cannot convert value of type 'UILabel!' to expected argument '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\'

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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)
    })

}