Tweaking fast scroller to follow touch closer.

- Issue: The fast scroller currently does not follow the touch input
  because fundamentally, the fixed scrollbar height and the mapping
  of the scroll space to the scrollbar space is fundamentally incompatible.
- This CL changes the fast scroller to allow it to detach when the user
  fast-scrolls, then re-attaches after the user scrolls the screen and
  the current scroll position for the scrollbar picks up the thumb position.
- Since the scroll position and the fast scroller thumb is now detached,
  we can change the distribution of the fast scroll letters to make it
  independent of the rows for each section and instead uniformly distribute
  it along the scrollbar, which allows for more stability.
- There are edge cases where this fails, especially when there are few
  apps, which we can investigate further.
  
Bug: 20035978

Change-Id: I8322f862107e6f330deff692885233706564bffd

7 files changed, 162 insertions, 62 deletions

diff --git a/proguard.flags b/proguard.flags
index a8e2b6092..b4365fee4 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -3,8 +3,8 @@
 }
 
 -keep class com.android.launcher3.BaseRecyclerViewFastScrollBar {
-  public void setWidth(int);
-  public int getWidth();
+  public void setThumbWidth(int);
+  public int getThumbWidth();
   public void setTrackAlpha(int);
   public int getTrackAlpha();
 }
diff --git a/src/com/android/launcher3/BaseRecyclerView.java b/src/com/android/launcher3/BaseRecyclerView.java
index 0fae427e8..f0d8b3b3d 100644
--- a/src/com/android/launcher3/BaseRecyclerView.java
+++ b/src/com/android/launcher3/BaseRecyclerView.java
@@ -92,9 +92,15 @@ public abstract class BaseRecyclerView extends RecyclerView
             // TODO(winsonc): If we want to animate the section heads while scrolling, we can
             //                initiate that here if the recycler view scroll state is not
             //                RecyclerView.SCROLL_STATE_IDLE.
+
+            onUpdateScrollbar(dy);
         }
     }
 
+    public void reset() {
+        mScrollbar.reattachThumbToScroll();
+    }
+
     @Override
     protected void onFinishInflate() {
         super.onFinishInflate();
@@ -143,7 +149,7 @@ public abstract class BaseRecyclerView extends RecyclerView
                 mScrollbar.handleTouchEvent(ev, mDownX, mDownY, mLastY);
                 break;
         }
-        return mScrollbar.isDragging();
+        return mScrollbar.isDraggingThumb();
     }
 
     public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
@@ -185,12 +191,10 @@ public abstract class BaseRecyclerView extends RecyclerView
      *   AvailableScrollHeight = Total height of the all items - last page height
      *
      * This assumes that all rows are the same height.
-     *
-     * @param yOffset the offset from the top of the recycler view to start tracking.
      */
-    protected int getAvailableScrollHeight(int rowCount, int rowHeight, int yOffset) {
+    protected int getAvailableScrollHeight(int rowCount, int rowHeight) {
         int visibleHeight = getHeight() - mBackgroundPadding.top - mBackgroundPadding.bottom;
-        int scrollHeight = getPaddingTop() + yOffset + rowCount * rowHeight + getPaddingBottom();
+        int scrollHeight = getPaddingTop() + rowCount * rowHeight + getPaddingBottom();
         int availableScrollHeight = scrollHeight - visibleHeight;
         return availableScrollHeight;
     }
@@ -222,7 +226,7 @@ public abstract class BaseRecyclerView extends RecyclerView
     @Override
     protected void dispatchDraw(Canvas canvas) {
         super.dispatchDraw(canvas);
-        onUpdateScrollbar();
+        onUpdateScrollbar(0);
         mScrollbar.draw(canvas);
     }
 
