ios - 通过 segue 发送的任何内容都返回 nil

Question

下面是我的 segue 代码，但是当我尝试在另一个 View Controller 中访问它们时，所有变量都返回 nil。我什至添加了一个简单的字符串值来发送，它也返回 nil。

extension ViewController : MPMediaPickerControllerDelegate {
// must implement these, as there is no automatic dismissal

func mediaPicker(mediaPicker: MPMediaPickerController!, didPickMediaItems mediaItemCollection: MPMediaItemCollection!) {

    let ViewControllerhost:ViewControllerHost = storyboard?.instantiateViewControllerWithIdentifier("HostViewController") as! ViewControllerHost

    let representativeItem = mediaItemCollection.representativeItem
    let title = representativeItem.title
    let artistName = representativeItem.artist

    segueInfo =
        [ "representativeItem": representativeItem
            , "title": title
            , "artistName": artistName ]

    var albumCover  = "\(MPMediaItemArtwork())"
    var songInfo = "\(MPMediaItem())"
    var messageDict = [albumCover, songInfo]

    //This sends across Album Artwork, Info, and the duration is sent from the Host view controller
    let messageData = NSJSONSerialization.dataWithJSONObject(messageDict, options: NSJSONWritingOptions.PrettyPrinted, error: nil)

    var error:NSError?

    appDelegate.mpcHandler.session.sendData(messageData, toPeers: appDelegate.mpcHandler.session.connectedPeers, withMode: MCSessionSendDataMode.Unreliable, error: &error)

    if error != nil{
        println("error: \(error?.localizedDescription)")
    }

     func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

        if let nextVC = segue.destinationViewController as? ViewControllerHost
            , let sender = sender as? ViewController {
                /*nextVC.representativeItem_ = sender.segueInfo["representativeItem"] as? MPMediaItem
                nextVC.title_ = sender.segueInfo["title"] as! String
                nextVC.artistName_ = sender.segueInfo["artistName"] as! String*/
                nextVC.representativeItem_ = representativeItem
                nextVC.title_ = title
                nextVC.artistName_ = artistName
                nextVC.test_ = test
        }
    }

    dismissViewControllerAnimated(true, completion: {
        self.navigationController?.pushViewController(ViewControllerhost, animated: true)
    })
}








func mediaPickerDidCancel(mediaPicker: MPMediaPickerController!) {
    self.dismissViewControllerAnimated(true, completion: nil)

}

Answer 1

我怀疑这个条件失败了:

if let nextVC = segue.destinationViewController as? ViewControllerHost, let sender = sender as? ViewController {

具体来说，if let sender = sender as? ViewController { 部分。

根据docs , sender 是触发 segue 的按钮或 View 。它不是 View Controller 本身，所以 if let sender = sender as? ViewController { 可能返回 false。