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在uitableview里边重写setContentSize如下

- (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];}