private void updateHeader(int headerPosition) {
// check if there is a new header should be sticky
if (mHeaderPosition == null || mHeaderPosition != headerPosition) {
mHeaderPosition = headerPosition;
final long headerId = mAdapter.getHeaderId(headerPosition);
if (mHeaderId == null || mHeaderId != headerId) {
mHeaderId = headerId;
final View header = mAdapter.getHeaderView(mHeaderPosition, mHeader, this);
if (mHeader != header) {
if (header == null) {
throw new NullPointerException("header may not be null");
}
swapHeader(header);
}
ensureHeaderHasCorrectLayoutParams(mHeader);
measureHeader(mHeader);
if (mOnStickyHeaderChangedListener != null) {
mOnStickyHeaderChangedListener.onStickyHeaderChanged(
this, mHeader, headerPosition, mHeaderId);
}
// Reset mHeaderOffset to null ensuring
// that it will be set on the header and
// not skipped for performance reasons.
mHeaderOffset = null;
}
}
int headerOffset = 0;
// Calculate new header offset
// Skip looking at the first view. it never matters because it always
// results in a headerOffset = 0
int headerBottom = mHeader.getMeasuredHeight() + stickyHeaderTop();
for (int i = 0; i < mList.getChildCount(); i++) {
final View child = mList.getChildAt(i);
final boolean doesChildHaveHeader =
child instanceof WrapperView && ((WrapperView) child).hasHeader();
final boolean isChildFooter = mList.containsFooterView(child);
if (child.getTop() >= stickyHeaderTop() && (doesChildHaveHeader || isChildFooter)) {
headerOffset = Math.min(child.getTop() - headerBottom, 0);
break;
}
}
setHeaderOffet(headerOffset);
if (!mIsDrawingListUnderStickyHeader) {
mList.setTopClippingLength(mHeader.getMeasuredHeight() + mHeaderOffset);
}
updateHeaderVisibilities();
}
// Reset values tied the header. also remove header form layout
// This is called in response to the data set or the adapter changing
private void clearHeader() {
if (mHeader != null) {
removeView(mHeader);
mHeader = null;
mHeaderId = null;
mHeaderPosition = null;
mHeaderOffset = null;
// reset the top clipping length
mList.setTopClippingLength(0);
updateHeaderVisibilities();
}
}
public void setDrawingListUnderStickyHeader(boolean drawingListUnderStickyHeader) {
mIsDrawingListUnderStickyHeader = drawingListUnderStickyHeader;
// reset the top clipping length
mList.setTopClippingLength(0);
}