Wi-Fi Direct (P2P) allows Android 4.0 (API level 14) and higher devices with the appropriate hardware to connect directly to each other via Wi-Fi without an intermediate access point. Using these APIs, you can discover and connect to other devices when each device supports Wi-Fi P2P, then communicate over a speedy connection across distances much longer than a Bluetooth connection. This is useful for applications that share data among users, such as a multiplayer game or a photo sharing application.
The Wi-Fi P2P APIs consist of the following main parts:
Methods that allow you to discover, request, and connect to peers are defined in the
WifiP2pManager
class.Listeners that allow you to be notified of the success or failure of
WifiP2pManager
method calls. When callingWifiP2pManager
methods, each method can receive a specific listener passed in as a parameter.Intents that notify you of specific events detected by the Wi-Fi P2P framework, such as a dropped connection or a newly discovered peer.
You often use these three main components of the APIs together. For example, you
can provide a
WifiP2pManager.ActionListener
to a call to
discoverPeers()
,
so that you can be notified with the
ActionListener.onSuccess()
and
ActionListener.onFailure()
methods. A
WIFI_P2P_PEERS_CHANGED_ACTION
intent is also broadcast if the discoverPeers()
method discovers that the
peers list has changed.
API overview
The WifiP2pManager
class
provides methods to allow you to interact with the Wi-Fi hardware on your
device to do things like discover and connect to peers. The following actions
are available:
Table 1.Wi-Fi P2P Methods
Method | Description |
---|---|
initialize()
|
Registers the application with the Wi-Fi framework. This must be called before calling any other Wi-Fi P2P method. |
connect()
|
Starts a peer-to-peer connection with a device with the specified configuration. |
cancelConnect()
|
Cancels any ongoing peer-to-peer group negotiation. |
requestConnectInfo()
|
Requests a device's connection information. |
createGroup()
|
Creates a peer-to-peer group with the current device as the group owner. |
removeGroup()
|
Removes the current peer-to-peer group. |
requestGroupInfo()
|
Requests peer-to-peer group information. |
discoverPeers()
|
Initiates peer discovery. |
requestPeers()
|
Requests the current list of discovered peers. |
WifiP2pManager
methods let you pass in a listener, so that the Wi-Fi P2P framework can notify
your activity of the status of a call. The available listener interfaces and the
corresponding
WifiP2pManager
method calls that use the listeners are described in the following table:
Table 2. Wi-Fi P2P Listeners
The Wi-Fi P2P APIs define intents that are broadcast when certain Wi-Fi P2P events happen, such as when a new peer is discovered or when a device's Wi-Fi state changes. You can register to receive these intents in your application by creating a broadcast receiver that handles these intents:
Table 3. Wi-Fi P2P Intents
Intent | Description |
---|---|
WIFI_P2P_CONNECTION_CHANGED_ACTION
|
Broadcast when the state of the device's Wi-Fi connection changes. |
WIFI_P2P_PEERS_CHANGED_ACTION
|
Broadcast when you call
discoverPeers() .
You usually want to call
requestPeers()
to get an updated list of peers if you handle this intent in your
application.
|
WIFI_P2P_STATE_CHANGED_ACTION
|
Broadcast when Wi-Fi P2P is enabled or disabled on the device. |
WIFI_P2P_THIS_DEVICE_CHANGED_ACTION
|
Broadcast when a device's details have changed, such as the device's name. |
Create a broadcast receiver for Wi-Fi P2P intents
A broadcast receiver allows you to receive intents broadcast by the Android system, so that your application can respond to events that you are interested in. The basic steps for creating a broadcast receiver to handle Wi-Fi P2P intents are as follows:
Create a class that extends the
BroadcastReceiver
class. For the class' constructor, you most likely want to have parameters for theWifiP2pManager
,WifiP2pManager.Channel
, and the activity that this broadcast receiver will be registered in. This allows the broadcast receiver to send updates to the activity as well as have access to the Wi-Fi hardware and a communication channel if needed.In the broadcast receiver, check for the intents that you are interested in
onReceive()
. Carry out any necessary actions depending on the intent that is received. For example, if the broadcast receiver receives aWIFI_P2P_PEERS_CHANGED_ACTION
intent, you can call therequestPeers()
method to get a list of the currently discovered peers.
