protected override void OnScrollChanged(int l, int t, int oldl, int oldt)
{
base.OnScrollChanged(l, t, oldl, oldt);
if (_mCallbacks != null)
{
if (ChildCount > 0)
{
int firstVisiblePosition = GetChildAdapterPosition(GetChildAt(0));
int lastVisiblePosition = GetChildAdapterPosition(GetChildAt(ChildCount - 1));
for (int i = firstVisiblePosition, j = 0; i <= lastVisiblePosition; i++, j++)
{
int childHeight = 0;
View child = GetChildAt(j);
if (child != null)
{
if (_mChildrenHeights.IndexOfKey(i) < 0 || (child.Height != _mChildrenHeights.Get(i)))
{
childHeight = child.Height;
}
}
_mChildrenHeights.Put(i, childHeight);
}
View firstVisibleChild = GetChildAt(0);
if (firstVisibleChild != null)
{
if (_mPrevFirstVisiblePosition < firstVisiblePosition)
{
// scroll down
int skippedChildrenHeight = 0;
if (firstVisiblePosition - _mPrevFirstVisiblePosition != 1)
{
for (int i = firstVisiblePosition - 1; i > _mPrevFirstVisiblePosition; i--)
{
if (0 < _mChildrenHeights.IndexOfKey(i))
{
skippedChildrenHeight += _mChildrenHeights.Get(i);
}
else
{
// Approximate each item's height to the first visible child.
// It may be incorrect, but without this, scrollY will be broken
// when scrolling from the bottom.
skippedChildrenHeight += firstVisibleChild.Height;
}
}
}
_mPrevScrolledChildrenHeight += _mPrevFirstVisibleChildHeight + skippedChildrenHeight;
_mPrevFirstVisibleChildHeight = firstVisibleChild.Height;
}
else if (firstVisiblePosition < _mPrevFirstVisiblePosition)
{
// scroll up
int skippedChildrenHeight = 0;
if (_mPrevFirstVisiblePosition - firstVisiblePosition != 1)
{
for (int i = _mPrevFirstVisiblePosition - 1; i > firstVisiblePosition; i--)
{
if (0 < _mChildrenHeights.IndexOfKey(i))
{
skippedChildrenHeight += _mChildrenHeights.Get(i);
}
else
{
// Approximate each item's height to the first visible child.
// It may be incorrect, but without this, scrollY will be broken
// when scrolling from the bottom.
skippedChildrenHeight += firstVisibleChild.Height;
}
}
}
_mPrevScrolledChildrenHeight -= firstVisibleChild.Height + skippedChildrenHeight;
_mPrevFirstVisibleChildHeight = firstVisibleChild.Height;
}
else if (firstVisiblePosition == 0)
{
_mPrevFirstVisibleChildHeight = firstVisibleChild.Height;
_mPrevScrolledChildrenHeight = 0;
}
if (_mPrevFirstVisibleChildHeight < 0)
{
_mPrevFirstVisibleChildHeight = 0;
}
_mScrollY = _mPrevScrolledChildrenHeight - firstVisibleChild.Top;
_mPrevFirstVisiblePosition = firstVisiblePosition;
_mCallbacks.OnScrollChanged(_mScrollY, _mFirstScroll, _mDragging);
if (_mFirstScroll)
{
_mFirstScroll = false;
}
if (_mPrevScrollY < _mScrollY)
{
//down
_mScrollState = ObservableScrollState.Up;
}
else if (_mScrollY < _mPrevScrollY)
{
//up
_mScrollState = ObservableScrollState.Down;
}
else
{
_mScrollState = ObservableScrollState.Stop;
}
_mPrevScrollY = _mScrollY;
}
}
}
}
private void OnScrollChanged()
{
if (_mCallbacks != null)
{
if (ChildCount > 0)
{
int firstVisiblePosition = FirstVisiblePosition;
for (int i = FirstVisiblePosition, j = 0; i <= LastVisiblePosition; i++, j++)
{
if (_mChildrenHeights.IndexOfKey(i) < 0 || GetChildAt(j).Height != _mChildrenHeights.Get(i))
{
if (i % GetNumColumnsCompat() == 0)
{
_mChildrenHeights.Put(i, GetChildAt(j).Height);
}
}
}
View firstVisibleChild = GetChildAt(0);
if (firstVisibleChild != null)
{
if (_mPrevFirstVisiblePosition < firstVisiblePosition)
{
// scroll down
int skippedChildrenHeight = 0;
if (firstVisiblePosition - _mPrevFirstVisiblePosition != 1)
{
for (int i = firstVisiblePosition - 1; i > _mPrevFirstVisiblePosition; i--)
{
if (0 < _mChildrenHeights.IndexOfKey(i))
{
skippedChildrenHeight += _mChildrenHeights.Get(i);
}
}
}
_mPrevScrolledChildrenHeight += _mPrevFirstVisibleChildHeight + skippedChildrenHeight;
_mPrevFirstVisibleChildHeight = firstVisibleChild.Height;
}
else if (firstVisiblePosition < _mPrevFirstVisiblePosition)
{
// scroll up
int skippedChildrenHeight = 0;
if (_mPrevFirstVisiblePosition - firstVisiblePosition != 1)
{
for (int i = _mPrevFirstVisiblePosition - 1; i > firstVisiblePosition; i--)
{
if (0 < _mChildrenHeights.IndexOfKey(i))
{
skippedChildrenHeight += _mChildrenHeights.Get(i);
}
}
}
_mPrevScrolledChildrenHeight -= firstVisibleChild.Height + skippedChildrenHeight;
_mPrevFirstVisibleChildHeight = firstVisibleChild.Height;
}
else if (firstVisiblePosition == 0)
{
_mPrevFirstVisibleChildHeight = firstVisibleChild.Height;
}
if (_mPrevFirstVisibleChildHeight < 0)
{
_mPrevFirstVisibleChildHeight = 0;
}
_mScrollY = _mPrevScrolledChildrenHeight - firstVisibleChild.Top;
_mPrevFirstVisiblePosition = firstVisiblePosition;
_mCallbacks.OnScrollChanged(_mScrollY, _mFirstScroll, _mDragging);
if (_mFirstScroll)
{
_mFirstScroll = false;
}
if (_mPrevScrollY < _mScrollY)
{
_mScrollState = ObservableScrollState.Up;
}
else if (_mScrollY < _mPrevScrollY)
{
_mScrollState = ObservableScrollState.Down;
}
else
{
_mScrollState = ObservableScrollState.Stop;
}
_mPrevScrollY = _mScrollY;
}
}
}
}
