/**
* Updates the scrollbar thumb offset to match the visible scroll of the recycler view. It does
* this by mapping the available scroll area of the recycler view to the available space for the
* scroll bar.
*
* @param scrollPosState the current scroll position
* @param rowCount the number of rows, used to calculate the total scroll height (assumes that all
* rows are the same height)
* @param yOffset the offset to start tracking in the recycler view (only used for all apps)
*/
protected void synchronizeScrollBarThumbOffsetToViewScroll(
ScrollPositionState scrollPosState, int rowCount, int yOffset) {
int availableScrollHeight =
getAvailableScrollHeight(rowCount, scrollPosState.rowHeight, yOffset);
int availableScrollBarHeight = getAvailableScrollBarHeight();
// Only show the scrollbar if there is height to be scrolled
if (availableScrollHeight <= 0) {
mScrollbar.setScrollbarThumbOffset(-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()
+ yOffset
+ (scrollPosState.rowIndex * scrollPosState.rowHeight)
- scrollPosState.rowTopOffset;
int scrollBarY =
mBackgroundPadding.top
+ (int) (((float) scrollY / availableScrollHeight) * availableScrollBarHeight);
// Calculate the position and size of the scroll bar
int scrollBarX;
if (Utilities.isRtl(getResources())) {
scrollBarX = mBackgroundPadding.left;
} else {
scrollBarX = getWidth() - mBackgroundPadding.right - mScrollbar.getWidth();
}
mScrollbar.setScrollbarThumbOffset(scrollBarX, scrollBarY);
}
/**
* Handles the touch event and determines whether to show the fast scroller (or updates it if it
* is already showing).
*/
private boolean handleTouchEvent(MotionEvent ev) {
int action = ev.getAction();
int x = (int) ev.getX();
int y = (int) ev.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
// Keep track of the down positions
mDownX = x;
mDownY = mLastY = y;
if (shouldStopScroll(ev)) {
stopScroll();
}
mScrollbar.handleTouchEvent(ev, mDownX, mDownY, mLastY);
break;
case MotionEvent.ACTION_MOVE:
mLastY = y;
mScrollbar.handleTouchEvent(ev, mDownX, mDownY, mLastY);
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
onFastScrollCompleted();
mScrollbar.handleTouchEvent(ev, mDownX, mDownY, mLastY);
break;
}
return mScrollbar.isDragging();
}
@Override
protected void dispatchDraw(Canvas canvas) {
super.dispatchDraw(canvas);
onUpdateScrollbar();
mScrollbar.draw(canvas);
}
/**
* Returns the available scroll bar height: AvailableScrollBarHeight = Total height of the visible
* view - thumb height
*/
protected int getAvailableScrollBarHeight() {
int visibleHeight = getHeight() - mBackgroundPadding.top - mBackgroundPadding.bottom;
int availableScrollBarHeight = visibleHeight - mScrollbar.getThumbHeight();
return availableScrollBarHeight;
}
/** Returns the scroll bar width when the user is scrolling. */
public int getMaxScrollbarWidth() {
return mScrollbar.getThumbMaxWidth();
}
