1.NSLayoutConstraint 设置优先级 2.删除更新约束(添加标识)

 //显示提交按钮 时的约束

    private var svBottomCon:NSLayoutConstraint?
    
    //隐藏提交按钮 时的约束
    private var svUpdateBottomCon:NSLayoutConstraint?


    //显示有数据的UI ， 不能编辑,隐藏提交按钮  此时设至 高约束等级 defaultHigh 

 func showDataUI(){ 

　　　　bindCardView.updateTempUI() 
　　　　self.submitBtn.isHidden = true 
　　　　if #available(iOS 11.0, *) { 
　　　　　　　svUpdateBottomCon = scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -20)
 　　　　} else {
　　　　 　　svUpdateBottomCon = scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -20)
　　　　}

 　　　　svUpdateBottomCon?.priority = UILayoutPriority.defaultHigh svUpdateBottomCon?.isActive = true 
　}
 
//默认UI 设置 第一次的约束等级是defaultLow

　　if #available(iOS 11.0, *) { 
　　　　scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20).isActive = true 
　　　　svBottomCon = scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -102) 
　　　　submitBtn.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -30).isActive = true 
　　　　} else { 
　　　　scrollView.topAnchor.constraint(equalTo: view.topAnchor, constant: 20).isActive = true
　　　　svBottomCon = scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -102) 
　　　　submitBtn.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -30).isActive = true 
　　　} 
　　　　
　　　svBottomCon?.priority = UILayoutPriority.defaultLow 
　　　svBottomCon?.isActive = true

 

 

删除约束 操作：可以查看  源码：

https://github.com/jiyongTeam/JYFilterView

1. 给约束添加标识

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// 每个的约束,追加identifier let topConstraint =  currentItem.topAnchor.constraint(equalTo: self.itemsContainerView.topAnchor, constant: (itemHeight + itemYSpacing) * CGFloat(i)) topConstraint.identifier = "JYFilterItemView" topConstraint.isActive = true let widthConstraint = currentItem.widthAnchor.constraint(equalTo: self.itemsContainerView.widthAnchor, multiplier: itemWidthScale, constant:  -spacingItemGapWidth) widthConstraint.identifier = "JYFilterItemView" widthConstraint.isActive = true let heightConstraint = currentItem.heightAnchor.constraint(equalToConstant: itemHeight) heightConstraint.identifier = "JYFilterItemView" heightConstraint.isActive = true if lastItem == nil{     let leftConstraint =         currentItem.leftAnchor.constraint(equalTo: self.itemsContainerView.leftAnchor, constant: horizontalMagin)     leftConstraint.identifier = "JYFilterItemView"     leftConstraint.isActive = true }else{     let leftConstraint = currentItem.leftAnchor.constraint(equalTo: (lastItem?.rightAnchor)!, constant: itemXSpacing)     leftConstraint.identifier = "JYFilterItemView"     leftConstraint.isActive = true } // 最后一行 if i == rows - 1{     let bottomConstraint = currentItem.bottomAnchor.constraint(equalTo: self.itemsContainerView.bottomAnchor, constant: 0)     bottomConstraint.identifier = "JYFilterItemView"     bottomConstraint.isActive = true }

　　

约束更新处理， 删除原来的约束

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//约束更新的处理: 删除子视图相关的所有约束 let associatedConstraints = itemsContainerView.constraints.filter {     $0.identifier == "JYFilterItemView" } NSLayoutConstraint.deactivate(associatedConstraints) itemsContainerView.removeConstraints(associatedConstraints)   itemViewList.forEach {     let itemConstraints = $0.constraints.filter {         $0.identifier == "JYFilterItemView"     }     NSLayoutConstraint.deactivate(itemConstraints)     $0.removeConstraints(itemConstraints) }<br>　　　　　　<br>　　<br>　　　　　//业务逻辑 for item in itemViewList{     item.updateViewStyle(style.itemViewStyle) } configItems()