/// A display link that keeps calling the `updateFrame` method on every screen refresh. 
private lazy var displayLink: CADisplayLink = { 
  self.isDisplayLinkInitialized = true 
  let displayLink = CADisplayLink(target: TargetProxy(target: self), selector: #selector(TargetProxy.onScreenUpdate)) 
  displayLink.add(to: .main, forMode: self.runLoopMode) 
  displayLink.isPaused = true 
  return displayLink 
}() 

public var priority: Float { 
    get { 
      return internalTask.priority 
    } 
    set { 
      internalTask.priority = newValue 
    } 
  } 

/* 
 用到时再加载 
 多次使用只加载一次 
 */ 
lazy var names :[String] = { 
  let names = ["why", "lmj", "swd"] 
  print("------") 按理说应该只打印一次 
  return names 
}() 
 
//方式一：仅仅创建button 
lazy var btn1:UIButton = UIButton() 
 
//方式二:可以设置更多btn的属性 
lazy var btn :UIButton = { 
  let btn = UIButton() 
  btn.setTitle("按钮", for: .normal) 
  btn.setImage(UIImage(named:""), for: .normal) 
  return btn 
}() 

//MARK: 点击事件 
func buttonClick(_ sender:UIButton) 
{ 
   print("----\(names.count)") 
} 

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