The following code shows you how to create a typical broadcast receiver. The
broadcast receiver takes a
WifiP2pManager
object and an
activity as arguments and uses these two classes to appropriately carry out the
needed actions when the broadcast receiver receives an intent:
Kotlin
/** * A BroadcastReceiver that notifies of important Wi-Fi p2p events. */ class WiFiDirectBroadcastReceiver( private val manager: WifiP2pManager, private val channel: WifiP2pManager.Channel, private val activity: MyWifiActivity ) : BroadcastReceiver() { override fun onReceive(context: Context, intent: Intent) { val action: String = intent.action when (action) { WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION -> { // Check to see if Wi-Fi is enabled and notify appropriate activity } WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION -> { // Call WifiP2pManager.requestPeers() to get a list of current peers } WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION -> { // Respond to new connection or disconnections } WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION -> { // Respond to this device's wifi state changing } } } }
Java
/** * A BroadcastReceiver that notifies of important Wi-Fi p2p events. */ public class WiFiDirectBroadcastReceiver extends BroadcastReceiver { private WifiP2pManager manager; private Channel channel; private MyWiFiActivity activity; public WiFiDirectBroadcastReceiver(WifiP2pManager manager, Channel channel, MyWifiActivity activity) { super(); this.manager = manager; this.channel = channel; this.activity = activity; } @Override public void onReceive(Context context, Intent intent) { String action = intent.getAction(); if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) { // Check to see if Wi-Fi is enabled and notify appropriate activity } else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) { // Call WifiP2pManager.requestPeers() to get a list of current peers } 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 } } }
With Android 10, the following broadcast intents were changed from sticky to non-sticky:
WIFI_P2P_CONNECTION_CHANGED_ACTION
- Applications can use
requestConnectionInfo()
,requestNetworkInfo()
, orrequestGroupInfo()
to retrieve the current connection information. WIFI_P2P_THIS_DEVICE_CHANGED_ACTION
- Applications can use
requestDeviceInfo()
to retrieve the current connection information.
Create a Wi-Fi P2P application
Creating a Wi-Fi P2P application involves creating and registering a broadcast receiver for your application, discovering peers, connecting to a peer, and transferring data to a peer. The following sections describe how to do this.
Initial setup
Before using the Wi-Fi P2P APIs, you must ensure that your application can
access the hardware and that the device supports the Wi-Fi P2P protocol. If
Wi-Fi P2P is supported, you can obtain an instance of
WifiP2pManager
, create and
register your broadcast receiver, and begin using the Wi-Fi P2P APIs.
Request permission to use the Wi-Fi hardware on the device and also declare your application to have the correct minimum SDK version in the Android manifest:
<uses-sdk android:minSdkVersion="14" /> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" /> <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" /> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
Besides the preceding permissions, the following APIs also require Location Mode to be enabled:
Check to see if Wi-Fi P2P is on and supported. A good place to check this is in your broadcast receiver when it receives the
WIFI_P2P_STATE_CHANGED_ACTION
intent. Notify your activity of the Wi-Fi P2P state and react accordingly:Kotlin
override fun onReceive(context: Context, intent: Intent) { ... val action: String = intent.action when (action) { WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION -> { val state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1) when (state) { WifiP2pManager.WIFI_P2P_STATE_ENABLED -> { // Wifi P2P is enabled } else -> { // Wi-Fi P2P is not enabled } } } } ... }
Java
@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) { // Wifi P2P is enabled } else { // Wi-Fi P2P is not enabled } } ... }
In your activity's
onCreate()
method, obtain an instance ofWifiP2pManager
and register your application with the Wi-Fi P2P framework by callinginitialize()
. This method returns aWifiP2pManager.Channel
, which is used to connect your application to the Wi-Fi P2P framework. You should also create an instance of your broadcast receiver with theWifiP2pManager
andWifiP2pManager.Channel
objects along with a reference to your activity. This allows your broadcast receiver to notify your activity of interesting events and update it accordingly. It also lets you manipulate the device's Wi-Fi state if necessary:Kotlin
val manager: WifiP2pManager? by lazy(LazyThreadSafetyMode.NONE) { getSystemService(Context.WIFI_P2P_SERVICE) as WifiP2pManager? } var channel: WifiP2pManager.Channel? = null var receiver: BroadcastReceiver? = null override fun onCreate(savedInstanceState: Bundle?) { ... channel = manager?.initialize(this, mainLooper, null) channel?.also { channel -> receiver = WiFiDirectBroadcastReceiver(manager, channel, this) } }
Java
WifiP2pManager manager; Channel channel; BroadcastReceiver receiver; ... @Override protected void onCreate(Bundle savedInstanceState){ ... manager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE); channel = manager.initialize(this, getMainLooper(), null); receiver = new WiFiDirectBroadcastReceiver(manager, channel, this); ... }
Create an intent filter and add the same intents that your broadcast receiver checks for:
Kotlin
val intentFilter = IntentFilter().apply { addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION) addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION) addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION) addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION) }
Java
IntentFilter intentFilter; ... @Override protected void onCreate(Bundle savedInstanceState){ ... intentFilter = new IntentFilter(); intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION); intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION); intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION); intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION); ... }
Register the broadcast receiver in the
onResume()
method of your activity and unregister it in theonPause()
method of your activity:Kotlin
/* register the broadcast receiver with the intent values to be matched */ override fun onResume() { super.onResume() receiver?.also { receiver -> registerReceiver(receiver, intentFilter) } } /* unregister the broadcast receiver */ override fun onPause() { super.onPause() receiver?.also { receiver -> unregisterReceiver(receiver) } }
Java
/* register the broadcast receiver with the intent values to be matched */ @Override protected void onResume() { super.onResume(); registerReceiver(receiver, intentFilter); } /* unregister the broadcast receiver */ @Override protected void onPause() { super.onPause(); unregisterReceiver(receiver); }
When you have obtained a
WifiP2pManager.Channel
and set up a broadcast receiver, your application can make Wi-Fi P2P method calls and receive Wi-Fi P2P intents.You can now implement your application and use the Wi-Fi P2P features by calling the methods in
WifiP2pManager
. The next sections describe how to do common actions such as discovering and connecting to peers.
