本文译自:http://developer.android.com/training/connect-devices-wirelessly/wifi-direct.html
WiFi对等API(P2P)不需要连接到网络或热点(Android的WiFi P2P框架符合WiFi编程指导规范),就允许应用程序连接到附近的设备。WiFiP2P允许应用程序快速的查找附近的设备,并与其交互。在连接范围上超过了蓝牙的能力。
本文介绍如何使用WiFi P2P来查找和连接附近的设备。
建立应用程序权限
为了使用WiFi P2P,要在应用程序的清单文件中添加CHANGE_WIFI_STATE、ACCESS_WIFI_STATE和INTERNET权限。WiFi P2P不要求互联网连接,但是它使用标准的Java套接字,它要求INTERNET权限。因此使用WiFi P2P需要下例权限。
<manifestxmlns: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"/>
...
建立广播接收器和对等管理器
要使用WiFi P2P,就要监听广播意图,在确定事件发生时,告诉你的应用程序。在你的应用程序中,要实例化一个IntentFilter对象,并设置它来监听以下动作:
指示是否启用WiFi P2P。
指示可用的对等列表已经发生了改变。
WIFI_P2P_CONNECTION_CHANGED_ACTION
指示WiFi P2P连接的状态已经发生改变。
WIFI_P2P_THIS_DEVICE_CHANGED_ACTION
指示设备的配置明细已经发生改变。
privatefinalIntentFilterintentFilter =newIntentFilter();
...
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Indicates achange in the Wi-Fi P2P status.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
// Indicates a change inthe list of available peers.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
// Indicates the state ofWi-Fi P2P connectivity has changed.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
// Indicates this device'sdetails have changed.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
...
}
在onCreate()方法中,获取一个WifiP2pManager对象的实例,并调用它的initialize()方法。这个方法会返回一个WifiP2pManager.Channel对象,它会用于后续对WiFi P2P框架的连接。
@Override
Channel mChannel;
public void onCreate(Bundle savedInstanceState) {
....
mManager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
mChannel = mManager.initialize(this, getMainLooper(), null);
}
现在创建一个新的BroadcastReceiver类,用于监听系统的WiFi P2P状态的改变。在onReceive()方法中,添加处理上述每个P2P状态改变的条件。
@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 somethingabout
// that.
} else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {
// Connection state changed! We should probably do somethingabout
// 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));
}
}
最后,在你的主Activity激活时,添加注册Intent过滤器和广播接收器的代码,并在Activity被挂起时,解除注册。做这件事的最好的地方是onResume()和onPause()方法
/** register the BroadcastReceiverwith 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);
}
启动对等点发现功能
要使用Wi-Fi P2P来搜索附近的设备,就要调用discoverPeers()方法,这个方法需要以下参数:
WifiP2pManager.Channel:这个参数是在初始化对等管理器时获取,用于把应用程序连接到Wi-Fi的P2P框架中;
WifiP2pManager.ActionListener接口实现:系统会在处理成功或失败时调用该接口中对应的方法。
mManager.discoverPeers(mChannel,newWifiP2pManager.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.
}
});
记住,这只是启动对等点发现功能。DiscoverPeers()方法启动发现处理,然后立即返回。系统会通过调用你传入的第二参数中的对应的接口方法,通知你对等点发现处理是否启动成功。此外,发现处理会一直保持到连接被启动或P2P组被组建。
获取对等点的列表
现在要编写获取和处理对等点列表的代码。首先实现WifiP2pManager.PeerListener接口,这个接口会提供有关已经发现的Wi-Fi的P2P对等点的信息。下列代码演示这个处理:
privateList peers =newArrayList();
...
private PeerListListenerpeerListListener = new PeerListListener() {
@Override
public void onPeersAvailable(WifiP2pDeviceListpeerList) {
// Out with the old, in with the new.
peers.clear();
peers.addAll(peerList.getDeviceList());
// If an AdapterView is backed by this data, notify it
// of the change. For instance, if you have a ListView ofavailable
// peers, trigger an update.
((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged();
if (peers.size() == 0) {
Log.d(WiFiDirectActivity.TAG, "No devices found");
return;
}
}
}
现在,修改你的广播接收器的onReceive()方法,当接收到带有WIFI_P2P_PEERS_CHANGED_ACTION操作的Intent时,调用requestPeers()方法,并把上面实现的监听器传递给requestPeers()方法。你可以把这个监听器作为广播接收器的构造器的参数来传递。
publicvoid onReceive(Context context,Intent intent){
...
else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {
// Requestavailable peers from the wifi p2p manager. This is an
//asynchronous call and the calling activity is notified with a
// callbackon PeerListListener.onPeersAvailable()
if (mManager != null) {
mManager.requestPeers(mChannel,peerListListener);
}
Log.d(WiFiDirectActivity.TAG, "P2P peerschanged");
}...
}
这样,带有WIFI-P2P_PEERS_CHANGED_ACTION的Intent操作就会触发更新对等点列表的请求。
连接到对等点
为了连接到对等点,要创建一个新的WifiP2pConfig对象,并从代表你要连接的设备的WifiP2pDevice对象中复制数据到这个WifiP2pConfig对象中。然后调用connect()方法。
@Override
public void connect() {
// Pickingthe 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();
}
});
}
上述实现的WifiP2pManager.ActionListener接口只会通知你连接成功还是失败。要监听连接状态的变化,就好实现WifiP2pManager.ConnectionInfoListener()接口,这个接口中的onConnectionInfoAvailable()回调方法在连接状态变化时通知你。当有多个设备连接一个设备时,其中一个设备将会被指定为“组管理者”。
@Override
public voidonConnectionInfoAvailable(final WifiP2pInfo info) {
//InetAddress from WifiP2pInfo struct.
InetAddress groupOwnerAddress =info.groupOwnerAddress.getHostAddress());
// After thegroup negotiation, we can determine the group owner.
if (info.groupFormed && info.isGroupOwner) {
// Do whatever tasks are specific to the group owner.
// One common case is creating a server thread and accepting
// incoming connections.
} else if (info.groupFormed) {
// The other device acts as the client. In this case,
// you'll want to create a client thread that connects to the group
// owner.
}
}
现在,返回到广播接收器的onReceive()方法,修改对WIFI_P2P_CONNECTION_CHANGED_ACTION的Intent操作的监听。当收到这个Intent时,调用requestConnectionInfo()方法。这是一个异步调用,因此,结果会被你提供的连接信息监听器接收到。
...
} 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);
}
...