AudioServicesPlaySystemSound音量依赖

Question

我正在进行iOS键盘扩展。

要播放点击声，我使用AudioServicesPlaySystemSound。

然而有些用户报告说，咔嗒声有时取决于铃声音量（铃声图标）＆＃39;有时＆＃39;正常的音量（扬声器图标）＆＃39;

我在Apple备忘录应用程序上进行了测试，发现存在关于不稳定依赖的案例。

这是我的init

代码

func initTypeSound(soundIndex: Int) {
    let bundle = NSBundle.mainBundle()
    for var i = 0 ; i < MAX_TYPE_SOUND_COUNT ; i++ {
        if let url = bundle.URLForResource(NSString(format: "type%d_%d", soundIndex, i) as String, withExtension: "wav") {
            // file exist
            var soundID : SystemSoundID = 0
            AudioServicesCreateSystemSoundID(url, &soundID)
            mTypeSoundIDs.insert(soundID, atIndex: i)
        } else {
            // no file
        }
    }
}

和要播放的代码

func play(soundType: KKSoundType) {
    if (!mHasPermission || !mIsSound) {
        return
    }

    var session = AVAudioSession.sharedInstance()
    let systemVolumn = session.outputVolume
    if (systemVolumn == 0) {
        return
    }

    var soundId : SystemSoundID!
    switch (soundType) {
    case .Type:
        let rand = Int(arc4random_uniform(UInt32(mTypeSoundIDs.count)));
        soundId = mTypeSoundIDs[rand];
        break
    case .Space:
        soundId = mSpaceSoundID;
        break
    default:
        return
    }
    if mIsSound {
        AudioServicesPlaySystemSound(soundId)
    }
}