Discover peers
To discover peers that are available to connect to, call
discoverPeers()
to detect available peers that are in range. The call to this function is
asynchronous and a success or failure is communicated to your application with
onSuccess()
and
onFailure()
if you created a
WifiP2pManager.ActionListener
.
The
onSuccess()
method only notifies you that the discovery process succeeded and does not
provide any information about the actual peers that it discovered, if any:
Kotlin
manager?.discoverPeers(channel, object : WifiP2pManager.ActionListener { override fun onSuccess() { ... } override fun onFailure(reasonCode: Int) { ... } })
Java
manager.discoverPeers(channel, new WifiP2pManager.ActionListener() { @Override public void onSuccess() { ... } @Override public void onFailure(int reasonCode) { ... } });
If the discovery process succeeds and detects peers, the system broadcasts the
WIFI_P2P_PEERS_CHANGED_ACTION
intent, which you can listen for in a broadcast receiver to obtain a list of
peers. When your application receives the
WIFI_P2P_PEERS_CHANGED_ACTION
intent, you can request a list of the discovered peers with
requestPeers()
.
The following code shows how to set this up:
Kotlin
override fun onReceive(context: Context, intent: Intent) { val action: String = intent.action when (action) { ... WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION -> { manager?.requestPeers(channel) { peers: WifiP2pDeviceList? -> // Handle peers list } } ... } }
Java
PeerListListener myPeerListListener; ... 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 (manager != null) { manager.requestPeers(channel, myPeerListListener); } }
The
requestPeers()
method is also asynchronous and can notify your activity when a list of peers is
available with
onPeersAvailable()
,
which is defined in the
WifiP2pManager.PeerListListener
interface. The
onPeersAvailable()
method provides you with an
WifiP2pDeviceList
,
which you can iterate through to find the peer that you want to connect to.
Connect to peers
When you have figured out the device that you want to connect to after obtaining
a list of possible peers, call the
connect()
method to connect to the device. This method call requires a
WifiP2pConfig
object that contains the information of the device to connect to. You can be
notified of a connection success or failure through the
WifiP2pManager.ActionListener
.
The following code shows you how to create a connection to a desired device:
Kotlin
val device: WifiP2pDevice = ... val config = WifiP2pConfig() config.deviceAddress = device.deviceAddress channel?.also { channel -> manager?.connect(channel, config, object : WifiP2pManager.ActionListener { override fun onSuccess() { //success logic } override fun onFailure(reason: Int) { //failure logic } } )}
Java
//obtain a peer from the WifiP2pDeviceList WifiP2pDevice device; WifiP2pConfig config = new WifiP2pConfig(); config.deviceAddress = device.deviceAddress; manager.connect(channel, config, new ActionListener() { @Override public void onSuccess() { //success logic } @Override public void onFailure(int reason) { //failure logic } });
Transfer data
Once a connection is established, you can transfer data between the devices with sockets. The basic steps of transferring data are as follows:
Create a
ServerSocket
. This socket waits for a connection from a client on a specified port and blocks until it happens, so do this in a background thread.Create a client
Socket
. The client uses the IP address and port of the server socket to connect to the server device.Send data from the client to the server. When the client socket successfully connects to the server socket, you can send data from the client to the server with byte streams.
The server socket waits for a client connection (with the
accept()
method). This call blocks until a client connects, so call this is another thread. When a connection happens, the server device can receive the data from the client. Carry out any actions with this data, such as saving it to a file or presenting it to the user.
The following example, modified from the Wi-Fi P2P Demo sample, shows you how to create this client-server socket communication and transfer JPEG images from a client to a server with a service. For a complete working example, compile and run the sample.
