Passing data between two ViewControllers (delegate

问题:

This question already has an answer here:

• Passing Data between View Controllers 40 answers

I have two ViewController's.

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

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

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

And I created delegate in SecondViewController as:

protocol SendDataDelegate {
   func sendData(text:String)
}

Next:

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
     }

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"
  )}
}

FirstVC:

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
     }
 }

Help me please with this problem.

回答1:

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
    }
}

UPDATE:

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)
        )}
    }