判断uiscrollView滑到底部

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-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
    CGPoint offset = scrollView.contentOffset;  // 当前滚动位移
    CGRect bounds = scrollView.bounds;          // UIScrollView 可视高度
    CGSize size = scrollView.contentSize;         // 滚动区域
    UIEdgeInsets inset = scrollView.contentInset;
    float y = offset.y + bounds.size.height - inset.bottom;
    float h = size.height;

    float reload_distance = 10;
    if (y > (h + reload_distance)) {
        [self requestProductList];
    }
}