Kotlin
class FileServerAsyncTask( private val context: Context, private var statusText: TextView ) : AsyncTask<Void, Void, String?>() { override fun doInBackground(vararg params: Void): String? { /** * Create a server socket. */ val serverSocket = ServerSocket(8888) return serverSocket.use { /** * Wait for client connections. This call blocks until a * connection is accepted from a client. */ val client = serverSocket.accept() /** * If this code is reached, a client has connected and transferred data * Save the input stream from the client as a JPEG file */ val f = File(Environment.getExternalStorageDirectory().absolutePath + "/${context.packageName}/wifip2pshared-${System.currentTimeMillis()}.jpg") val dirs = File(f.parent) dirs.takeIf { it.doesNotExist() }?.apply { mkdirs() } f.createNewFile() val inputstream = client.getInputStream() copyFile(inputstream, FileOutputStream(f)) serverSocket.close() f.absolutePath } } private fun File.doesNotExist(): Boolean = !exists() /** * Start activity that can handle the JPEG image */ override fun onPostExecute(result: String?) { result?.run { statusText.text = "File copied - $result" val intent = Intent(android.content.Intent.ACTION_VIEW).apply { setDataAndType(Uri.parse("file://$result"), "image/*") } context.startActivity(intent) } } }
Java
public static class FileServerAsyncTask extends AsyncTask { private Context context; private TextView statusText; public FileServerAsyncTask(Context context, View statusText) { this.context = context; this.statusText = (TextView) statusText; } @Override protected String doInBackground(Void... params) { try { /** * Create a server socket and wait for client connections. This * call blocks until a connection is accepted from a client */ ServerSocket serverSocket = new ServerSocket(8888); Socket client = serverSocket.accept(); /** * If this code is reached, a client has connected and transferred data * Save the input stream from the client as a JPEG file */ final File f = new File(Environment.getExternalStorageDirectory() + "/" + context.getPackageName() + "/wifip2pshared-" + System.currentTimeMillis() + ".jpg"); File dirs = new File(f.getParent()); if (!dirs.exists()) dirs.mkdirs(); f.createNewFile(); InputStream inputstream = client.getInputStream(); copyFile(inputstream, new FileOutputStream(f)); serverSocket.close(); return f.getAbsolutePath(); } catch (IOException e) { Log.e(WiFiDirectActivity.TAG, e.getMessage()); return null; } } /** * Start activity that can handle the JPEG image */ @Override protected void onPostExecute(String result) { if (result != null) { statusText.setText("File copied - " + result); Intent intent = new Intent(); intent.setAction(android.content.Intent.ACTION_VIEW); intent.setDataAndType(Uri.parse("file://" + result), "image/*"); context.startActivity(intent); } } }
On the client, connect to the server socket with a client socket and transfer data. This example transfers a JPEG file on the client device's file system.
Kotlin
val context = applicationContext val host: String val port: Int val len: Int val socket = Socket() val buf = ByteArray(1024) ... try { /** * Create a client socket with the host, * port, and timeout information. */ socket.bind(null) socket.connect((InetSocketAddress(host, port)), 500) /** * Create a byte stream from a JPEG file and pipe it to the output stream * of the socket. This data is retrieved by the server device. */ val outputStream = socket.getOutputStream() val cr = context.contentResolver val inputStream: InputStream = cr.openInputStream(Uri.parse("path/to/picture.jpg")) while (inputStream.read(buf).also { len = it } != -1) { outputStream.write(buf, 0, len) } outputStream.close() inputStream.close() } catch (e: FileNotFoundException) { //catch logic } catch (e: IOException) { //catch logic } finally { /** * Clean up any open sockets when done * transferring or if an exception occurred. */ socket.takeIf { it.isConnected }?.apply { close() } }
Java
Context context = this.getApplicationContext(); String host; int port; int len; Socket socket = new Socket(); byte buf[] = new byte[1024]; ... try { /** * Create a client socket with the host, * port, and timeout information. */ socket.bind(null); socket.connect((new InetSocketAddress(host, port)), 500); /** * Create a byte stream from a JPEG file and pipe it to the output stream * of the socket. This data is retrieved by the server device. */ OutputStream outputStream = socket.getOutputStream(); ContentResolver cr = context.getContentResolver(); InputStream inputStream = null; inputStream = cr.openInputStream(Uri.parse("path/to/picture.jpg")); while ((len = inputStream.read(buf)) != -1) { outputStream.write(buf, 0, len); } outputStream.close(); inputStream.close(); } catch (FileNotFoundException e) { //catch logic } catch (IOException e) { //catch logic } /** * Clean up any open sockets when done * transferring or if an exception occurred. */ finally { if (socket != null) { if (socket.isConnected()) { try { socket.close(); } catch (IOException e) { //catch logic } } } }