【Android Developers Training】 76. 用Wi-Fi创建P2P连接

时间:2024-01-09 19:56:08

注:本文翻译自Google官方的Android Developers Training文档,译者技术一般,由于喜爱安卓而产生了翻译的念头,纯属个人兴趣爱好。

原文链接:http://developer.android.com/training/connect-devices-wirelessly/wifi-direct.html


Wi-Fi的P2P API允许设备连接到附近的设备,而不需要连接到网络或热点(Android的Wi-Fi P2P框架使用Wi-Fi Direct™认证程序来编译)Wi-Fi P2P允许你的应用快速发现并连接到附近的设备,这一功能比起蓝牙来说更加强大。

这节课将向你展示如何使用Wi-Fi P2P来发现并连接附近的设备。


一). 设置应用权限声明

为了使用Wi-Fi P2P,需要添加CHANGE_WIFI_STATEACCESS_WIFI_STATEINTERNET权限声明到你的清单文件中。Wi-Fi P2P不需要一个网络连接,但它使用了标准的Java套接字,而这需要INTERNET权限。所以你需要下列权限来使用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_WIFI_STATE"/>
<uses-permission
android:required="true"
android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission
android:required="true"
android:name="android.permission.INTERNET"/>
...

二). 配置一个广播接收器和一个P2P管理器

要使用Wi-Fi P2P,你需要监听在某一事件发生时,用来告知你的应用的广播Intents。在你的应用中,实例化一个IntentFilter并设置它为监听下列事件:

WIFI_P2P_STATE_CHANGED_ACTION

指出Wi-Fi P2P已经启用

WIFI_P2P_PEERS_CHANGED_ACTION

指出可以获得的peer列表发生了变化

WIFI_P2P_CONNECTION_CHANGED_ACTION

指出Wi-Fi P2P连接的状态发生了变化

WIFI_P2P_THIS_DEVICE_CHANGED_ACTION

指出设备的配置细节发生了改变

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); ...
}

onCreate()方法的最后,获取一个WifiP2pManager的实例,然后调用其initialize()方法。这一方法返回一个WifiP2pManager.Channel对象,在之后你将会用到它将你的应用连接到Wi-Fi P2P框架。

@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,来监听系统的Wi-Fi P2P状态的改变。在onReceive()方法中,添加一个条件分支来处理每一个之前列举出来的P2P状态变化。

    @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)); }
}

最后,添加一些代码,在主activity处于活动状态时,注册intent过滤器和广播接收器,并在activity被暂停时注销它们。做这两件事情最好的位置是在onResume()onPause()方法中。

    /** 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);

三). 初始化Peer搜索

要使用Wi-Fi P2P来搜索附近的设备,调用discoverPeers()方法。这一方法接收如下参数:

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.
}
});

记住这仅仅是初始化了peer搜索。discoverPeers()方法启动搜索进程,然后迅速返回。系统会通知你搜索进程是否被监听器初始化成功。同时搜索会保持激活状态知道一个连接被初始化或者一个P2P组被构建完成。


四). 获取Peers列表

现在写下获取和处理Peers列表的代码。首先实现WifiP2pManager.PeerListListener接口,它提供了检测到的Wi-Fi P2P的peer信息。请看下面的代码:

    private List peers = new ArrayList();
... private PeerListListener peerListListener = new PeerListListener() {
@Override
public void onPeersAvailable(WifiP2pDeviceList peerList) { // 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 of available
// 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,当一个具有WIFI_P2P_PEERS_CHANGED_ACTION的intent被接收时,来调用requestPeers()方法。你需要通过某种方法将监听器传递给广播接收器。一种方法是将它作为一个参数传递给广播接收器的构造函数:

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");
}...
}

现在,一个具有WIFI_P2P_PEERS_CHANGED_ACTION的intent将会激活一个更新Peer列表的请求。


五). 与一个Peer发起连接

为了和一个Peer发起连接,创建一个新的WifiP2pConfig对象,然后从代表你想要连接的设备的WifiP2pDevice中把数据拷贝到这个对象里面。然后调用connect()方法。

    @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();
}
});
}

在这个代码中实现的WifiP2pManager.ActionListener仅在当初始化成功或失败时向你发起通知。要监听连接状态的变化,需要实现WifiP2pManager.ConnectionInfoListener接口。它的onConnectionInfoAvailable()回调函数将会在连接状态变化后向你发出通知。在一些情况下,许多设备会向一个设备发起连接(比如一个多人连接的游戏,或者一个聊天的应用),其中一个设备会被任命为一个“组所有者(group owner)”。

    @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.
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.
}
}

现在回到广播接收器的onReceive()方法中,修改监听WIFI_P2P_CONNECTION_CHANGED_ACTION的intent的部分。当这个intent接收到了以后,调用requestConnectionInfo()。这是一个异步的调用,所以结果会被之前你所提供的作为参数的连接信息监听器接收:

        ...
} 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);
}
...