iOS平滑的下拉加载更多数据

- (void)setContentSize:(CGSize)contentSize
{
if (!CGSizeEqualToSize(self.contentSize, CGSizeZero))
{
if (contentSize.height > self.contentSize.height)
{
CGPoint offset = self.contentOffset;
offset.y += (contentSize.height - self.contentSize.height);
self.contentOffset = offset;
}
}
[super setContentSize:contentSize];
}