BaseController 委托在选项卡栏控制器内的所有继承视图控制器中不起作用

Question

我很难理解为什么我在基本控制器中定义的委托不能在继承的视图控制器中工作。

我有一个 TabBarController，它有 2 个 ViewController。每个 ViewController 都是 BaseController 的子类。

BaseController 实现一个委托并更新一个标签视图。

当我启动应用程序并单击播放时，FirstVC 会更新标签，但是当我将选项卡切换到 SecondVC 时，它会开始更新，但是当我再次单击 FirstVC 时，更新卡住并且不会更新标签，但标签会不断更新在 SecondVC 中。

import Foundation
import AVFoundation

protocol SharedPlayerNotificaions : class {

    func willPlay(status: Bool)
    func currentPlayTime(timeString: String)
}

class SharedPlayer : NSObject {

    static let sharedInstance = SharedPlayer()    
    private var player : AVPlayer?
    weak var delegate : SharedPlayerNotificaions?

    override private init() {
        super.init()
        player = AVPlayer()

    }

    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
        if keyPath == "status" {

            if player?.status == AVPlayerStatus.Unknown {
                delegate?.willPlay(false)
            }
            if player?.status == AVPlayerStatus.Failed {
                print("failed")
                delegate?.willPlay(false)
            }

            if player?.status == AVPlayerStatus.ReadyToPlay {
                print("readytoplay")
                delegate?.willPlay(true)
            }
        }
        if keyPath == "rate" {
        }
        if keyPath == "duration" {   
        }
    }

    func play(){

        player?.play()
        let interval = CMTime(value: 1, timescale: 2)
        player?.addPeriodicTimeObserverForInterval(interval, queue: dispatch_get_main_queue(), usingBlock: { (progressTime) in
            let seconds = CMTimeGetSeconds(progressTime)
            let secondsString = String(format: "%02d", Int(seconds % 60))
            let minutesString = String(format: "%02d", Int(seconds / 60))
            self.delegate?.currentPlayTime("\(minutesString):\(secondsString)")
        })
    }

    func setUrl(urlString: String){

        if let url = NSURL(string: urlString){
            player = AVPlayer(URL: url)
            player?.addObserver(self, forKeyPath: "status", options: NSKeyValueObservingOptions.New, context: nil)
             player?.addObserver(self, forKeyPath: "rate", options: NSKeyValueObservingOptions.New, context: nil)
             player?.addObserver(self, forKeyPath: "duration", options: NSKeyValueObservingOptions.New, context: nil)
        }
    }
}

基础控制器

    class BaseController : UIViewController, SharedPlayerNotificaions {

        let label = UILabel()

        override func viewDidLoad() {

            SharedPlayer.sharedInstance.delegate = self

            view.addSubview(label)
            label.translatesAutoresizingMaskIntoConstraints = false
            view.addConstraint(NSLayoutConstraint(item: label, attribute: .Left, relatedBy: .Equal, toItem: view, attribute: .Left, multiplier: 1, constant: 10))
            view.addConstraint(NSLayoutConstraint(item: label, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 50))
            view.addConstraint(NSLayoutConstraint(item: label, attribute: .Top, relatedBy: .Equal, toItem: view, attribute: .Top, multiplier: 1, constant: 10))

            label.text = "00:00"
        }


   func currentPlayTime(timeString: String) { 
    dispatch_async(dispatch_get_main_queue()) { 
        self.label.text = timeString
    }
}

        func willPlay(status: Bool) {

        }
}

FirstViewController

class FirstViewController: BaseController {


    @IBAction func playButton(sender: AnyObject) {

        let urlString = "https://someStreamUrl"

        SharedPlayer.sharedInstance.setUrl(urlString)
        SharedPlayer.sharedInstance.play()

      }

}

第二视图控制器

class SecondViewController : BaseController {

    override func viewDidLoad() {

        super.viewDidLoad()
        view.backgroundColor = .redColor()
    } 
}

Answer 1

主要缺陷是SharedPlayer 是单例。只有一个实例。它只能有一个代表。但是您创建了两个视图控制器。两者都试图告诉单个共享 SharedPlayer 实例它是委托。第二个获胜。

委托模式仅在有一个委托时有效。在这种情况下，您有两个，因此您不能使用传统的委托模式。

有几种可能的解决方案。

1. 更新 SharedPlayer 以接受委托数组而不是单个委托。
2. 使用NSNotificationCenter。让SharedPlayer 发布通知，并让每个视图控制器注册每个可能的通知。