I found part of the logic in AbsListView, which I've pasted below.
Note that the vertical scroll offset is calculated based on the
assumption that all the child Views will have the same height. In my
case the child Views are all different heights but I do have an array
that contains a list of those heights so it's easy to modify the math
to calculate the correct scroll offset for my case.
I'd like to modify the AbsListView class with two new protected
methods which can be overridden to allow proper behavior in my case.
The first would be boolean allChildViewsSameHeight(), which would
return true in the default case. The second would be int
getHeightOfChildAt( int childIndex ), which would return the height of
the first child as a default and could be overridden to return
different heights.
In addition, I'd like to modify the math below to use
getHeightOfChildAt in the case where allChildViewsSameHeight returns
false. What is the method to merge this change back into the main
source tree once I have tested it?
@Override
protected int computeVerticalScrollOffset() {
final int firstPosition = mFirstPosition;
final int childCount = getChildCount();
if (firstPosition >= 0 && childCount > 0) {
if (mSmoothScrollbarEnabled) {
final View view = getChildAt(0);
final int top = view.getTop();
int height = view.getHeight();
if (height > 0) {
return Math.max(firstPosition * 100 - (top *
100) / height +
(int)((float)mScrollY / getHeight() *
mItemCount * 100), 0);
}
} else {
int index;
final int count = mItemCount;
if (firstPosition == 0) {
index = 0;
} else if (firstPosition + childCount == count) {
index = count;
} else {
index = firstPosition + childCount / 2;
}
return (int) (firstPosition + childCount * (index /
(float) count));
}
}
return 0;
}
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