@@ -234,24 +238,21 @@ public abstract class BaseRecyclerView extends RecyclerView
      * @param scrollPosState the current scroll position
      * @param rowCount the number of rows, used to calculate the total scroll height (assumes that
      *                 all rows are the same height)
-     * @param yOffset the offset to start tracking in the recycler view (only used for all apps)
      */
     protected void synchronizeScrollBarThumbOffsetToViewScroll(ScrollPositionState scrollPosState,
-            int rowCount, int yOffset) {
-        int availableScrollHeight = getAvailableScrollHeight(rowCount, scrollPosState.rowHeight,
-                yOffset);
-        int availableScrollBarHeight = getAvailableScrollBarHeight();
-
+            int rowCount) {
         // Only show the scrollbar if there is height to be scrolled
+        int availableScrollBarHeight = getAvailableScrollBarHeight();
+        int availableScrollHeight = getAvailableScrollHeight(rowCount, scrollPosState.rowHeight);
         if (availableScrollHeight <= 0) {
-            mScrollbar.setScrollbarThumbOffset(-1, -1);
+            mScrollbar.setThumbOffset(-1, -1);
             return;
         }
 
         // Calculate the current scroll position, the scrollY of the recycler view accounts for the
         // view padding, while the scrollBarY is drawn right up to the background padding (ignoring
         // padding)
-        int scrollY = getPaddingTop() + yOffset +
+        int scrollY = getPaddingTop() +
                 (scrollPosState.rowIndex * scrollPosState.rowHeight) - scrollPosState.rowTopOffset;
         int scrollBarY = mBackgroundPadding.top +
                 (int) (((float) scrollY / availableScrollHeight) * availableScrollBarHeight);
@@ -261,9 +262,9 @@ public abstract class BaseRecyclerView extends RecyclerView
         if (Utilities.isRtl(getResources())) {
             scrollBarX = mBackgroundPadding.left;
         } else {
-            scrollBarX = getWidth() - mBackgroundPadding.right - mScrollbar.getWidth();
+            scrollBarX = getWidth() - mBackgroundPadding.right - mScrollbar.getThumbWidth();
         }
-        mScrollbar.setScrollbarThumbOffset(scrollBarX, scrollBarY);
+        mScrollbar.setThumbOffset(scrollBarX, scrollBarY);
     }
 
     /**
@@ -276,10 +277,15 @@ public abstract class BaseRecyclerView extends RecyclerView
      * Updates the bounds for the scrollbar.
      * <p>Override in each subclass of this base class.
      */
-    public abstract void onUpdateScrollbar();
+    public abstract void onUpdateScrollbar(int dy);
 
     /**
      * <p>Override in each subclass of this base class.
      */
     public void onFastScrollCompleted() {}
+
+    /**
+     * Returns information about the item that the recycler view is currently scrolled to.
+     */
+    protected abstract void getCurScrollState(ScrollPositionState stateOut);
 }
\ No newline at end of file
diff --git a/src/com/android/launcher3/BaseRecyclerViewFastScrollBar.java b/src/com/android/launcher3/BaseRecyclerViewFastScrollBar.java
index 2c4184dc4..29e234d6c 100644
--- a/src/com/android/launcher3/BaseRecyclerViewFastScrollBar.java
+++ b/src/com/android/launcher3/BaseRecyclerViewFastScrollBar.java
@@ -56,9 +56,12 @@ public class BaseRecyclerViewFastScrollBar {
     private int mThumbMaxWidth;
     @Thunk int mThumbWidth;
     @Thunk int mThumbHeight;
+    private float mLastTouchY;
     // The inset is the buffer around which a point will still register as a click on the scrollbar
     private int mTouchInset;
     private boolean mIsDragging;
+    private boolean mIsThumbDetached;
+    private boolean mCanThumbDetach;
 
     // This is the offset from the top of the scrollbar when the user first starts touching.  To
     // prevent jumping, this offset is applied as the user scrolls.
@@ -84,7 +87,15 @@ public class BaseRecyclerViewFastScrollBar {
         mTouchInset = res.getDimensionPixelSize(R.dimen.container_fastscroll_thumb_touch_inset);
     }
 
-    public void setScrollbarThumbOffset(int x, int y) {
+    public void setDetachThumbOnFastScroll() {
+        mCanThumbDetach = true;
+    }
+
+    public void reattachThumbToScroll() {
+        mIsThumbDetached = false;
+    }
+
+    public void setThumbOffset(int x, int y) {
         if (mThumbOffset.x == x && mThumbOffset.y == y) {
             return;
         }
@@ -95,8 +106,12 @@ public class BaseRecyclerViewFastScrollBar {
         mRv.invalidate(mInvalidateRect);
     }
 
