无法转换'UILabel'类型的值！预期参数'type inout String' [英] cannot convert value of type 'UILabel!' to expected argument 'type inout String'

问题描述

当我尝试增加 currentNumberAdmin 时，我得到：

When I try to increase currentNumberAdmin I get:

无法转换价值类型'UILabel！'到期望参数'输入字符串'

cannot convert value of type 'UILabel!' to expected argument 'type in out String'

class adminPanel: UIViewController {

    @IBOutlet weak var currentNumberAdmin: UILabel!                       

    @IBAction func nextCurrent(_ sender: UIButton) {
        let database = FIRDatabase.database().reference()
        database.child("current").observe(FIRDataEventType.value, with: { (snapshot) in

          self.currentNumberAdmin.text = snapshot.value as! String
          currentNumberAdmin += String(1)
        })

    }
}

有谁知道如何转换和增加 currentNumberAdmin 是否正确？

Does anyone know how I can convert and increase currentNumberAdmin correctly?

推荐答案

由于这一行而崩溃： currentNumberAdmin + = String（1）。您正在尝试将字符串值添加到UILabel值，该值无效。你实际上告诉编译器将 currentNumberAdmin （一个UILabel）分配给将一个UILabel添加到String的表达式的值，编译器不知道如何do，因此是异常消息。

This is crashing because of this line: currentNumberAdmin += String(1). You're attempting to add a String value to a UILabel value, which is invalid. You're literally telling the compiler to assign currentNumberAdmin, a UILabel, to the value of the expression of adding a UILabel to a String, which the compiler doesn't know how to do, hence the exception message.

为什么你试图设置标签的文本两次并不完全清楚：一次使用snapshot.value，然后再次使用线。如果您要做的是将标签的文本设置为快照值+ 1，请执行以下操作：

It's not entirely clear why you're attempt to set the label's text twice: once with snapshot.value, and then again on the next line. If what you're trying to do is set the label's text to the snapshot value + 1, do something like this:

@IBAction func nextCurrent(_ sender: UIButton) {
    let database = FIRDatabase.database().reference()
    database.child("current").observe(FIRDataEventType.value, with: { (snapshot) in

      var strVal = Int(self.currentNumberAdmin.text)!
      strVal += 1
      self.currentNumberAdmin.text = String(strVal)
    })

}

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