在做voip通话的过程中，会频繁使用到免提播放和听筒接听的功能，而如何正确的切换，和AudioManager的调度是分不开的，直接上代码：

//获取AudioManager服务
private val audioManager =
    AppUtils.getApplication().getSystemService(Context.AUDIO_SERVICE) as AudioManager

/**
 * 扬声器切换
 * true: 打开
 */
fun setSpeakerPhoneOn(on: Boolean) {
    if (on) {
        //设置mode 
        audioManager.mode = AudioManager.MODE_IN_COMMUNICATION
        //设置音量，解决有些机型切换后没声音或者声音突然变大的问题
        audioManager.setStreamVolume(
            AudioManager.STREAM_VOICE_CALL,
            audioManager.getStreamVolume(AudioManager.STREAM_VOICE_CALL),
            AudioManager.FX_KEY_CLICK
        )
        //扬声器开启，此方法调用之前需要先设置好mode
        audioManager.isSpeakerphoneOn = true
    } else {
        //5.0以上
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            //设置mode 
            audioManager.mode = AudioManager.MODE_IN_COMMUNICATION
            //设置音量，解决有些机型切换后没声音或者声音突然变大的问题
            audioManager.setStreamVolume(
                AudioManager.STREAM_VOICE_CALL,
                audioManager.getStreamVolume(AudioManager.STREAM_VOICE_CALL),
                AudioManager.FX_KEY_CLICK
            )
        } else {
            //设置mode 
            audioManager.mode = AudioManager.MODE_IN_CALL
            audioManager.setStreamVolume(
                AudioManager.STREAM_VOICE_CALL,
                audioManager.getStreamVolume(AudioManager.STREAM_VOICE_CALL),
                AudioManager.FX_KEY_CLICK
            )
        }
        //扬声器关闭，此方法调用之前需要先设置好mode
        audioManager.isSpeakerphoneOn = false
    }
}

/**
 * 麦克风开关
 * RINGER_MODE_SILENT 静音,且无振动
 * RINGER_MODE_VIBRATE 静音,但有振动
 * RINGER_MODE_NORMAL 正常声音,振动开关由setVibrateSetting决定.
 * true:静音
 */
fun setVoiceOn(on: Boolean) {
    audioManager.isMicrophoneMute = on
//    ToastUtils.shortBottom(if (on) "麦克风已关闭" else "麦克风已启用")
}

/**
 * 重设audioManager状态
 * 扬声器切换为NORMAL && 打开麦克风
 */
fun resetAudioState() {
    //设置mode 为喇叭播放
    audioManager.mode = AudioManager.MODE_NORMAL
    //设置音量，解决有些机型切换后没声音或者声音突然变大的问题
    audioManager.setStreamVolume(
        AudioManager.STREAM_MUSIC,
        audioManager.getStreamVolume(AudioManager.STREAM_MUSIC),
        AudioManager.FX_KEY_CLICK
    )
    audioManager.isSpeakerphoneOn = true

    setVoiceOn(false)
}

方法调用代码如上，下面来分析一下使用中要重点注意的元素：
1.audioManager.mode
AudioManager中给出了如下mode种类，正确的选择mode进行配置，才能提升用户体验；

/**
     * Invalid audio mode.
     */
    public static final int MODE_INVALID            = AudioSystem.MODE_INVALID;
    /**
     * Current audio mode. Used to apply audio routing to current mode.
     */
    public static final int MODE_CURRENT            = AudioSystem.MODE_CURRENT;
    /**
     * Normal audio mode: not ringing and no call established.
     */
    public static final int MODE_NORMAL             = AudioSystem.MODE_NORMAL;
    /**
     * Ringing audio mode. An incoming is being signaled.
     */
    public static final int MODE_RINGTONE           = AudioSystem.MODE_RINGTONE;
    /**
     * In call audio mode. A telephony call is established.
     */
    public static final int MODE_IN_CALL            = AudioSystem.MODE_IN_CALL;
    /**
     * In communication audio mode. An audio/video chat or VoIP call is established.
     */
    public static final int MODE_IN_COMMUNICATION   = AudioSystem.MODE_IN_COMMUNICATION;

在VOIP场景中，主要就是为了通话服务，所以选择mode的时候，设置为MODE_IN_COMMUNICATION 就比较合适，如果设置为MODE_NORMAL 去开启扬声器，就可能会出现和其他音频播放声音混杂，甚至互相干扰啸叫严重的问题。