+    public Point getThumbOffset() {
+        return mThumbOffset;
+    }
+
     // Setter/getter for the search bar width for animations
-    public void setWidth(int width) {
+    public void setThumbWidth(int width) {
         mInvalidateRect.set(mThumbOffset.x, 0, mThumbOffset.x + mThumbWidth, mRv.getHeight());
         mThumbWidth = width;
         mInvalidateRect.union(new Rect(mThumbOffset.x, 0, mThumbOffset.x + mThumbWidth,
@@ -104,7 +119,7 @@ public class BaseRecyclerViewFastScrollBar {
         mRv.invalidate(mInvalidateRect);
     }
 
-    public int getWidth() {
+    public int getThumbWidth() {
         return mThumbWidth;
     }
 
@@ -127,10 +142,18 @@ public class BaseRecyclerViewFastScrollBar {
         return mThumbMaxWidth;
     }
 
-    public boolean isDragging() {
+    public float getLastTouchY() {
+        return mLastTouchY;
+    }
+
+    public boolean isDraggingThumb() {
         return mIsDragging;
     }
 
+    public boolean isThumbDetached() {
+        return mIsThumbDetached;
+    }
+
     /**
      * Handles the touch event and determines whether to show the fast scroller (or updates it if
      * it is already showing).
@@ -152,6 +175,9 @@ public class BaseRecyclerViewFastScrollBar {
                         Math.abs(y - downY) > config.getScaledTouchSlop()) {
                     mRv.getParent().requestDisallowInterceptTouchEvent(true);
                     mIsDragging = true;
+                    if (mCanThumbDetach) {
+                        mIsThumbDetached = true;
+                    }
                     mTouchOffset += (lastY - downY);
                     mPopup.animateVisibility(true);
                     animateScrollbar(true);
@@ -166,11 +192,13 @@ public class BaseRecyclerViewFastScrollBar {
                     mPopup.setSectionName(sectionName);
                     mPopup.animateVisibility(!sectionName.isEmpty());
                     mRv.invalidate(mPopup.updateFastScrollerBounds(mRv, lastY));
+                    mLastTouchY = boundedY;
                 }
                 break;
             case MotionEvent.ACTION_UP:
             case MotionEvent.ACTION_CANCEL:
                 mTouchOffset = 0;
+                mLastTouchY = 0;
                 if (mIsDragging) {
                     mIsDragging = false;
                     mPopup.animateVisibility(false);
@@ -205,7 +233,7 @@ public class BaseRecyclerViewFastScrollBar {
         }
         ObjectAnimator trackAlphaAnim = ObjectAnimator.ofInt(this, "trackAlpha",
                 isScrolling ? MAX_TRACK_ALPHA : 0);
-        ObjectAnimator thumbWidthAnim = ObjectAnimator.ofInt(this, "width",
+        ObjectAnimator thumbWidthAnim = ObjectAnimator.ofInt(this, "thumbWidth",
                 isScrolling ? mThumbMaxWidth : mThumbMinWidth);
         ValueAnimator colorAnimation = ValueAnimator.ofObject(new ArgbEvaluator(),
                 mThumbPaint.getColor(), isScrolling ? mThumbActiveColor : mThumbInactiveColor);
diff --git a/src/com/android/launcher3/allapps/AllAppsContainerView.java b/src/com/android/launcher3/allapps/AllAppsContainerView.java
index e129dc6d3..6d008ab98 100644
--- a/src/com/android/launcher3/allapps/AllAppsContainerView.java
+++ b/src/com/android/launcher3/allapps/AllAppsContainerView.java
@@ -555,8 +555,9 @@ public class AllAppsContainerView extends BaseContainerView implements DragSourc
     @Override
     public void onLauncherTransitionEnd(Launcher l, boolean animated, boolean toWorkspace) {
         if (toWorkspace) {
-            // Reset the search bar after transitioning home
+            // Reset the search bar and base recycler view after transitioning home
             mSearchBarController.reset();
+            mAppsRecyclerView.reset();
         }
     }
 
diff --git a/src/com/android/launcher3/allapps/AllAppsRecyclerView.java b/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
index 5aa973a15..5ec8bb258 100644
--- a/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
+++ b/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
@@ -72,6 +72,7 @@ public class AllAppsRecyclerView extends BaseRecyclerView
     public AllAppsRecyclerView(Context context, AttributeSet attrs, int defStyleAttr,
             int defStyleRes) {
         super(context, attrs, defStyleAttr);
+        mScrollbar.setDetachThumbOnFastScroll();
     }
 
