iOS 滑动标签居中的方法

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很久之前的一个小算法,在这里MARK一下

func selectLabelCenter() {
//计算选中label的centerX
        let centerX = CGFloat(self.segmentControl.selectedSegmentIndex)*itemWidth + itemWidth/2
//计算出应该偏移的offsetX
        var needScrollowOffsetX = centerX - slidingView.width/2
//最小值不能小于0
        if needScrollowOffsetX < 0{
            needScrollowOffsetX = 0
        }
//不能大于最大值(滑动至最右侧)
        let maxScrollowOffsetX = slidingView.contentSize.width-slidingView.width
        if needScrollowOffsetX > maxScrollowOffsetX {
            needScrollowOffsetX = maxScrollowOffsetX
        }
//不需要滑动时不用滑动
        if needScrollowOffsetX != slidingView.contentOffset.x {
            slidingView.isUserInteractionEnabled = false
            UIView.animate(withDuration: 1.0, animations: {
                self.slidingView.contentOffset = CGPoint(x: needScrollowOffsetX, y: 0)
            }, completion: { (_) in
                self.slidingView.isUserInteractionEnabled = true
            })
        }
    }