Creating P2P Connections with Wi-Fi

Wi-Fi P2P allows your application to quickly find and interact with nearby devices, at a range beyond the capabilities of Bluetooth.

The Wi-Fi peer-to-peer (P2P) APIs allow applications to connect to nearby devices without needing to connect to a network or hotspot (Android's Wi-Fi P2P framework complies with the Wi-Fi Direct™ certification program). If your app is designed to be a part of a secure, near-range network, Wi-Fi Direct is a more suitable option than traditional Wi-Fi ad-hoc networking for the following reasons:

• Wi-Fi Direct supports WPA2 encryption. (Some ad-hoc networks support only WEP encryption.)
• Devices can broadcast the services that they provide, which helps other devices discover suitable peers more easily.
• When determining which device should be the group owner for the network, Wi-Fi Direct examines each device's power management, UI, and service capabilities and uses this information to choose the device that can handle server responsibilities most effectively.
• Android doesn't support Wi-Fi ad-hoc mode.

This lesson shows you how to find and connect to nearby devices using Wi-Fi P2P.

Set Up Application Permissions

In order to use Wi-Fi P2P, add the ACCESS_COARSE_LOCATION, CHANGE_WIFI_STATE, ACCESS_WIFI_STATE, and INTERNET permissions to your manifest. Wi-Fi P2P doesn't require an internet connection, but it does use standard Java sockets, which requires the INTERNET permission. So you need the following permissions to use Wi-Fi P2P:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.android.nsdchat"
    ...
    <uses-permission
        android:required="true"
        android:name="android.permission.ACCESS_COARSE_LOCATION"/>
    <uses-permission
        android:required="true"
        android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission
        android:required="true"
        android:name="android.permission.CHANGE_WIFI_STATE"/>
    <uses-permission
        android:required="true"
        android:name="android.permission.INTERNET"/>
    ...

Set Up a Broadcast Receiver and Peer-to-Peer Manager

To use Wi-Fi P2P, you need to listen for broadcast intents that tell your application when certain events have occurred. In your application, instantiate an IntentFilter and set it to listen for the following:

WIFI_P2P_STATE_CHANGED_ACTION

Indicates whether Wi-Fi P2P is enabled

WIFI_P2P_PEERS_CHANGED_ACTION

Indicates that the available peer list has changed.

WIFI_P2P_CONNECTION_CHANGED_ACTION

Indicates the state of Wi-Fi P2P connectivity has changed.

WIFI_P2P_THIS_DEVICE_CHANGED_ACTION

Indicates this device's configuration details have changed.

private final IntentFilter intentFilter = new IntentFilter();
...
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    //  Indicates a change in the Wi-Fi P2P status.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);

    // Indicates a change in the list of available peers.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);

    // Indicates the state of Wi-Fi P2P connectivity has changed.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);

    // Indicates this device's details have changed.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);

    ...
}

At the end of the onCreate() method, get an instance of the WifiP2pManager, and call its initialize() method. This method returns a WifiP2pManager.Channel object, which you'll use later to connect your app to the Wi-Fi P2P framework.

@Override

Channel mChannel;

public void onCreate(Bundle savedInstanceState) {
    ....
    mManager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
    mChannel = mManager.initialize(this, getMainLooper(), null);
}

Now create a new BroadcastReceiver class that you'll use to listen for changes to the System's Wi-Fi P2P state. In the onReceive() method, add a condition to handle each P2P state change listed above.

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
            // Determine if Wifi P2P mode is enabled or not, alert
            // the Activity.
            int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
            if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) {
                activity.setIsWifiP2pEnabled(true);
            } else {
                activity.setIsWifiP2pEnabled(false);
            }
        } else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {

            // The peer list has changed!  We should probably do something about
            // that.

        } else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {

            // Connection state changed!  We should probably do something about
            // that.

        } else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {
            DeviceListFragment fragment = (DeviceListFragment) activity.getFragmentManager()
                    .findFragmentById(R.id.frag_list);
            fragment.updateThisDevice((WifiP2pDevice) intent.getParcelableExtra(
                    WifiP2pManager.EXTRA_WIFI_P2P_DEVICE));

        }
    }

Finally, add code to register the intent filter and broadcast receiver when your main activity is active, and unregister them when the activity is paused. The best place to do this is the onResume() and onPause() methods.

    /** register the BroadcastReceiver with the intent values to be matched */
    @Override
    public void onResume() {
        super.onResume();
        receiver = new WiFiDirectBroadcastReceiver(mManager, mChannel, this);
        registerReceiver(receiver, intentFilter);
    }

    @Override
    public void onPause() {
        super.onPause();
        unregisterReceiver(receiver);
    }

Initiate Peer Discovery

To start searching for nearby devices with Wi-Fi P2P, call discoverPeers(). This method takes the following arguments:

• The WifiP2pManager.Channel you received back when you initialized the peer-to-peer mManager
• An implementation of WifiP2pManager.ActionListener with methods the system invokes for successful and unsuccessful discovery.

mManager.discoverPeers(mChannel, new WifiP2pManager.ActionListener() {

        @Override
        public void onSuccess() {
            // Code for when the discovery initiation is successful goes here.
            // No services have actually been discovered yet, so this method
            // can often be left blank.  Code for peer discovery goes in the
            // onReceive method, detailed below.
        }

        @Override
        public void onFailure(int reasonCode) {
            // Code for when the discovery initiation fails goes here.
            // Alert the user that something went wrong.
        }
});

Keep in mind that this only initiates peer discovery. The discoverPeers() method starts the discovery process and then immediately returns. The system notifies you if the peer discovery process is successfully initiated by calling methods in the provided action listener. Also, discovery will remain active until a connection is initiated or a P2P group is formed.

