Swift performSegueWithIdentifier shows black scree

问题:

I have read through a lot of different posts regarding this issue, but none of the solutions seemed to work for me.

I started a new app and I placed the initial ViewController inside a navigation controller. I created a second view and linked them together on the storyboard with a segue. The segue works successfully, and I can see the data I am transferring in a print statement from the second screen, but the screen shows black.

WelcomeScreen:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "segueToTraits"{
        if let gender = self.selectedGender{
            let traitVC = segue.destinationViewController as? TraitViewController
            traitVC!.gender = gender
        }
    }
}

func sendGenderToTraitsView(gender : String?){
    performSegueWithIdentifier("segueToTraits", sender: self)

}

@IBAction func button1(sender: UIButton) {
    selectedGender = boyGender
    self.sendGenderToTraitsView(selectedGender)
}


@IBAction func button2(sender: UIButton) {
    selectedGender = girlGender
    self.sendGenderToTraitsView(selectedGender)
}

Storyboard: Link to image of my storyboard My segue is set as follows: Link to image of my segue information

Also, my viewControllers are named WelcomeViewController and TraitViewController. They have storyboard id's of welcomeVC and traitsVC.

Any help would be incredibly appreciated. Let me know if you need any other information.

回答1:

I've build your app and everything works, maybe you've missed something, here is my solution (Note: Code is in Swift 3.0, but should be easy to adopt it to Swift 2.*):

The storyboard:

Set the segueToTraits identifier:

Set the TraitViewController class as custom class in the storyboard:

The view controller with the buttons:

import UIKit

class ViewController: UIViewController {  

  let boyGender = "boy"
  let girlGender = "girl"
  var selectedGender: String?


  override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "segueToTraits"{
      if let gender = self.selectedGender {
        let traitVC = segue.destination as? TraitViewController
        traitVC!.gender = gender
      }
    }
  }

  func sendGenderToTraitsView(gender : String?){
    performSegue(withIdentifier: "segueToTraits", sender: self)

  }

  @IBAction func button1(sender: UIButton) {
    selectedGender = boyGender
    self.sendGenderToTraitsView(gender: selectedGender)
  }


  @IBAction func button2(sender: UIButton) {
    selectedGender = girlGender
    self.sendGenderToTraitsView(gender: selectedGender)
  }

}

The trait view controller:

import UIKit

class TraitViewController: UIViewController {


  var gender: String = ""

  override func viewDidLoad() {
    super.viewDidLoad()

    print("gender: \(gender)")
  }

}

Result:

You can find the sample project here

回答2:

By following the steps that @ronatory had laid out so well for me in the accepted answer, I was able to see that I had set up my TraitViewController as a UIPageViewController instead of UIViewController.. and so it didn't generate any errors, but it just took me to a black screen. Feel silly that I read through my code so many times and never noticed this.

Main point: If you're getting a black screen on a ViewController randomly, make sure your class is extending the correct parent class. in my case:

class TraitViewController: UIPageViewController {

needed to be

class TraitViewController: UIViewController {