//主要代码
-
(void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
CGFloat x = targetContentOffset->x;
CGFloat pageWidth = itemWidth + 20;
CGFloat movedX = x - pageWidth * selectedIndex;
if (movedX < -pageWidth * 0.5) {
// Move left
selectedIndex--;
} else if (movedX > pageWidth * 0.5) {
// Move right
selectedIndex++;
}if (ABS(velocity.x) >= 2){
targetContentOffset->x = pageWidth * selectedIndex;
} else {
targetContentOffset->x = scrollView.contentOffset.x;
[scrollView setContentOffset:CGPointMake(pageWidth * selectedIndex, scrollView.contentOffset.y) animated:YES];
}
NSLog(@"%ld",selectedIndex);
}