如何最好地优化 NSLayoutConstraint？

Question

同事们，

我开发了一个自定义键盘。在键盘类型（字母、数字、特殊字符）之间切换的速度存在问题。这是因为每次按钮都会重新绘制。 NSLayoutConstraint 我设置如下：

1. 有一个类 KeyboardViewController。他添加到他的 KeyboardView

       let left = NSLayoutConstraint(item: self.keyboardView, attribute: .Left, relatedBy: .Equal,
               toItem: self.view, attribute: .Left, multiplier: 1.0, constant: 0.0)
           let top = NSLayoutConstraint(item: self.keyboardView, attribute: .Top, relatedBy: .Equal,
               toItem: placeForSuggestion!, attribute: .Bottom, multiplier: 1.0, constant: 0.0)
           let right = NSLayoutConstraint(item: self.keyboardView, attribute: .Right, relatedBy: .Equal,
               toItem: self.view, attribute: .Right, multiplier: 1.0, constant: 0.0)
           let bottom = NSLayoutConstraint(item: self.keyboardView, attribute: .Bottom, relatedBy: .Equal,
               toItem: self.view, attribute: .Bottom, multiplier: 1.0, constant: 0.0)
           let height = NSLayoutConstraint(item: self.keyboardView, attribute: .Height, relatedBy: .Equal,
               toItem: self.view, attribute: .Height, multiplier: 1.0, constant: 216)
           left.priority = 999
           right.priority = 999
           bottom.priority = 999
           top.priority = 999
           height.priority = 999
           self.view.addConstraints([left, right, top, bottom, height])
   

2. 在KeyboardView类中，按钮添加如下：

   super.updateConstraints()
   
   if !layoutConstrained {
   
       var lastRowView: UIView? = nil
       for (rowIndex, keyRow) in keyRows.enumerate() {
           var lastKeyView: UIView? = nil
           for (keyIndex, key) in keyRow.enumerate() {
   
               var relativeWidth: CGFloat = 0.0;
               switch key.type! {
               case .ModeChange:
                   relativeWidth = 0.92/8
               case .KeyboardChange:
                   relativeWidth = 0.92/8
               case .Space:
                   relativeWidth = 3.92/8
               case .Return:
                   relativeWidth = 1.84/8
               default:
                   relativeWidth = 0.0
               }
   
               key.translatesAutoresizingMaskIntoConstraints = false
   
               if let lastView = lastKeyView {
                   let left: NSLayoutConstraint!
                   if (key.keyCap == "Z" || (key.keyCap == "backspace" && keyRow[keyIndex - 1].keyCap == "M")) {
                       left = NSLayoutConstraint(item: key, attribute: .Left, relatedBy: .Equal,
                           toItem: lastView, attribute: .Right, multiplier: 1.0, constant: englishMZSpace)
                   } else {
                       left = NSLayoutConstraint(item: key, attribute: .Left, relatedBy: .Equal,
                           toItem: lastView, attribute: .Right, multiplier: 1.0, constant: distanceBetweenKeys)
                   }
                   let top = NSLayoutConstraint(item: key, attribute: .Top, relatedBy: .Equal,
                       toItem: lastView, attribute: .Top, multiplier: 1.0, constant: 0.0)
                   let bottom = NSLayoutConstraint(item: key, attribute: .Bottom, relatedBy: .Equal,
                       toItem: lastView, attribute: .Bottom, multiplier: 1.0, constant: 0.0)
                   var width: NSLayoutConstraint?
                   if relativeWidth == 0.0 {
                       width = NSLayoutConstraint(item: key, attribute: .Width, relatedBy: .Equal,
                           toItem: lastView, attribute: .Width, multiplier: 1.0, constant: 0.0)
                   } else {
                       width = NSLayoutConstraint(item: key, attribute: .Width, relatedBy: .Equal,
                           toItem: self, attribute: .Width, multiplier: relativeWidth, constant: 0.0)
                   }
                   self.addConstraints([left, top, bottom, width!])
               } else {
                   let leftEdge: NSLayoutConstraint
                   if key.keyCap == "A" {
                       leftEdge = NSLayoutConstraint(item: key, attribute: .Left, relatedBy: .Equal,
                           toItem: self, attribute: .Left, multiplier: 1.0, constant: englishALSpace)
                   } else {
                       leftEdge = NSLayoutConstraint(item: key, attribute: .Left, relatedBy: .Equal,
                           toItem: self, attribute: .Left, multiplier: 1.0, constant: leftRightSpace)
                   }
   
                   self.addConstraint(leftEdge)
   
                   if let lastRow = lastRowView {
                       let top = NSLayoutConstraint(item: key, attribute: .Top, relatedBy:.Equal,
                           toItem: lastRow, attribute: .Bottom, multiplier: 1.0, constant: rowTopInset)
                       let height = NSLayoutConstraint(item: key, attribute: .Height, relatedBy: .Equal,
                           toItem: lastRow, attribute: .Height, multiplier: 1.0, constant: 0.0)
   
                       self.addConstraints([top, height])
                   } else {
                       let topEdge =  NSLayoutConstraint(item: key, attribute: .Top, relatedBy:.Equal,
                           toItem: self, attribute: .Top, multiplier: 1.0, constant: rowTopInset)
   
                       self.addConstraint(topEdge)
                   }
   
                   if rowIndex == keyRows.count - 1 {
                       let bottomEdge = NSLayoutConstraint(item: key, attribute: .Bottom, relatedBy: .Equal,
                           toItem: self, attribute: .Bottom, multiplier: 1.0, constant: -rowBottomInset)
                       self.addConstraint(bottomEdge)
                   }
   
                   lastRowView = key
               }
   
               if keyIndex == keyRow.count - 1 {
                   let rightEdge: NSLayoutConstraint
                   if key.keyCap == "L" {
                       rightEdge = NSLayoutConstraint(item: key, attribute: .Right, relatedBy: .Equal,
                           toItem: self, attribute: .Right, multiplier: 1.0, constant: -englishALSpace)
                   } else {
                       rightEdge = NSLayoutConstraint(item: key, attribute: .Right, relatedBy: .Equal,
                           toItem: self, attribute: .Right, multiplier: 1.0, constant: -leftRightSpace)
                   }
                   self.addConstraint(rightEdge)
               }
   
               lastKeyView = key
           }
       }
       layoutConstrained = true
   }
   

我看到了 2 种优化变体：

1. 第一次运行后缓存所有的NSLayoutConstraint
2. 使用 CGRectMake 代替 NSLayoutConstraint

您或许可以提供更多相关选项？

在本视频中，我尝试切换键盘并快速打印https://yadi.sk/i/36YxEwgtmHJVd

Answer 1

在视频中对我来说似乎很快。

但是，我建议不要每次都重新创建布局约束，而是为每种键盘类型创建一次，然后在现有键盘之间切换。关于不应该是内存问题的小视图，这比一直重新创建和删除约束要好得多。

或者，如果关键数量保持（几乎）相同，您可以只更改约束的值，甚至为关键位置的变化设置动画以获得可能不错的效果。