也许你在写OC的时候已经用过了Masonry这个第三方库来写自动布局，今天我们来说说Swift版本的Masonry第三方库SnapKit

snp_remakeConstraints

snp_remakeConstraints is similar to snp_makeConstraints, but will first remove all existing constraints installed by SnapKit.

移除之前的所有约束，然后添加新约束的方法是：snp_makeConstraints

效果图：

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初始化 button

var button: UIButton!    var isExpanded = false        button = UIButton(type: UIButtonType.System)       button.setTitle("点击展开", forState: .Normal)       button.layer.borderWidth = 3       button.layer.borderColor = UIColor.redColor().CGColor       button.backgroundColor = UIColor.greenColor()       button.addTarget(self, action: "change", forControlEvents: UIControlEvents.TouchUpInside)       view.addSubview(button)

重写方法

override func updateViewConstraints() {// 这里使用update也是一样的。// remake会将之前的全部移除，然后重新添加      button.snp_remakeConstraints { (make) -> Void in          make.top.leading.trailing.equalTo(view)          if isExpanded {              make.bottom.equalTo(view)          }else {              make.bottom.equalTo(-300)          }      }      super.updateViewConstraints()  }

按钮方法

func change() {      isExpanded = !isExpanded      if !isExpanded {          button.setTitle("点击展开", forState: .Normal)      }else {          button.setTitle("点击收起", forState: .Normal)      }      self.view.setNeedsUpdateConstraints()      self.view.updateConstraintsIfNeeded()      UIView.animateWithDuration(0.5) { () -> Void in          self.view.layoutIfNeeded()      }  }