     /**
@@ -168,8 +169,8 @@ public class AllAppsRecyclerView extends BaseRecyclerView
         }
 
         // Map the touch position back to the scroll of the recycler view
-        getCurScrollState(mScrollPosState, mApps.getAdapterItems());
-        int availableScrollHeight = getAvailableScrollHeight(rowCount, mScrollPosState.rowHeight, 0);
+        getCurScrollState(mScrollPosState);
+        int availableScrollHeight = getAvailableScrollHeight(rowCount, mScrollPosState.rowHeight);
         LinearLayoutManager layoutManager = (LinearLayoutManager) getLayoutManager();
         if (mFastScrollMode == FAST_SCROLL_MODE_FREE_SCROLL) {
             layoutManager.scrollToPositionWithOffset(0, (int) -(availableScrollHeight * touchFraction));
@@ -216,24 +217,73 @@ public class AllAppsRecyclerView extends BaseRecyclerView
      * Updates the bounds for the scrollbar.
      */
     @Override
-    public void onUpdateScrollbar() {
+    public void onUpdateScrollbar(int dy) {
         List<AlphabeticalAppsList.AdapterItem> items = mApps.getAdapterItems();
 
         // Skip early if there are no items or we haven't been measured
         if (items.isEmpty() || mNumAppsPerRow == 0) {
-            mScrollbar.setScrollbarThumbOffset(-1, -1);
+            mScrollbar.setThumbOffset(-1, -1);
             return;
         }
 
         // Find the index and height of the first visible row (all rows have the same height)
         int rowCount = mApps.getNumAppRows();
-        getCurScrollState(mScrollPosState, items);
+        getCurScrollState(mScrollPosState);
         if (mScrollPosState.rowIndex < 0) {
-            mScrollbar.setScrollbarThumbOffset(-1, -1);
+            mScrollbar.setThumbOffset(-1, -1);
             return;
         }
 
-        synchronizeScrollBarThumbOffsetToViewScroll(mScrollPosState, rowCount, 0);
+        // Only show the scrollbar if there is height to be scrolled
+        int availableScrollBarHeight = getAvailableScrollBarHeight();
+        int availableScrollHeight = getAvailableScrollHeight(mApps.getNumAppRows(), mScrollPosState.rowHeight);
+        if (availableScrollHeight <= 0) {
+            mScrollbar.setThumbOffset(-1, -1);
+            return;
+        }
+
+        // Calculate the current scroll position, the scrollY of the recycler view accounts for the
+        // view padding, while the scrollBarY is drawn right up to the background padding (ignoring
+        // padding)
+        int scrollY = getPaddingTop() +
+                (mScrollPosState.rowIndex * mScrollPosState.rowHeight) - mScrollPosState.rowTopOffset;
+        int scrollBarY = mBackgroundPadding.top +
+                (int) (((float) scrollY / availableScrollHeight) * availableScrollBarHeight);
+
+        if (mScrollbar.isThumbDetached()) {
+            int scrollBarX;
+            if (Utilities.isRtl(getResources())) {
+                scrollBarX = mBackgroundPadding.left;
+            } else {
+                scrollBarX = getWidth() - mBackgroundPadding.right - mScrollbar.getThumbWidth();
+            }
+
+            if (mScrollbar.isDraggingThumb()) {
+                // If the thumb is detached, then just update the thumb to the current
+                // touch position
+                mScrollbar.setThumbOffset(scrollBarX, (int) mScrollbar.getLastTouchY());
+            } else {
+                int thumbScrollY = mScrollbar.getThumbOffset().y;
+                int diffScrollY = scrollBarY - thumbScrollY;
+                if (diffScrollY * dy > 0f) {
+                    // User is scrolling in the same direction the thumb needs to catch up to the
+                    // current scroll position.
+                    thumbScrollY += dy < 0 ? Math.max(dy, diffScrollY) : Math.min(dy, diffScrollY);
+                    thumbScrollY = Math.max(0, Math.min(availableScrollBarHeight, thumbScrollY));
+                    mScrollbar.setThumbOffset(scrollBarX, thumbScrollY);
+                    if (scrollBarY == thumbScrollY) {
+                        mScrollbar.reattachThumbToScroll();
+                    }
+                } else {
+                    // User is scrolling in an opposite direction to the direction that the thumb
+                    // needs to catch up to the scroll position.  Do nothing except for updating
+                    // the scroll bar x to match the thumb width.
+                    mScrollbar.setThumbOffset(scrollBarX, thumbScrollY);
+                }
+            }
+        } else {
+            synchronizeScrollBarThumbOffsetToViewScroll(mScrollPosState, rowCount);
+        }
     }
 
