page.title=Using Wi-Fi P2P for Service Discovery
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<h2>This lesson teaches you to</h2>
<ol>
<li><a href="#manifest">Set Up the Manifest</a></li>
<li><a href="#register">Add a Local Service</a></li>
<li><a href="#discover">Discover Nearby Services</a></li>
</ol>
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<p>The first lesson in this class, <a href="nsd.html">Using Network Service
Discovery</a>, showed you
how to discover services that are connected to a local network. However, using
Wi-Fi Peer-to-Peer (P2P) Service Discovery allows you to discover the services of nearby devices
directly, without being connected to a network. You can also advertise the services
running on your device. These capabilities help you communicate between apps,
even when no local network or hotspot is available.</p>
<p>While this set of APIs is similar in purpose to the Network Service Discovery
APIs outlined in a previous lesson, implementing them in code is very different.
This lesson shows you how to discover services available from other devices,
using Wi-Fi P2P. The lesson assumes that you're already familiar with the
<a href="{@docRoot}guide/topics/connectivity/wifip2p.html">Wi-Fi P2P</a> API.</p>
<h2 id="manifest">Set Up the Manifest</h2>
<p>In order to use Wi-Fi P2P, add the {@link
android.Manifest.permission#CHANGE_WIFI_STATE}, {@link
android.Manifest.permission#ACCESS_WIFI_STATE},
and {@link android.Manifest.permission#INTERNET}
permissions to your manifest. Even though Wi-Fi P2P doesn't require an
Internet connection, it uses standard Java sockets, and using these in Android
requires the requested permissions.</p>
<pre>
<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_WIFI_STATE"/>
<uses-permission
android:required="true"
android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission
android:required="true"
android:name="android.permission.INTERNET"/>
...
</pre>
<h2 id="register">Add a Local Service</h2>
<p>If you're providing a local service, you need to register it for
service discovery. Once your local service is registered, the framework
automatically responds to service discovery requests from peers.</p>
<p>To create a local service:</p>
<ol>
<li>Create a
{@link android.net.wifi.p2p.nsd.WifiP2pServiceInfo} object.</li>
<li>Populate it with information about your service.</li>
<li>Call {@link
android.net.wifi.p2p.WifiP2pManager#addLocalService(WifiP2pManager.Channel,
WifiP2pServiceInfo, WifiP2pManager.ActionListener) addLocalService()} to register the local
service for service discovery.</li>
</ol>
<pre>
private void startRegistration() {
// Create a string map containing information about your service.
Map<String,String> record = new HashMap<String,String>();
record.put("listenport", String.valueOf(SERVER_PORT));
record.put("buddyname", "John Doe" + (int) (Math.random() * 1000));
record.put("available", "visible");
// Service information. Pass it an instance name, service type
// _protocol._transportlayer , and the map containing
// information other devices will want once they connect to this one.
WifiP2pDnsSdServiceInfo serviceInfo =
WifiP2pDnsSdServiceInfo.newInstance("_test", "_presence._tcp", record);
// Add the local service, sending the service info, network channel,
// and listener that will be used to indicate success or failure of
// the request.
mManager.addLocalService(channel, serviceInfo, new ActionListener() {
@Override
public void onSuccess() {
// Command successful! Code isn't necessarily needed here,
// Unless you want to update the UI or add logging statements.
}
@Override
public void onFailure(int arg0) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
}
});
}
</pre>
<h2 id="discover">Discover Nearby Services</h2>
<p>Android uses callback methods to notify your application of available services, so
the first thing to do is set those up. Create a {@link
android.net.wifi.p2p.WifiP2pManager.DnsSdTxtRecordListener} to listen for
incoming records. This record can optionally be broadcast by other
devices. When one comes in, copy the device address and any other
relevant information you want into a data structure external to the current
method, so you can access it later. The following example assumes that the
record contains a "buddyname" field, populated with the user's identity.</p>
<pre>
final HashMap<String, String> buddies = new HashMap<String, String>();
...
private void discoverService() {
DnsSdTxtRecordListener txtListener = new DnsSdTxtRecordListener() {
@Override
/* Callback includes:
* fullDomain: full domain name: e.g "printer._ipp._tcp.local."
* record: TXT record dta as a map of key/value pairs.
