一种简单的控制播放器控制的方法

Player.swift

/// Queue player
struct Player {
    /// The player status
    ///
    /// - idle: before play
    /// - waiting: means it is waiting for loading asset
    /// - playing: now playing
    /// - paused: paused
    /// - stopped: end play
    enum Status {
        case idl
        case waiting
        case playing
        case paused
        case stopped
    }

    enum Flag {
        /// keyboard showing
        case keyboard
        /// app inactive
        case inactive
        /// view disappear
        case disappear
        /// user action
        case action
        /// picker showing
        case picker
        /// holding
        case holding
        /// fetching data
        case fetching
        /// exporting asset (id)
        case exporting(String)
    }

    struct Barrier {
        /// all flags
        var flags: Set<Flag> = []

        /// current supported flags
        static let enabledFlags: Set<Flag> = [.keyboard, .inactive, .disappear, .action, .picker, .holding]
    }

    /// player barrier
    private var barrier = Barrier()

    /// player status
    private var status: Status = .idle

    /// current index
    private var currentIndex: Int
}

extension Player.Flag: Hashable {
}

extension Player {

    /// Player try to become active with flag
    ///
    /// - Parameter flag: leave flag
    func becomeActive(flag: Flag) {
        barrier.flags.remove(flag)

        guard Barrier.enabledFlags.intersection(barrier.flags).isEmpty else {
            return
        }

        switch status {
        case .paused:
            resume()
        case .idle, .waiting, .stopped:
            tryPlay(at: currentIndex)
        case .playing:
            break
        }
    }

    /// Player resign active with flag
    ///
    /// - Parameter flag: enter flag
    func resignActive(flag: Flag) {
        barrier.flags.insert(flag)

        switch status {
        case .playing:
            pause()
        default:
            break
        }
    }

    /// Add a flag，without update status (enter)
    ///
    /// - Parameter flag: the flag
    func add(flag: Flag) {
        barrier.flags.insert(flag)
    }

    /// Remove a flag，without update status (leave)
    ///
    /// - Parameter flag: the flag
    func remove(flag: Flag) {
        barrier.flags.remove(flag)
    }

    // MAKR: play control

    private func tryPlay(at index: Int) {
        ...
        play()
    }

    private func play() {
    }

    private func pause() {
    }

    private func resume() {
    }

    private func stop() {
    }
}