FootPrints

//占位符(切入3号位):text控件名.placeholder = ""(不聚焦) testField.placeholder = "please enter the user name"

//弹出提示框(切入2号位) @IBAction func register(_ sender: AnyObject) {                           //关联有效控件   if(username.text = "") {       let alertController = UIAlertController(title: "系统提示", message: "请输入用户名", preferredStyle: UIAlertController.alert)       let cancelAction = UIAlertAction(title: "取消", style: UIAlertActionStyle.cancel, handler: nil)       let okAction = UIAlerAction(title: "确定",style: UIAlertActionStyle.default, handler: nil) alertController.addAction(cancelAction) alertController.addAction(okAction) self.present(alertController, animated: true, completion: nil)              } }

//限制文本框字数  //切入class UITextFieldDelegate  //切入3号位  text.delegate = self //切入4号位 @objc func handleTap(sender: UITapGestureRecognizer) { if