     /**
@@ -285,13 +335,13 @@ public class AllAppsRecyclerView extends BaseRecyclerView
     /**
      * Returns the current scroll state of the apps rows.
      */
-    private void getCurScrollState(ScrollPositionState stateOut,
-            List<AlphabeticalAppsList.AdapterItem> items) {
+    protected void getCurScrollState(ScrollPositionState stateOut) {
         stateOut.rowIndex = -1;
         stateOut.rowTopOffset = -1;
         stateOut.rowHeight = -1;
 
         // Return early if there are no items or we haven't been measured
+        List<AlphabeticalAppsList.AdapterItem> items = mApps.getAdapterItems();
         if (items.isEmpty() || mNumAppsPerRow == 0) {
             return;
         }
diff --git a/src/com/android/launcher3/allapps/AlphabeticalAppsList.java b/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
index 396f75790..dac0df12a 100644
--- a/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
+++ b/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
@@ -43,6 +43,11 @@ public class AlphabeticalAppsList {
     private static final boolean DEBUG = false;
     private static final boolean DEBUG_PREDICTIONS = false;
 
+    private static final int FAST_SCROLL_FRACTION_DISTRIBUTE_BY_ROWS_FRACTION = 0;
+    private static final int FAST_SCROLL_FRACTION_DISTRIBUTE_BY_NUM_SECTIONS = 1;
+
+    private final int mFastScrollDistributionMode = FAST_SCROLL_FRACTION_DISTRIBUTE_BY_NUM_SECTIONS;
+
     /**
      * Info about a section in the alphabetic list
      */
@@ -85,8 +90,6 @@ public class AlphabeticalAppsList {
         /** Section & App properties */
         // The section for this item
         public SectionInfo sectionInfo;
-        // The row that this item shows up on
-        public int rowIndex;
 
         /** App-only properties */
         // The section name of this app.  Note that there can be multiple items with different
@@ -94,6 +97,8 @@ public class AlphabeticalAppsList {
         public String sectionName = null;
         // The index of this app in the section
         public int sectionAppIndex = -1;
+        // The row that this item shows up on
+        public int rowIndex;
         // The index of this app in the row
         public int rowAppIndex;
         // The associated AppInfo for the app
@@ -188,7 +193,6 @@ public class AlphabeticalAppsList {
     private int mNumAppsPerRow;
     private int mNumPredictedAppsPerRow;
     private int mNumAppRowsInAdapter;
-    private boolean mDisableEmptyText;
 
     public AlphabeticalAppsList(Context context) {
         mLauncher = (Launcher) context;
@@ -216,13 +220,6 @@ public class AlphabeticalAppsList {
     }
 
     /**
-     * Disables the empty text message when there are no search results.
-     */
-    public void disableEmptyText() {
-        mDisableEmptyText = true;
-    }
-
-    /**
      * Returns all the apps.
      */
     public List<AppInfo> getApps() {
@@ -523,18 +520,36 @@ public class AlphabeticalAppsList {
             }
             mNumAppRowsInAdapter = rowIndex + 1;
 
