public class MediaButtonReceiver extends BroadcastReceiver {
    private static String TAG = "MediaButtonReceiver";

    @Override
    public void onReceive(Context context, Intent intent) {
        // 获得Action
        String intentAction = intent.getAction();
        // 获得KeyEvent对象
        KeyEvent keyEvent = intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
       if (Intent.ACTION_MEDIA_BUTTON.equals(intentAction) && keyEvent != null) {
            try {
                // 获得按键字节码
                int keyCode = keyEvent.getKeyCode();
                // 按下 / 松开 按钮
                int keyAction = keyEvent.getAction();
       // ....很多其他代码

会发现keyEvent 在Android 12中为null，虽然前面有对keyEvent 有判断，但三方平台仍报nullpointException,找到使用的地方，发现调用registerMediaButtonEventReceiver方法

      // 注册的地方
        val audioManager = activity!!.getSystemService(Context.AUDIO_SERVICE) as AudioManager
        val name = ComponentName(activity!!.packageName,
                MediaButtonReceiver::class.java.name)
        audioManager.registerMediaButtonEventReceiver(name)

查看方法源码

    @Deprecated
    public void registerMediaButtonEventReceiver(ComponentName eventReceiver) {
        if (eventReceiver == null) {
            return;
        }
        if (!eventReceiver.getPackageName().equals(getContext().getPackageName())) {
            Log.e(TAG, "registerMediaButtonEventReceiver() error: " +
                    "receiver and context package names don't match");
            return;
        }
        // construct a PendingIntent for the media button and register it
        Intent mediaButtonIntent = new Intent(Intent.ACTION_MEDIA_BUTTON);
        //     the associated intent will be handled by the component being registered
        mediaButtonIntent.setComponent(eventReceiver);
        PendingIntent pi = PendingIntent.getBroadcast(getContext(),
                0/*requestCode, ignored*/, mediaButtonIntent, 0/*flags*/);
        registerMediaButtonIntent(pi, eventReceiver);
    }    @Deprecated
    public void registerMediaButtonEventReceiver(ComponentName eventReceiver) {
        if (eventReceiver == null) {
            return;
        }
        if (!eventReceiver.getPackageName().equals(getContext().getPackageName())) {
            Log.e(TAG, "registerMediaButtonEventReceiver() error: " +
                    "receiver and context package names don't match");
            return;
        }
        // construct a PendingIntent for the media button and register it
        Intent mediaButtonIntent = new Intent(Intent.ACTION_MEDIA_BUTTON);
        //     the associated intent will be handled by the component being registered
        mediaButtonIntent.setComponent(eventReceiver);
        PendingIntent pi = PendingIntent.getBroadcast(getContext(),
                0/*requestCode, ignored*/, mediaButtonIntent, 0/*flags*/);
        registerMediaButtonIntent(pi, eventReceiver);
    }

intent确实没有放EXTRA_KEY_EVENT，该方法末尾调用registerMediaButtonIntent，既然如此，直接调用这个方法不就可以了，自己在intent添加事件？！ audioManager .registerMediaButtonIntent(),调用不了，但是registerMediaButtonEventReceiver方法的参数还可以传pendingIntent, 所以，可以这么用

        val audioManager = activity!!.getSystemService(Context.AUDIO_SERVICE) as AudioManager
        val name = ComponentName(activity!!.packageName,
                MediaButtonReceiver::class.java.name)
//       audioManager.registerMediaButtonEventReceiver(name)


        val intent = Intent(Intent.ACTION_MEDIA_BUTTON)
        intent.component = name
        intent.putExtra(Intent.EXTRA_KEY_EVENT, KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_HEADSETHOOK))
        pendingIntent = PendingIntent.getBroadcast(activity, 0, intent, 0)
//     开始用反射调用registerMediaButtonIntent方法，但发现完全没必要
//        val m = audioManager.javaClass.getMethod("registerMediaButtonIntent",PendingIntent::class.java,ComponentName::class.java)
//        m.invoke(audioManager,pendingIntent,null)
        audioManager.registerMediaButtonEventReceiver(pendingIntent)

最后记得不用的时候
audioManager.unregisterMediaButtonEventReceiver(pendingIntent)