1 files changed, 59 insertions, 9 deletions

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;
         }