-            // Pre-calculate all the fast scroller fractions based on the number of rows
-            float rowFraction = 1f / mNumAppRowsInAdapter;
-            for (FastScrollSectionInfo info : mFastScrollerSections) {
-                AdapterItem item = info.fastScrollToItem;
-                if (item.viewType != AllAppsGridAdapter.ICON_VIEW_TYPE &&
-                        item.viewType != AllAppsGridAdapter.PREDICTION_ICON_VIEW_TYPE) {
-                    info.touchFraction = 0f;
-                    continue;
-                }
-
-                float subRowFraction = item.rowAppIndex * (rowFraction / mNumAppsPerRow);
-                info.touchFraction = item.rowIndex * rowFraction + subRowFraction;
+            // Pre-calculate all the fast scroller fractions
+            switch (mFastScrollDistributionMode) {
+                case FAST_SCROLL_FRACTION_DISTRIBUTE_BY_ROWS_FRACTION:
+                    float rowFraction = 1f / mNumAppRowsInAdapter;
+                    for (FastScrollSectionInfo info : mFastScrollerSections) {
+                        AdapterItem item = info.fastScrollToItem;
+                        if (item.viewType != AllAppsGridAdapter.ICON_VIEW_TYPE &&
+                                item.viewType != AllAppsGridAdapter.PREDICTION_ICON_VIEW_TYPE) {
+                            info.touchFraction = 0f;
+                            continue;
+                        }
+
+                        float subRowFraction = item.rowAppIndex * (rowFraction / mNumAppsPerRow);
+                        info.touchFraction = item.rowIndex * rowFraction + subRowFraction;
+                    }
+                    break;
+                case FAST_SCROLL_FRACTION_DISTRIBUTE_BY_NUM_SECTIONS:
+                    float perSectionTouchFraction = 1f / mFastScrollerSections.size();
+                    float cumulativeTouchFraction = 0f;
+                    for (FastScrollSectionInfo info : mFastScrollerSections) {
+                        AdapterItem item = info.fastScrollToItem;
+                        if (item.viewType != AllAppsGridAdapter.ICON_VIEW_TYPE &&
+                                item.viewType != AllAppsGridAdapter.PREDICTION_ICON_VIEW_TYPE) {
+                            info.touchFraction = 0f;
+                            continue;
+                        }
+                        info.touchFraction = cumulativeTouchFraction;
+                        cumulativeTouchFraction += perSectionTouchFraction;
+                    }
+                    break;
             }
         }
 
diff --git a/src/com/android/launcher3/widget/WidgetsRecyclerView.java b/src/com/android/launcher3/widget/WidgetsRecyclerView.java
index 61e63cdb7..e586dc253 100644
--- a/src/com/android/launcher3/widget/WidgetsRecyclerView.java
+++ b/src/com/android/launcher3/widget/WidgetsRecyclerView.java
@@ -102,7 +102,7 @@ public class WidgetsRecyclerView extends BaseRecyclerView {
 
         getCurScrollState(mScrollPosState);
         float pos = rowCount * touchFraction;
-        int availableScrollHeight = getAvailableScrollHeight(rowCount, mScrollPosState.rowHeight, 0);
+        int availableScrollHeight = getAvailableScrollHeight(rowCount, mScrollPosState.rowHeight);
         LinearLayoutManager layoutManager = ((LinearLayoutManager) getLayoutManager());
         layoutManager.scrollToPositionWithOffset(0, (int) -(availableScrollHeight * touchFraction));
 
@@ -115,29 +115,29 @@ public class WidgetsRecyclerView extends BaseRecyclerView {
      * Updates the bounds for the scrollbar.
      */
     @Override
-    public void onUpdateScrollbar() {
+    public void onUpdateScrollbar(int dy) {
         int rowCount = mWidgets.getPackageSize();
 
         // Skip early if, there are no items.
         if (rowCount == 0) {
-            mScrollbar.setScrollbarThumbOffset(-1, -1);
+            mScrollbar.setThumbOffset(-1, -1);
             return;
         }
 
         // Skip early if, there no child laid out in the container.
         getCurScrollState(mScrollPosState);
         if (mScrollPosState.rowIndex < 0) {
-            mScrollbar.setScrollbarThumbOffset(-1, -1);
+            mScrollbar.setThumbOffset(-1, -1);
             return;
         }
 
-        synchronizeScrollBarThumbOffsetToViewScroll(mScrollPosState, rowCount, 0);
+        synchronizeScrollBarThumbOffsetToViewScroll(mScrollPosState, rowCount);
     }
 
     /**
      * Returns the current scroll state.
      */
-    private void getCurScrollState(ScrollPositionState stateOut) {
+    protected void getCurScrollState(ScrollPositionState stateOut) {
         stateOut.rowIndex = -1;
         stateOut.rowTopOffset = -1;
         stateOut.rowHeight = -1;