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Question

我有用于在应用程序中运行历史记录的代码。

如何改进它，以便在按下时立即显示数字，而不仅仅是按 =？

我的程序:

 // Connected to button "="
@IBAction func equalitySignPressed(sender: UIButton) {
  if stillTyping {
     secondOperand = currentInput
  }
dotIsPlaced = false

addHistory(text: operationSign + displayResultLabel.text!)

switch operationSign {
   case "+":
      operateWithTwoOperands{$0 + $1}
   case "-":
      operateWithTwoOperands{$0 - $1}
   case "×":
      operateWithTwoOperands{$0 * $1}
   case "÷":
      operateWithTwoOperands{$0 / $1}
default: break
  }
}
func addHistory(text: String){
     //Add text
    resultLabelText.text =  resultLabelText.text! + "" + text
}

当前输出:

Answer 1

您可以在此处使用键值观察(KVO)。

addObserver(self, forKeyPath: #keyPath(INPUTS), options: [.old, .new], context: nil)

您可以将值观察为

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if keyPath == #keyPath(INPUT) {
        // Update UI
        resultLabelText = "NEW_VALUE"
    }
}