private int determineTargetPage(float pageOffset, int velocity, int deltaX) {
int targetPage = mCurItem;
if (Math.abs(deltaX) > mFlingDistance && Math.abs(velocity) > mMinimumVelocity) {
if (velocity > 0 && deltaX > 0) {
targetPage -= 1;
} else if (velocity < 0 && deltaX < 0) {
targetPage += 1;
}
} else {
targetPage = (int) Math.round(mCurItem + pageOffset);
}
return targetPage;
}
/**
* Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
*
* @param x the number of pixels to scroll by on the X axis
* @param y the number of pixels to scroll by on the Y axis
* @param velocity the velocity associated with a fling, if applicable. (0 otherwise)
*/
void smoothScrollTo(int x, int y, int velocity) {
if (getChildCount() == 0) {
// Nothing to do.
setScrollingCacheEnabled(false);
return;
}
int sx = getScrollX();
int sy = getScrollY();
int dx = x - sx;
int dy = y - sy;
if (dx == 0 && dy == 0) {
completeScroll();
if (isMenuOpen()) {
if (mOpenedListener != null) mOpenedListener.onOpened();
} else {
if (mClosedListener != null) mClosedListener.onClosed();
}
return;
}
setScrollingCacheEnabled(true);
mScrolling = true;
final int width = getBehindWidth();
final int halfWidth = width / 2;
final float distanceRatio = Math.min(1f, 1.0f * Math.abs(dx) / width);
final float distance = halfWidth + halfWidth * distanceInfluenceForSnapDuration(distanceRatio);
int duration = 0;
velocity = Math.abs(velocity);
if (velocity > 0) {
duration = 4 * Math.round(1000 * Math.abs(distance / velocity));
} else {
final float pageDelta = (float) Math.abs(dx) / width;
duration = (int) ((pageDelta + 1) * 100);
duration = MAX_SETTLE_DURATION;
}
duration = Math.min(duration, MAX_SETTLE_DURATION);
mScroller.startScroll(sx, sy, dx, dy, duration);
invalidate();
}