"仅观察使用 KVO 所做的更改"

Question

我有一个 AVPlayer 对象，我正在使用 KVO 观察状态变化； 对 .timeControlStatus 的更改，它告诉您 AVPlayer 是在播放、停止、加载还是暂停。

问题是 AVPlayer 在文件加载时多次将 .timeControlStatus 属性设置为 .waitingToPlayAtSpecifiedRate （表示文件正在加载）。 我只想在第一次<\/strong>加载更改时收到通知，而不是后续设置。 我的观察者是这样设置的：

// watch .timeControlStatus
    playerStatusToken = player?.observe(\.timeControlStatus, options: [.new], changeHandler: { [weak self] player, change in
        if player.timeControlStatus == AVPlayer.TimeControlStatus.paused {
            if self?.playerItemActive == false {
                print("playback stopped")
                self?.prevID = self!.currentID
                self?.currentID = 0
                self?.currentURL = nil
                self?.playState = .stopped
            }
            else {
                print("playback paused")
                self?.playState = .paused
            }
        }
        else if player.timeControlStatus == AVPlayer.TimeControlStatus.playing {
            self?.playState = .playing
        }
        else if player.timeControlStatus == AVPlayer.TimeControlStatus.waitingToPlayAtSpecifiedRate {
            self?.playState = .loading
        }
    })

Answer 1

使用Combine<\/code>允许您观察变化并过滤掉重复值开箱即用

// retain var in your class
var cancellable: Cancellable?


// observe changes
cancellable = player?.publisher(for: \.timeControlStatus)
    .removeDuplicates()
    .sink() { 
        // your change handler 
    }