Swift 添加KVO

 

     
1.添加监听
   lab1.addObserver(self, forKeyPath: "text", options: [.new, .old], context: nil)



2. 监听
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if let old = change?[NSKeyValueChangeKey.oldKey] {
          print("old = \(old)") //
        }
              
        if let new = change?[NSKeyValueChangeKey.newKey] {
          print("new = \(new)") // Albert
        }
    }


3.移除KVO
    deinit {
        lab1.removeObserver(self, forKeyPath: "text")
    }

 

2.添加多个KVO

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lab1.addObserver(self, forKeyPath: "text", options: [.new, .old], context: nil)     lab1.addObserver(self, forKeyPath: "frame", options: .new, context: nil)       override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {     if keyPath == "text"{         print("text改变")     }else{         print("frame 改变")     }     if let old = change?[NSKeyValueChangeKey.oldKey] {       print("old = \(old)") //     }                 if let new = change?[NSKeyValueChangeKey.newKey] {       print("new = \(new)") // Albert     } }   deinit {     lab1.removeObserver(self, forKeyPath: "text")     lab1.removeObserver(self, forKeyPath: "frame") }

　　

 

3. 两个label 都监听了 text, frame

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lab1.addObserver(self, forKeyPath: "text", options: [.new, .old], context: nil)     lab1.addObserver(self, forKeyPath: "frame", options: .new, context: nil)           lab2.addObserver(self, forKeyPath: "text", options: [.new, .old], context: nil)     lab2.addObserver(self, forKeyPath: "frame", options: .new, context: nil)         override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {     if lab1.isEqual(object){         print("lab1 改变")         if keyPath == "text"{             print("lab1 text改变")             if let old = change?[NSKeyValueChangeKey.oldKey] {                 print("old = \(old)") //               }                                     if let new = change?[NSKeyValueChangeKey.newKey] {                 print("new = \(new)") // Albert               }         }else{             print("lab1 frame 改变")             if let old = change?[NSKeyValueChangeKey.oldKey] {                 print("old = \(old)") //               }                                     if let new = change?[NSKeyValueChangeKey.newKey] {                 print("new = \(new)") // Albert               }         }     }else{                   print("lab2 改变")         if keyPath == "text"{             print("lab2 text改变")         }else{             print("lab2 frame 改变")         }     } }       deinit {     lab1.removeObserver(self, forKeyPath: "text")     lab1.removeObserver(self, forKeyPath: "frame")     lab2.removeObserver(self, forKeyPath: "text")     lab2.removeObserver(self, forKeyPath: "frame") }