* device: The device running the advertised service.
*/
public void onDnsSdTxtRecordAvailable(
String fullDomain, Map<String,String> record, WifiP2pDevice device) {
Log.d(TAG, "DnsSdTxtRecord available -" + record.toString());
buddies.put(device.deviceAddress, record.get("buddyname"));
}
};
...
}
</pre>
<p>To get the service information, create a {@link
android.net.wifi.p2p.WifiP2pManager.DnsSdServiceResponseListener}. This
receives the actual description and connection information. The previous code
snippet implemented a {@link java.util.Map} object to pair a device address with the buddy
name. The service response listener uses this to link the DNS record with the
corresponding service information. Once both
listeners are implemented, add them to the {@link
android.net.wifi.p2p.WifiP2pManager} using the {@link
android.net.wifi.p2p.WifiP2pManager#setDnsSdResponseListeners(WifiP2pManager.Channel,
WifiP2pManager.DnsSdServiceResponseListener,
WifiP2pManager.DnsSdTxtRecordListener) setDnsSdResponseListeners()} method.</p>
<pre>
private void discoverService() {
...
DnsSdServiceResponseListener servListener = new DnsSdServiceResponseListener() {
@Override
public void onDnsSdServiceAvailable(String instanceName, String registrationType,
WifiP2pDevice resourceType) {
// Update the device name with the human-friendly version from
// the DnsTxtRecord, assuming one arrived.
resourceType.deviceName = buddies
.containsKey(resourceType.deviceAddress) ? buddies
.get(resourceType.deviceAddress) : resourceType.deviceName;
// Add to the custom adapter defined specifically for showing
// wifi devices.
WiFiDirectServicesList fragment = (WiFiDirectServicesList) getFragmentManager()
.findFragmentById(R.id.frag_peerlist);
WiFiDevicesAdapter adapter = ((WiFiDevicesAdapter) fragment
.getListAdapter());
adapter.add(resourceType);
adapter.notifyDataSetChanged();
Log.d(TAG, "onBonjourServiceAvailable " + instanceName);
}
};
mManager.setDnsSdResponseListeners(channel, servListener, txtListener);
...
}
</pre>
<p>Now create a service request and call {@link
android.net.wifi.p2p.WifiP2pManager#addServiceRequest(WifiP2pManager.Channel,
WifiP2pServiceRequest, WifiP2pManager.ActionListener) addServiceRequest()}.
This method also takes a listener to report success or failure.</p>
<pre>
serviceRequest = WifiP2pDnsSdServiceRequest.newInstance();
mManager.addServiceRequest(channel,
serviceRequest,
new ActionListener() {
@Override
public void onSuccess() {
// Success!
}
@Override
public void onFailure(int code) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
}
});
</pre>
<p>Finally, make the call to {@link
android.net.wifi.p2p.WifiP2pManager#discoverServices(WifiP2pManager.Channel,
WifiP2pManager.ActionListener) discoverServices()}.</p>
<pre>
mManager.discoverServices(channel, new ActionListener() {
@Override
public void onSuccess() {
// Success!
}
@Override
public void onFailure(int code) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
if (code == WifiP2pManager.P2P_UNSUPPORTED) {
Log.d(TAG, "P2P isn't supported on this device.");
else if(...)
...
}
});
</pre>
<p>If all goes well, hooray, you're done! If you encounter problems, remember
that the asynchronous calls you've made take an
{@link android.net.wifi.p2p.WifiP2pManager.ActionListener} as an argument, and
this provides you with callbacks indicating success or failure. To diagnose
problems, put debugging code in {@link
android.net.wifi.p2p.WifiP2pManager.ActionListener#onFailure(int) onFailure()}. The error code
provided by the method hints at the problem. Here are the possible error values
and what they mean</p>
<dl>
<dt> {@link android.net.wifi.p2p.WifiP2pManager#P2P_UNSUPPORTED}</dt>
<dd> Wi-Fi P2P isn't supported on the device running the app.</dd>
<dt> {@link android.net.wifi.p2p.WifiP2pManager#BUSY}</dt>
<dd> The system is to busy to process the request.</dd>
<dt> {@link android.net.wifi.p2p.WifiP2pManager#ERROR}</dt>
<dd> The operation failed due to an internal error.</dd>
</dl>