Android中通过耳机按键控制音乐播放的实现

今天在研究Android中实现Android 4.2.2源码中的Music应用的源码，关于通过耳机按键控制音乐播放的实现，有点好奇，就仔细分析了一下源码，

主要由MediaButtonIntentReceiver 这个类来实现。

在AndroidManifest.xml中有如下Receiver的注册：

        <receiver android:name="com.huawei.imax.music.MediaButtonIntentReceiver" >            <intent-filter>                <action android:name="android.intent.action.MEDIA_BUTTON" />                <action android:name="android.media.AUDIO_BECOMING_NOISY" />            </intent-filter>        </receiver>

其实关键是对这两个ACTION的监控：

android.intent.action.MEDIA_BUTTON的说明如下，从注释看，就是媒体按键被按下后，通过Intent.EXTRA_KEY_EVENT 中带上触发此事件的具体按钮事件：

   /**     * Broadcast Action:  The "Media Button" was pressed.  Includes a single     * extra field, {@link #EXTRA_KEY_EVENT}, containing the key event that     * caused the broadcast.     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String ACTION_MEDIA_BUTTON = "android.intent.action.MEDIA_BUTTON";

android.intent.action.AUDIO_BECOMING_NOISY的说明如下（自己翻译的，大概这个意思），

从注释看，当音频变得“吵闹”，比如耳机拔出，或者A2DP音频通道（比如通过蓝牙音箱播放音乐就是一种A2DP的应用场景）断开，

音频系统将会自动将音频转到自带的扬声器。收到此intent的控制音频的应用可以暂停，降低音量或其它操作，以防扬声器突然发出声音让用户受惊：

    /**     * Broadcast intent, a hint for applications that audio is about to become     * 'noisy' due to a change in audio outputs. For example, this intent may     * be sent when a wired headset is unplugged, or when an A2DP audio     * sink is disconnected, and the audio system is about to automatically     * switch audio route to the speaker. Applications that are controlling     * audio streams may consider pausing, reducing volume or some other action     * on receipt of this intent so as not to surprise the user with audio     * from the speaker.     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String ACTION_AUDIO_BECOMING_NOISY = "android.media.AUDIO_BECOMING_NOISY";

MediaButtonIntentReceiver 的关键实现如下：

public class MediaButtonIntentReceiver extends BroadcastReceiver{    ...        @Override    public void onReceive(Context context, Intent intent)    {        String intentAction = intent.getAction();        if (AudioManager.ACTION_AUDIO_BECOMING_NOISY.equals(intentAction))        {            Intent i = new Intent(context, MediaPlaybackService.class);            i.setAction(MediaPlaybackService.SERVICECMD);            i.putExtra(MediaPlaybackService.CMDNAME,                    MediaPlaybackService.CMDPAUSE);            context.startService(i);        }        else if (Intent.ACTION_MEDIA_BUTTON.equals(intentAction))        {            KeyEvent event = (KeyEvent) intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);                        if (event == null)            {                return;            }                        int keycode = event.getKeyCode();            int action = event.getAction();            long eventtime = event.getEventTime();                        // single quick press: pause/resume.             // double press: next track            // long press: start auto-shuffle mode.                        String command = null;            switch (keycode)            {                case KeyEvent.KEYCODE_MEDIA_STOP:                    command = MediaPlaybackService.CMDSTOP;                    break;                case KeyEvent.KEYCODE_HEADSETHOOK:                case KeyEvent.KEYCODE_MEDIA_PLAY_PAUSE:                    command = MediaPlaybackService.CMDTOGGLEPAUSE;                    break;                case KeyEvent.KEYCODE_MEDIA_NEXT:                    command = MediaPlaybackService.CMDNEXT;                    break;                case KeyEvent.KEYCODE_MEDIA_PREVIOUS:                    command = MediaPlaybackService.CMDPREVIOUS;                    break;                case KeyEvent.KEYCODE_MEDIA_PAUSE:                    command = MediaPlaybackService.CMDPAUSE;                    break;                case KeyEvent.KEYCODE_MEDIA_PLAY:                    command = MediaPlaybackService.CMDPLAY;                    break;            }

通过接收此事件的广播，想进行什么操作，完全看你的业务需求了。

一开始以为耳机插拔，是通过ACTION_HEADSET_PLUG这个Action来控制，但Music并没有监听此事件，

    /**     * Broadcast Action: Wired Headset plugged in or unplugged.     *     * <p>The intent will have the following extra values:     * <ul>     *   <li><em>state</em> - 0 for unplugged, 1 for plugged. </li>     *   <li><em>name</em> - Headset type, human readable string </li>     *   <li><em>microphone</em> - 1 if headset has a microphone, 0 otherwise </li>     * </ul>     * </ul>     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String ACTION_HEADSET_PLUG =            "android.intent.action.HEADSET_PLUG";

自己测试了一下，在AndroidManifest.xml中静态注册，是不会生效的，为啥？

一个很简单的解释，如果你的应用还没有运行，这时插入耳机，系统如何把这个消息给这个应用？

因此，"android.intent.action.HEADSET_PLUG"只能通过动态注册来接收此广播消息。

如果让MediaButtonIntentReceiver 还接收"android.intent.action.HEADSET_PLUG"的广播消息，

则MediaButtonIntentReceiver会先收到"android.media.AUDIO_BECOMING_NOISY" 这个消息，然后才会收到"android.intent.action.HEADSET_PLUG"这个消息？

为什么这样，代码层面还没有分析，后面抽空再研究下Android源码。

更多相关文章

随机推荐