Undeclared type "PlaylistDetailViewController"

import UIKit

class PlaylistMasterViewController: UIViewController {

    @IBOutlet weak var aButton: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()

        aButton.setTitle("Press me!", forState: .Normal)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "showPlaylistDetail" {
            let playlistDetailController = segue.destinationViewController as! PlaylistDetailViewController   // error said: Undeclared type "PlaylistDetailViewController"
            playlistDetailController.buttonPressLabel.text = "Yay! You Pressed the button"
        }
    }
}



import UIKit

class PlaylistDetailViewController: UIViewController {

    @IBOutlet weak var buttonPressLabel: UILabel!

    var segueLabelText: String = ""

    override func viewDidLoad() {
        super.viewDidLoad()

        buttonPressLabel.text = segueLabelText
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}