无法转换'UILabel！'类型的值！ 预期参数'type inout String'

Question

When I try to increase currentNumberAdmin I get:

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)
        })

    }
}

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

Answer 1

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.

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)
    })

}