Android 如何判断蓝牙设备是否已连接？我的代码不是'；行不通

我正在尝试侦听蓝牙连接/断开事件，以确定是否连接了蓝牙设备。我正试图这样做，这样我的应用程序就可以在旧的android版本上运行

我在舱单中登记了接收人：

<receiver
        android:name=".BluetoothReceiver">
        <intent-filter>
            <action android:name="android.bluetooth.device.action.ACL_CONNECTED" />

        </intent-filter>
</receiver>

---

但当连接和断开蓝牙时，什么也不会发生。我做错了什么？

如果是蓝牙耳机，请参阅

public class BluetoothReceiver extends BroadcastReceiver{
public final static String TAG = "BluetoothReciever";

public void onReceive(Context context, Intent intent)
{

    Log.d(TAG, "Bluetooth Intent Recieved");

    final BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
    String action = intent.getAction();

    if (BluetoothDevice.ACTION_ACL_CONNECTED.equalsIgnoreCase(action))
    {
        Log.d(TAG, "Connected to " + device.getName());
    }

    if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equalsIgnoreCase(action))
    {
        Log.d(TAG, "Disconnected from " + device.getName());
    }
}}