Connecting with Wi-Fi Direct

Connecting with Wi-Fi Direct

     Wi-Fi Direct™ APIs允许应用连接周围的设备，而不用通过网络或者热点，点对点直接连接。应用可以快速的发现周围设备并与之交互，而有效作用距离大于蓝牙。

     以下内容关于如何通过Wi-Fi Direct™发现和连接周围设备：

第一步：权限问题 Set Up Application Permissions

在manifest里添加三个权限：

CHANGE_WIFI_STATE,

ACCESS_WIFI_STATE,

INTERNET 。

Wi-Fi Direct™不需要网络，但是需要java socket，而java socket需要INTERNET 权限。

<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"/>

    ...

第二步：新建广播接收器和点对点管理器

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

     使用Wi-Fi Direct™，需要监听（broadcast intents）广播intent，当有特定的事件发生时，你的应用就会觉察到。

在app里实例化一个IntentFilter对象出来，将其设置为监听以下内容：

WIFI_P2P_STATE_CHANGED_ACTION
Indicates whether Wi-Fi Peer-To-Peer (P2P) is enabled----P2P功能是否打开
WIFI_P2P_PEERS_CHANGED_ACTION
Indicates that the available peer list has changed.----可连接peer改变
WIFI_P2P_CONNECTION_CHANGED_ACTION
Indicates the state of Wi-Fi P2P connectivity has changed.----P2P连接状态改变
WIFI_P2P_THIS_DEVICE_CHANGED_ACTION
Indicates this device's configuration details have changed.----设备设置改变

private final IntentFilterintentFilter = new IntentFilter();
...
@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    //  Indicates a change in the Wi-Fi Peer-to-Peer 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);

    ...
}

     在onCreate()方法最后，取得一个WifiP2pManager实例，调用它的initialize()方法，这个方法返回一个WifiP2pManager.Channel对象，这个后面用来连接app和Wi-Fi Direct Framework。

@Override

Channel mChannel;

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

     创建一个新的 BroadcastReceiver类，用来监听系统Wi-Fi P2P的变化状态，在 onReceive()方法里，增加condition条件来处理各种P2P状态的改变。

@Override
public void onReceive(Context context, Intent intent) {

        String action = intent.getAction();     //获取接收的intent里的action

        //以下进行判断，对各种不同的P2P状态改变，执行不同的代码
     if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
            // 检查 Wifi Direct模式是否开启
            int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
     if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) {
                activity.setIsWifiP2pEnabled(true);   //开启则...
            } else {
                activity.setIsWifiP2pEnabled(false);   //未开启则...
            }
        }

     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，当你 主activity 激活以后，添加代码在onResume()方法里注册 intent filter 和 broadcast receiver 。当你的activity paused的时候，在onPause()方法里对它们解除注册。

    @Override

    public void onResume() {
        super.onResume();
        receiver = new WiFiDirectBroadcastReceiver(mManager, mChannel, this);
        registerReceiver(receiver, intentFilter);
    }

    @Override
    public void onPause() {
        super.onPause();      //调用父类方法
        unregisterReceiver(receiver);   //添加新的内容，解除注册
    }

第三步：开始peer发现   Initiate Peer Discovery

调用discoverPeers()方法，来发现周围的设备。这个方法需要2个参数：

1. WifiP2pManager.Channel

2. WifiP2pManager.ActionListener 的一个新的实现

第一个参数是一个对象，第二个参数是内部类对象

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.
        }
});

这只是启动peer discovery，方法discoverPeers()开始了发现线程，然后马上返回。如果peer discovery线程成功启动，系统就会注意到。发现一直持续直到建立连接或者建立一个P2P group。



第四步：获取peer 列表 Fetch the List of Peers

首先实现WifiP2pManager.PeerListListener接口，这个接口提供了发现的peer的信息。

   private List peers = new ArrayList(); //装peer的list
    ...

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

            // Out with the old, in with the new.
            peers.clear();   //清空list，刷新
            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();

            //如果peers.size()=0，则没有发现peer
            if (peers.size() == 0) {
                Log.d(WiFiDirectActivity.TAG, "No devices found");
                return;
            }
        }
    }



修改broadcast receiver的onReceive()方法，当接收到一个action包含WIFI_P2P_PEERS_CHANGED_ACTION的Intent的时候，调用requestPeers()方法，

需要把监听器传入接收器，方法之一就是把listener传入broadcast receiver构造器。



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, peerListener);
        }
        Log.d(WiFiDirectActivity.TAG, "P2P peers changed");
    }...
}

    这样的话，一个intent的action是 WIFI_P2P_PEERS_CHANGED_ACTION 的时候，就会触发更新peer list的请求。

第五步：连接peer：Connect to a Peer

     要连接peer，就要new一个新的 WifiP2pConfig对象，并把想连接的peer的信息写入，最后调用 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();
            }
        });
    }

     WifiP2pManager.ActionListener只是负责通知peer initiation是否成功，要监听P2P状态改变的话，就要实现WifiP2pManager.ConnectionInfoListener，它的onConnectionInfoAvailable()回调方法会在P2P状态改变时做出反应。在多个设备需要连接同一个设备的情况下，有一个设备会被指定为“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.

        }

    }

返回到 broadcast receiver里的 onReceive()方法，修改下， 接收到WIFI_P2P_CONNECTION_CHANGED_ACTION 这个intent的时候，调用requestConnectionInfo()方法。

..

        } 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);

            }

From: http://blog.sina.com.cn/s/blog_819100560101a86s.html
LINUX\android\development\samples\WiFiDirectDemo
android 4.4 下 相关的p2p代码在frameworks/base/wifi/java/android/net/wifi/p2p/