为autoLayout 增加标识符，方便调试



如上图，是一个十分简单的布局。 root view 上加了一个 button 和一个 webview。

不加标识符的样子

1. 视图层级中没有标识
   
   只有 UIView、WKWebView 之类，如果view很多，就很难分得清。

2. 约束没有标识符 

   只知道 uiview 和uibutton 中心对齐，不知道哪个view 和哪个 button。

3. autoLayout 日志中没有标识符

   (lldb) po [0x7f8aaa50e6d0 _autolayoutTrace]
   
   •UIWindow:0x7f8aaa60a1b0
   |   •UIView:0x7f8aaa502c30
   |   |   *_UILayoutGuide:0x7f8aaa50d140
   |   |   *_UILayoutGuide:0x7f8aaa50d750
   |   |   *UIButton:0x7f8aaa50e6d0'click to send'
   |   |   |   UIButtonLabel:0x7f8aaa6073b0'click to send'
   |   |   *WKWebView:0x7f8aaa851000
   |   |   |   WKScrollView:0x7f8aaa853a00
   |   |   |   |   WKContentView:0x7f8aaa83c400
   |   |   |   |   |   UIView:0x7f8aaa706350
   |   |   |   |   |   |   UIView:0x7f8aaa7002e0
   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa712200
   |   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa60ec10
   |   |   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa60edf0
   |   |   |   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa60f1b0
   |   |   |   |   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa60efd0
   |   |   |   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa60e850
   |   |   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa60e670
   |   |   |   |   |   |   |   |   WKCompositingView:0x7f8aaa60ea30
   |   |   |   |   UIView:0x7f8aaa7066b0
   |   |   |   |   UIImageView:0x7f8aaa70ce00
   |   |   |   |   UIImageView:0x7f8aaa70cbd0
   
   Legend:
       * - is laid out with auto layout
       + - is laid out manually, but is represented in the layout engine because translatesAutoresizingMaskIntoConstraints = YES
       • - layout engine host
   
   (lldb) po [0x7f8aaa50e6d0 constraintsAffectingLayoutForAxis:0]
   <__NSArrayI 0x600000f3aa30>(
   <NSContentSizeLayoutConstraint:0x6000025ac2a0 UIButton:0x7f8aaa50e6d0'click to send'.width == 102 Hug:250 CompressionResistance:750   (active)>,
   <SnapKit.LayoutConstraint:0x6000025a7420@ViewController.swift#26 UIButton:0x7f8aaa50e6d0.centerX == UIView:0x7f8aaa502c30.centerX>,
   <NSLayoutConstraint:0x600002289270 'UIView-Encapsulated-Layout-Width' UIView:0x7f8aaa502c30.width == 375   (active)>
   

   )

为约束增加标识符

    button.snp.makeConstraints { (make) in
        make.centerX.equalToSuperview().labeled("mybutton centerX")
        make.top.equalToSuperview().offset(50).labeled("mybutton top")
    }

    webView.snp.makeConstraints({ (make) in
        make.leading.trailing.bottom.equalToSuperview().labeled("mywebview Edges")
        make.top.equalToSuperview().offset(200).labeled("mywebview Top")
    })

效果

视图层级中，可以看到约束的标识符了。 

选中约束之后，可以看到 Identifier了



layout日志中，可以看到标识符了 

为 view 设置 accessibilityIdentifier 属性

view.accessibilityIdentifier = "rootView abi"
button.accessibilityIdentifier = "mybtn abi"
webView.accessibilityIdentifier = "mywebview abi"

效果

layout 日志中可以看到 



但是 snapKit 约束的描述，设置的accessibilityIdentifier 没有作用。

增加 accessibilityLabel



在视图层级中，可以看到

总结

• 设置约束的标识符，无论是 SnapKit，还是系统原生的
• 设置 accessibilityIdentifier 属性，在日志中可以帮助定位问题
• 设置 accessibilityLabel 属性，帮助查看视图成绩