Android Wifi Direct onPeersAvailable不显示任何内容

我正在尝试使用Wifi Direct开发一个简单的应用程序。问题是我无法使用onPeersAvailable方法获取可用对等方的列表。我尝试了这里和这里提到的解决方案，但是没有运气。日志上什么也没有，尝试使用Toast代替日志，但屏幕上也没有任何显示。这是我的Main和BroadCastReceiver类。

主类：

public class MainActivity extends AppCompatActivity {

private final String TAG = this.getClass().toString();

WifiP2pManager mManager;
WifiP2pManager.Channel mChannel;
BroadcastReceiver mReceiver;
IntentFilter mIntentFilter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mManager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
    mChannel = mManager.initialize(this, getMainLooper(), null);
    mReceiver = new WiFiDirectBroadcastReceiver(mManager, mChannel, this);

    mIntentFilter = new IntentFilter();
    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);

    Button btn_discover = (Button) findViewById(R.id.btn_discover);
    btn_discover.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            mManager.discoverPeers(mChannel, new WifiP2pManager.ActionListener() {
                @Override
                public void onSuccess() {
                    /*Toast.makeText(getApplicationContext(), "Discovery is a success.",
                            Toast.LENGTH_SHORT).show();*/
                    //startActivity(new Intent(Settings.ACTION_WIRELESS_SETTINGS));
                }

                @Override
                public void onFailure(int reasonCode) {
                    Toast.makeText(getApplicationContext(), "Discovery is a failure "+reasonCode,
                            Toast.LENGTH_SHORT).show();
                }
            });
        }
    });
}

/* register the broadcast receiver with the intent values to be matched */
@Override
protected void onResume() {
    super.onResume();
    registerReceiver(mReceiver, mIntentFilter);
}
/* unregister the broadcast receiver */
@Override
protected void onPause() {
    super.onPause();
    unregisterReceiver(mReceiver);
}}

BroadCastReceiver类：

public class WiFiDirectBroadcastReceiver extends BroadcastReceiver {
private final String LOG_TAG = this.toString();
private WifiP2pManager mManager;
private WifiP2pManager.Channel mChannel;
private MainActivity mActivity;

public WiFiDirectBroadcastReceiver(WifiP2pManager manager, WifiP2pManager.Channel channel,
                                   MainActivity activity) {
    super();
    this.mManager = manager;
    this.mChannel = channel;
    this.mActivity = activity;
}



@Override
public void onReceive(Context context, Intent intent) {
    String action = intent.getAction();

    if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
        int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
        if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) {
            Log.i(LOG_TAG, "Wifi Direct is enabled");
        } else {
            Log.i(LOG_TAG, "Wifi Direct is not enabled");
        }
    } else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {
        // request available peers from the wifi p2p manager. This is an
        // asynchronous call and the calling activity is notified with a
        // callback on PeerListListener.onPeersAvailable()
        if (mManager != null) {
            mManager.requestPeers(mChannel, new WifiP2pManager.PeerListListener() {
                @Override
                public void onPeersAvailable(WifiP2pDeviceList wifiP2pDeviceList) {
                    Log.i(LOG_TAG, "Found some peers!!! "+wifiP2pDeviceList.getDeviceList().size());
                }
            });
        }
    } else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {
        // Respond to new connection or disconnections
    } else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {
        // Respond to this device's wifi state changing
    }
}}

我确定我的设备（运行Android 4.4.4的2012 Nexus 7）支持Wifi Direct。