Refactor predictFinalScrollPosition method to the helper class

Summary:
This diff refactors method `predictFinalScrollPosition` in `ReactScrollView` and `ReactHorizontalScrollView` to the helper class. This will make future changes to the prediction logic easier.

Changelog:
[Internal]

Reviewed By: javache

Differential Revision: D32571735

fbshipit-source-id: 7e7e21ac51f929a017cd43de094ed39478fe4032

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

@@ -93,7 +93,6 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
   private int mEndFillColor = Color.TRANSPARENT;
   private boolean mDisableIntervalMomentum = false;
   private int mSnapInterval = 0;
-  private float mDecelerationRate = 0.985f;
   private @Nullable List<Integer> mSnapOffsets;
   private boolean mSnapToStart = true;
   private boolean mSnapToEnd = true;
@@ -216,10 +215,10 @@ public void setPagingEnabled(boolean pagingEnabled) {
   }
 
   public void setDecelerationRate(float decelerationRate) {
-    mDecelerationRate = decelerationRate;
+    getReactScrollViewScrollState().setDecelerationRate(decelerationRate);
 
     if (mScroller != null) {
-      mScroller.setFriction(1.0f - mDecelerationRate);
+      mScroller.setFriction(1.0f - decelerationRate);
     }
   }
 
@@ -802,32 +801,9 @@ public void run() {
   }
 
   private int predictFinalScrollPosition(int velocityX) {
-    // ScrollView can *only* scroll for 250ms when using smoothScrollTo and there's
-    // no way to customize the scroll duration. So, we create a temporary OverScroller
-    // so we can predict where a fling would land and snap to nearby that point.
-    OverScroller scroller = new OverScroller(getContext());
-    scroller.setFriction(1.0f - mDecelerationRate);
-
     // predict where a fling would end up so we can scroll to the nearest snap offset
-    int maximumOffset = Math.max(0, computeHorizontalScrollRange() - getWidth());
-    int width = getWidth() - ViewCompat.getPaddingStart(this) - ViewCompat.getPaddingEnd(this);
-    scroller.fling(
-        ReactScrollViewHelper.getNextFlingStartValue(
-            this,
-            getScrollX(),
-            getReactScrollViewScrollState().getFinalAnimatedPositionScroll().x,
-            velocityX), // startX
-        getScrollY(), // startY
-        velocityX, // velocityX
-        0, // velocityY
-        0, // minX
-        maximumOffset, // maxX
-        0, // minY
-        0, // maxY
-        width / 2, // overX
-        0 // overY
-        );
-    return scroller.getFinalX();
+    final int maximumOffset = Math.max(0, computeHorizontalScrollRange() - getWidth());
+    return ReactScrollViewHelper.predictFinalScrollPosition(this, velocityX, 0, maximumOffset, 0).x;
   }
 
   /**

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

@@ -89,7 +89,6 @@ public class ReactScrollView extends ScrollView
   private int mEndFillColor = Color.TRANSPARENT;
   private boolean mDisableIntervalMomentum = false;
   private int mSnapInterval = 0;
-  private float mDecelerationRate = 0.985f;
   private @Nullable List<Integer> mSnapOffsets;
   private boolean mSnapToStart = true;
   private boolean mSnapToEnd = true;
@@ -191,10 +190,10 @@ public void setPagingEnabled(boolean pagingEnabled) {
   }
 
   public void setDecelerationRate(float decelerationRate) {
-    mDecelerationRate = decelerationRate;
+    getReactScrollViewScrollState().setDecelerationRate(decelerationRate);
 
     if (mScroller != null) {
-      mScroller.setFriction(1.0f - mDecelerationRate);
+      mScroller.setFriction(1.0f - decelerationRate);
     }
   }
 
