Don't allow apps to request scrolls to out-of-bounds positions

An app was requesting smooth scrolling to a view position beyond the
number of items in the list. This caused our setup logic to execute on
every frame, waiting for the target view to be added.

This fix clamps the requested target position to the number of items
actually in the list.

Issue #6572175 Messaging: Sometimes conversation doesn't scroll when focus is brought to the compose field

Change-Id: I23707aeb213e67af4297713a03c2f5b446c8e2b6

Author: chethaase

core/java/android/widget/AbsListView.java

@@ -4289,14 +4289,15 @@ void start(final int position) {
             final int lastPos = firstPos + childCount - 1;
 
             int viewTravelCount;
-            if (position < firstPos) {
-                viewTravelCount = firstPos - position + 1;
+            int clampedPosition = Math.max(0, Math.min(getCount() - 1, position));
+            if (clampedPosition < firstPos) {
+                viewTravelCount = firstPos - clampedPosition + 1;
                 mMode = MOVE_UP_POS;
-            } else if (position > lastPos) {
-                viewTravelCount = position - lastPos + 1;
+            } else if (clampedPosition > lastPos) {
+                viewTravelCount = clampedPosition - lastPos + 1;
                 mMode = MOVE_DOWN_POS;
             } else {
-                scrollToVisible(position, INVALID_POSITION, SCROLL_DURATION);
+                scrollToVisible(clampedPosition, INVALID_POSITION, SCROLL_DURATION);
                 return;
             }
 
@@ -4305,7 +4306,7 @@ void start(final int position) {
             } else {
                 mScrollDuration = SCROLL_DURATION;
             }
-            mTargetPos = position;
+            mTargetPos = clampedPosition;
             mBoundPos = INVALID_POSITION;
             mLastSeenPos = INVALID_POSITION;
 
@@ -4340,14 +4341,15 @@ void start(final int position, final int boundPosition) {
             final int lastPos = firstPos + childCount - 1;
 
             int viewTravelCount;
-            if (position < firstPos) {
+            int clampedPosition = Math.max(0, Math.min(getCount() - 1, position));
+            if (clampedPosition < firstPos) {
                 final int boundPosFromLast = lastPos - boundPosition;
                 if (boundPosFromLast < 1) {
                     // Moving would shift our bound position off the screen. Abort.
                     return;
                 }
 
-                final int posTravel = firstPos - position + 1;
+                final int posTravel = firstPos - clampedPosition + 1;
                 final int boundTravel = boundPosFromLast - 1;
                 if (boundTravel < posTravel) {
                     viewTravelCount = boundTravel;
@@ -4356,14 +4358,14 @@ void start(final int position, final int boundPosition) {
                     viewTravelCount = posTravel;
                     mMode = MOVE_UP_POS;
                 }
-            } else if (position > lastPos) {
+            } else if (clampedPosition > lastPos) {
                 final int boundPosFromFirst = boundPosition - firstPos;
                 if (boundPosFromFirst < 1) {
                     // Moving would shift our bound position off the screen. Abort.
                     return;
                 }
 
-                final int posTravel = position - lastPos + 1;
+                final int posTravel = clampedPosition - lastPos + 1;
                 final int boundTravel = boundPosFromFirst - 1;
                 if (boundTravel < posTravel) {
                     viewTravelCount = boundTravel;
@@ -4373,7 +4375,7 @@ void start(final int position, final int boundPosition) {
                     mMode = MOVE_DOWN_POS;
                 }
             } else {
-                scrollToVisible(position, boundPosition, SCROLL_DURATION);
+                scrollToVisible(clampedPosition, boundPosition, SCROLL_DURATION);
                 return;
             }
 
@@ -4382,7 +4384,7 @@ void start(final int position, final int boundPosition) {
             } else {
                 mScrollDuration = SCROLL_DURATION;
             }
-            mTargetPos = position;
+            mTargetPos = clampedPosition;
             mBoundPos = boundPosition;
             mLastSeenPos = INVALID_POSITION;
 
@@ -4415,7 +4417,7 @@ void startWithOffset(final int position, int offset, final int duration) {
 
             offset += getPaddingTop();
 
-            mTargetPos = position;
+            mTargetPos = Math.max(0, Math.min(getCount() - 1, position));
             mOffsetFromTop = offset;
             mBoundPos = INVALID_POSITION;
             mLastSeenPos = INVALID_POSITION;
@@ -4425,13 +4427,13 @@ void startWithOffset(final int position, int offset, final int duration) {
             final int lastPos = firstPos + childCount - 1;
 
             int viewTravelCount;
-            if (position < firstPos) {
-                viewTravelCount = firstPos - position;
-            } else if (position > lastPos) {
-                viewTravelCount = position - lastPos;
+            if (mTargetPos < firstPos) {
+                viewTravelCount = firstPos - mTargetPos;
+            } else if (mTargetPos > lastPos) {
+                viewTravelCount = mTargetPos - lastPos;
             } else {
                 // On-screen, just scroll.
-                final int targetTop = getChildAt(position - firstPos).getTop();
+                final int targetTop = getChildAt(mTargetPos - firstPos).getTop();
                 smoothScrollBy(targetTop - offset, duration, true);
                 return;
             }