Array Select First Data on Picker Swift

Question

Resistor array 1 array 3 array IM, and I'm in this to collect. I want to draw the first element of this array. But when I do this, I get an error in practice. How do I get the first data in the picker in the textfield? I want to print textfield to the first data in the picker. The code does not work with this state.

I get an error in this line of code:

 getDevice.text = gradePickerValues[0]

     override func viewDidLoad() {
            super.viewDidLoad()
GetDevice()
    getDevice.text = gradePickerValues[0]
    }

      var picker = UIPickerView()

        var gradePickerValues1 = [String]()
        var gradePickerValues2 = [String]()
        var gradePickerValues3 = [String]()
        var gradePickerValues = [String]()

        let multiplearray = DispatchGroup()


        @objc func GetDevice() {


            if !chipnumber.text!.isEmpty {
                 multiplearray.enter()

                let ref = Database.database().reference().child(chipnumber.text!).child("titles").child("0").child("DeviceName")

                ref.observeSingleEvent(of: .value, with: { (snapshot) in
                    //let value: NSDictionary = snapshot.value as! NSDictionary
                    let dic = snapshot.value as! String
                    self.gradePickerValues1 = [dic]
                    self.multiplearray.leave()
                })

            }

            if !chipnumber2.text!.isEmpty {
                multiplearray.enter()

                let ref = Database.database().reference().child(chipnumber2.text!).child("titles").child("0").child("DeviceName")

                ref.observeSingleEvent(of: .value, with: { (snapshot) in
                    //let value: NSDictionary = snapshot.value as! NSDictionary
                    let dic = snapshot.value as! String
                    self.gradePickerValues2 = [dic]
                    self.multiplearray.leave()
                })

            }

            if !chipnumber3.text!.isEmpty {
                multiplearray.enter()

                let ref = Database.database().reference().child(chipnumber3.text!).child("titles").child("0").child("DeviceName")

                ref.observeSingleEvent(of: .value, with: { (snapshot) in

                    let dic = snapshot.value as! String
                    self.gradePickerValues3 = [dic]
                    self.multiplearray.leave()
                })

            }

            multiplearray.notify(queue:.main) {

                self.gradePickerValues = self.gradePickerValues1 + self.gradePickerValues2 + self.gradePickerValues3

            }
        }

        func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int){
            getDevice.text = gradePickerValues[row]

            switch row {
            case 0:
                    fetchDevies()

            case 1:
                    fetchdevieschip2()

            case 2:
                    fetchdevieschip3()

            default: break

            }
            self.view.endEditing(true)
        }

Answer 1

GetDevice() contains asynchronous tasks. Update the label in the notify closure after populating the array.

And please name functions/methods with starting lowercase letter.

override func viewDidLoad() {
   super.viewDidLoad()
   getDevice()
} 

...

@objc func getDevice() {

...

   multiplearray.notify(queue:.main) {
      self.gradePickerValues = self.gradePickerValues1 + self.gradePickerValues2 + self.gradePickerValues3
      getDevice.text = gradePickerValues[0]
   }