问题描述

我有两个 ViewController.

1. FirstVC - 我有 label 和 button 与 segue "modal"

1. FirstVC - I have label and button with segue "modal"

SecondVC - 我有 PickerView 和 button(返回 FirstVC):

SecondVC - I have PickerView and button (back to FirstVC):

@IBAction func bntback(sender: AnyObject) {
          self.dissmissViewControllerAnimatied(true, completion: nil)
    }

我在 SecondViewController 中创建了委托:

And I created delegate in SecondViewController as:

protocol SendDataDelegate {
   func sendData(text:String)
}

下一步:

class SecondVC: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate {
      var delegate: SendDataDelegate!
      var firstvc = FirstVC()
      var arr = ["First", "Second", "Third"]
      @IBOutlet var pickview: UIPickerView!
      override func viewDidLoad() {
         super.viewDidLoad()
         pickview.dataSource = self
         pickview.selegate = self
     }

我的 PickerView 函数，在这个函数中我使用我的委托作为:

My function of PickerView and in this function I use my delegate as:

func pickerView (pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
  var text = arr[row]
  dispatch_async(dispatch_get_main_quene(), {
  self.delegate.sendData(text)//there is an error: "fatal error: unexpectedly found nil while unwrapping an Optional value"
  )}
}

第一VC:

class FirstVC: UIViewController, SendDataDelegate {
      var data = SecondVC()
      //....
      override func viewDidLoad() {
         super.viewDidLoad()
         self.data.delegate = self
     }
     func sendData (text:String) {
        mylable.text = text
        //or 
        //var txt = text
       //mylable.text = txt
     }
 }

请帮我解决这个问题.

推荐答案

1) 你需要将delegate设置成prepareForSegue:

1) You need to set delegate into prepareForSegue:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if let viewController = segue.destinationViewController as? SecondVC {
        viewController.delegate = self
    }
}

更新:

2) 将 delegate 设置为可选

2) Set delegate as Optional

class SecondVC: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate {
    var delegate: SendDataDelegate?
    ...

    func pickerView (pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        var text = arr[row]
        dispatch_async(dispatch_get_main_quene(), {
            self.delegate?.sendData(text)
        )}
    }

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