在两个ViewControllers（委托）之间传递数据 - Swift [英] Passing data between two ViewControllers (delegate) - Swift

问题描述

我有两个 ViewController's。

1. FirstVC - 我有标签和按钮 with seguemodal

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

SecondVC - 我有 PickerView 和按钮（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 中创建了委托作为：

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 的功能，在这个函数中，我使用我的委托：

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
     }
 }

请帮我解决这个问题。

推荐答案

1）你需要将委托设置为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）将委托设为可选

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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