@@ -591,32 +590,9 @@ public void run() {
   }
 
   private int predictFinalScrollPosition(int velocityY) {
-    // ScrollView can *only* scroll for 250ms when using smoothScrollTo and there's
-    // no way to customize the scroll duration. So, we create a temporary OverScroller
-    // so we can predict where a fling would land and snap to nearby that point.
-    OverScroller scroller = new OverScroller(getContext());
-    scroller.setFriction(1.0f - mDecelerationRate);
-
     // predict where a fling would end up so we can scroll to the nearest snap offset
-    int maximumOffset = getMaxScrollY();
-    int height = getHeight() - getPaddingBottom() - getPaddingTop();
-    scroller.fling(
-        getScrollX(), // startX
-        ReactScrollViewHelper.getNextFlingStartValue(
-            this,
-            getScrollY(),
-            getReactScrollViewScrollState().getFinalAnimatedPositionScroll().y,
-            velocityY), // startY
-        0, // velocityX
-        velocityY, // velocityY
-        0, // minX
-        0, // maxX
-        0, // minY
-        maximumOffset, // maxY
-        0, // overX
-        height / 2 // overY
-        );
-    return scroller.getFinalY();
+    return ReactScrollViewHelper.predictFinalScrollPosition(this, 0, velocityY, 0, getMaxScrollY())
+        .y;
   }
 
   private View getContentView() {

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

@@ -15,6 +15,7 @@
 import android.view.ViewGroup;
 import android.widget.OverScroller;
 import androidx.annotation.Nullable;
+import androidx.core.view.ViewCompat;
 import com.facebook.common.logging.FLog;
 import com.facebook.react.bridge.JSApplicationIllegalArgumentException;
 import com.facebook.react.bridge.ReactContext;
@@ -222,6 +223,7 @@ public static class ReactScrollViewScrollState {
     private final Point mLastStateUpdateScroll = new Point(-1, -1);
     private boolean mIsCanceled = false;
     private boolean mIsFinished = true;
+    private float mDecelerationRate = 0.985f;
 
     public ReactScrollViewScrollState(final int layoutDirection) {
       mLayoutDirection = layoutDirection;
@@ -291,6 +293,17 @@ public ReactScrollViewScrollState setIsFinished(boolean isFinished) {
       mIsFinished = isFinished;
       return this;
     }
+
+    /** Get true if previous animation was finished */
+    public float getDecelerationRate() {
+      return mDecelerationRate;
+    }
+
+    /** Set the state of current animation is finished or not */
+    public ReactScrollViewScrollState setDecelerationRate(float decelerationRate) {
+      mDecelerationRate = decelerationRate;
+      return this;
+    }
   }
 
   /**
@@ -491,6 +504,54 @@ public void onAnimationRepeat(Animator animator) {}
             });
   }
 
+  public static <
+          T extends
+              ViewGroup & FabricViewStateManager.HasFabricViewStateManager & HasScrollState
+                  & HasFlingAnimator>
+      Point predictFinalScrollPosition(
+          final T scrollView,
+          int velocityX,
+          int velocityY,
+          int maximumOffsetX,
+          int maximumOffsetY) {
+    final ReactScrollViewScrollState scrollState = scrollView.getReactScrollViewScrollState();
+    // ScrollView can *only* scroll for 250ms when using smoothScrollTo and there's
+    // no way to customize the scroll duration. So, we create a temporary OverScroller
+    // so we can predict where a fling would land and snap to nearby that point.
+    OverScroller scroller = new OverScroller(scrollView.getContext());
+    scroller.setFriction(1.0f - scrollState.getDecelerationRate());
+
+    // predict where a fling would end up so we can scroll to the nearest snap offset
+    int width =
+        scrollView.getWidth()
+            - ViewCompat.getPaddingStart(scrollView)
+            - ViewCompat.getPaddingEnd(scrollView);
+    int height =
+        scrollView.getHeight() - scrollView.getPaddingBottom() - scrollView.getPaddingTop();
+    Point finalAnimatedPositionScroll = scrollState.getFinalAnimatedPositionScroll();
+    scroller.fling(
+        getNextFlingStartValue(
+            scrollView,
+            scrollView.getScrollX(),
+            finalAnimatedPositionScroll.x,
+            velocityX), // startX
+        getNextFlingStartValue(
+            scrollView,
+            scrollView.getScrollY(),
+            finalAnimatedPositionScroll.y,
+            velocityY), // startY
+        velocityX, // velocityX
+        velocityY, // velocityY
+        0, // minX
+        maximumOffsetX, // maxX
+        0, // minY
+        maximumOffsetY, // maxY
+        width / 2, // overX
+        height / 2 // overY
+        );
+    return new Point(scroller.getFinalX(), scroller.getFinalY());
+  }
+
   public interface HasScrollState {
     /** Get the scroll state for the current ScrollView */
     ReactScrollViewScrollState getReactScrollViewScrollState();