用BroadcastReceiver接收SD卡状态变化的事件时，总是无法收到事件通知，经查是少了以下红色语句。

原因涉及Android中IntentFilter匹配原则问题。这篇文章讲得比较清楚 , 这里就不再赘述。

......

IntentFilter sdcardActionFilter = new IntentFilter();

sdcardActionFilter.addAction(Intent.ACTION_MEDIA_BAD_REMOVAL);

sdcardActionFilter.addAction(Intent.ACTION_MEDIA_REMOVED);

sdcardActionFilter.addAction(Intent.ACTION_MEDIA_UNMOUNTED);

sdcardActionFilter.addDataScheme("file");

SDcardListenerReceiver sdCardStateReceiver = new SDcardListenerReceiver();

registerReceiver(sdCardStateReceiver, sdcardActionFilter);

......

static final class SDcardListenerReceiver extends BroadcastReceiver {

@Override

public void onReceive(Context context, Intent intent) {

String action = intent.getAction();

if (action.equals(Intent.ACTION_MEDIA_REMOVED)

　　|| action.equals(Intent.ACTION_MEDIA_UNMOUNTED)

　　|| action.equals(Intent.ACTION_MEDIA_BAD_REMOVAL)

) {

...... 

}

}

}