有时我们需要在IOS程序中，监听音量按下的动作，可以用下面的方法。

• 在后台模式中，打开Audio开关

只有打开这个开关，才能在锁屏模式下，监听到音量按钮

---

• SceneDelegate.swift 代码

import UIKit
import SwiftUI
import AudioToolbox


class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).

        // Create the SwiftUI view that provides the window contents.
        let contentView = ContentView()

        // Use a UIHostingController as window root view controller.
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: contentView)
            self.window = window
            window.makeKeyAndVisible()
        }

        // 这里面监听音量按钮
        NotificationCenter.default.addObserver(self, selector: #selector(self.changeVolumSlider), name: NSNotification.Name(rawValue: "AVSystemController_SystemVolumeDidChangeNotification"), object: nil)
        UIApplication.shared.beginReceivingRemoteControlEvents()
}
    
   // 当音量按钮按下时，会触发下面的方法
    @objc func changeVolumSlider(notifi: NSNotification) {
        
        let reason = (notifi.userInfo?["AVSystemController_AudioVolumeChangeReasonNotificationParameter"] as? String) ?? ""
        if reason == "ExplicitVolumeChange" {
            for checkPointInfo in checkPointInfoCommonList where checkPointInfo.noticeStatus == .fire {
                checkPointInfo.noticeStatus = .stop
                checkPointInfo.stopAlert()
            }
        }
    }

func sceneDidDisconnect(_ scene: UIScene) {
    // Called as the scene is being released by the system.
    // This occurs shortly after the scene enters the background, or when its session is discarded.
    // Release any resources associated with this scene that can be re-created the next time the scene connects.
    // The scene may re-connect later, as its session was not necessarily discarded (see `application:didDiscardSceneSessions` instead).
}

func sceneDidBecomeActive(_ scene: UIScene) {
    // Called when the scene has moved from an inactive state to an active state.
    // Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
}

func sceneWillResignActive(_ scene: UIScene) {
    // Called when the scene will move from an active state to an inactive state.
    // This may occur due to temporary interruptions (ex. an incoming phone call).
}

func sceneWillEnterForeground(_ scene: UIScene) {
    // Called as the scene transitions from the background to the foreground.
    // Use this method to undo the changes made on entering the background.
}

func sceneDidEnterBackground(_ scene: UIScene) {
    // Called as the scene transitions from the foreground to the background.
    // Use this method to save data, release shared resources, and store enough scene-specific state information
    // to restore the scene back to its current state.
}

}

• 需要特别注意，只有在音频文件播放时，才能在锁屏状态下控制音量。可以录制一个音频文件，循环播放。

AudioPlayer

import Foundation
import AVFoundation

class AudioPlayer: NSObject, AVAudioPlayerDelegate {
    
    static let instance = AudioPlayer()
    
    static var audioPlayer: AVAudioPlayer = {
        return AVAudioPlayer()
    }()

    func initAudioPlayer(songTitle: String) {

        let songTitle = songTitle
        let path = Bundle.main.path(forResource: songTitle, ofType: nil, inDirectory: "music")!
        let url = URL(fileURLWithPath: path)
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSession.Category.playback)
            AudioPlayer.audioPlayer = try AVAudioPlayer(contentsOf: url)
            AudioPlayer.audioPlayer.delegate = self
        } catch {

        }
    }

    func stop() {
        AudioPlayer.audioPlayer.stop()
    }

    func pause() {
        AudioPlayer.audioPlayer.pause()
    }
    
    func play() {
        AudioPlayer.audioPlayer.play()
    }
    
    func currentTime() -> Int {
        return Int(AudioPlayer.audioPlayer.currentTime)
    }
    
    func getTotalTime() -> Int {
        return Int(AudioPlayer.audioPlayer.duration)
    }
    
    func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool) {
    }
}



AudioPlayer.instance.initAudioPlayer(songTitle: "notice.mp3")
AudioPlayer.instance.play()