scrollView, ScrollEventType scrollEventType, float xVelocity, float yVelocity);
@@ -119,6 +125,20 @@ public class ReactScrollViewHelper {
     }
   }
 
+  public static int parseSnapToAlignment(@Nullable String alignment) {
+    if (alignment == null) {
+      return SNAP_ALIGNMENT_DISABLED;
+    } else if ("start".equalsIgnoreCase(alignment)) {
+      return SNAP_ALIGNMENT_START;
+    } else if ("center".equalsIgnoreCase(alignment)) {
+      return SNAP_ALIGNMENT_CENTER;
+    } else if ("end".equals(alignment)) {
+      return SNAP_ALIGNMENT_END;
+    } else {
+      throw new JSApplicationIllegalArgumentException("wrong snap alignment value: " + alignment);
+    }
+  }
+
   public static int getDefaultScrollAnimationDuration(Context context) {
     if (!mSmoothScrollDurationInitialized) {
       mSmoothScrollDurationInitialized = true;