Fetch the List of Peers

Now write the code that fetches and processes the list of peers. First implement the WifiP2pManager.PeerListListener interface, which provides information about the peers that Wi-Fi P2P has detected. This information also allows your app to determine when peers join or leave the network. The following code snippet illustrates these operations related to peers:

    private List<WifiP2pDevice> peers = new ArrayList<WifiP2pDevice>();
    ...

    private PeerListListener peerListListener = new PeerListListener() {
        @Override
        public void onPeersAvailable(WifiP2pDeviceList peerList) {

            List<WifiP2pDevice> refreshedPeers = peerList.getDeviceList();
            if (!refreshedPeers.equals(peers)) {
                peers.clear();
                peers.addAll(refreshedPeers);

                // If an AdapterView is backed by this data, notify it
                // of the change.  For instance, if you have a ListView of
                // available peers, trigger an update.
                ((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged();

                // Perform any other updates needed based on the new list of
                // peers connected to the Wi-Fi P2P network.
            }

            if (peers.size() == 0) {
                Log.d(WiFiDirectActivity.TAG, "No devices found");
                return;
            }
        }
    }

Now modify your broadcast receiver's onReceive() method to call requestPeers() when an intent with the action WIFI_P2P_PEERS_CHANGED_ACTION is received. You need to pass this listener into the receiver somehow. One way is to send it as an argument to the broadcast receiver's constructor.

public void onReceive(Context context, Intent intent) {
    ...
    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, peerListListener);
        }
        Log.d(WiFiDirectActivity.TAG, "P2P peers changed");
    }...
}

Now, an intent with the action WIFI_P2P_PEERS_CHANGED_ACTION intent will trigger a request for an updated peer list.

Connect to a Peer

In order to connect to a peer, create a new WifiP2pConfig object, and copy data into it from the WifiP2pDevice representing the device you want to connect to. Then call the connect() method.

    @Override
    public void connect() {
        // Picking the first device found on the network.
        WifiP2pDevice device = peers.get(0);

        WifiP2pConfig config = new WifiP2pConfig();
        config.deviceAddress = device.deviceAddress;
        config.wps.setup = WpsInfo.PBC;

        mManager.connect(mChannel, config, new ActionListener() {

            @Override
            public void onSuccess() {
                // WiFiDirectBroadcastReceiver will notify us. Ignore for now.
            }

            @Override
            public void onFailure(int reason) {
                Toast.makeText(WiFiDirectActivity.this, "Connect failed. Retry.",
                        Toast.LENGTH_SHORT).show();
            }
        });
    }

If each of the devices in your group supports Wi-Fi direct, you don't need to explicitly ask for the group's password when connecting. To allow a device that doesn't support Wi-Fi Direct to join a group, however, you need to retrieve this password by calling requestGroupInfo(), as shown in the following code snippet:

mManager.requestGroupInfo(mChannel, new GroupInfoListener() {
  @Override
  public void onGroupInfoAvailable(WifiP2pGroup group) {
      String groupPassword = group.getPassphrase();
  }
});

Note that the WifiP2pManager.ActionListener implemented in the connect() method only notifies you when the initiation succeeds or fails. To listen for changes in connection state, implement the WifiP2pManager.ConnectionInfoListener interface. Its onConnectionInfoAvailable() callback will notify you when the state of the connection changes. In cases where multiple devices are going to be connected to a single device (like a game with 3 or more players, or a chat app), one device will be designated the "group owner". You can designate a particular device as the network's group owner by following the steps in the Create a Group section.

    @Override
    public void onConnectionInfoAvailable(final WifiP2pInfo info) {

        // InetAddress from WifiP2pInfo struct.
        InetAddress groupOwnerAddress = info.groupOwnerAddress.getHostAddress());

        // After the group negotiation, we can determine the group owner
        // (server).
        if (info.groupFormed && info.isGroupOwner) {
            // Do whatever tasks are specific to the group owner.
            // One common case is creating a group owner thread and accepting
            // incoming connections.
        } else if (info.groupFormed) {
            // The other device acts as the peer (client). In this case,
            // you'll want to create a peer thread that connects
            // to the group owner.
        }
    }

Now go back to the onReceive() method of the broadcast receiver, and modify the section that listens for a WIFI_P2P_CONNECTION_CHANGED_ACTION intent. When this intent is received, call requestConnectionInfo(). This is an asynchronous call, so results will be received by the connection info listener you provide as a parameter.

        ...
        } else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {

            if (mManager == null) {
                return;
            }

            NetworkInfo networkInfo = (NetworkInfo) intent
                    .getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO);

            if (networkInfo.isConnected()) {

                // We are connected with the other device, request connection
                // info to find group owner IP

                mManager.requestConnectionInfo(mChannel, connectionListener);
            }
            ...

Create a Group

If you want the device running your app to serve as the group owner for a network that includes legacy devices—that is, devices that don't support Wi-Fi Direct—you follow the same sequence of steps as in the Connect to a Peer section, except you create a new WifiP2pManager.ActionListener using createGroup() instead of connect(). The callback handling within the WifiP2pManager.ActionListener is the same, as shown in the following code snippet:

mManager.createGroup(mChannel, new WifiP2pManager.ActionListener() {
    @Override
    public void onSuccess() {
        // Device is ready to accept incoming connections from peers.
    }

    @Override
    public void onFailure(int reason) {
        Toast.makeText(WiFiDirectActivity.this, "P2P group creation failed. Retry.",
                Toast.LENGTH_SHORT).show();
    }
});

Note: If all the devices in a network support Wi-Fi Direct, you can use the connect() method on each device because the method then creates the group and selects a group owner automatically.

After you create a group, you can call requestGroupInfo() to retrieve details about the peers on the network, including device names and connection statuses.