广播通过Wi-Fi直(Broadcasting over Wi-Fi Direct)

我看可能性广播在多个Android设备之间的Wi-Fi直连连接。我创建了一个简单的消息广播应用程序来测试它是否工作正常，但到目前为止，我还没有能够播出的消息。当我尝试发送数据包我接收到一个SocketException（网络无法访问）：

03-20 13:23:00.148: E/UdpBroadcaster(4180): sendto failed: ENETUNREACH (Network is unreachable)
03-20 13:23:00.148: E/UdpBroadcaster(4180): java.net.SocketException: sendto failed: ENETUNREACH (Network is unreachable)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at libcore.io.IoBridge.maybeThrowAfterSendto(IoBridge.java:496)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at libcore.io.IoBridge.sendto(IoBridge.java:465)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at java.net.PlainDatagramSocketImpl.send(PlainDatagramSocketImpl.java:182)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at java.net.DatagramSocket.send(DatagramSocket.java:307)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at com.example.android.wifidirect.UdpBroadcaster.sendMessage(UdpBroadcaster.java:59)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at com.example.android.wifidirect.UdpBroadcaster.run(UdpBroadcaster.java:44)
03-20 13:23:00.148: E/UdpBroadcaster(4180): Caused by: libcore.io.ErrnoException: sendto failed: ENETUNREACH (Network is unreachable)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at libcore.io.Posix.sendtoBytes(Native Method)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at libcore.io.Posix.sendto(Posix.java:146)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at libcore.io.BlockGuardOs.sendto(BlockGuardOs.java:177)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     at libcore.io.IoBridge.sendto(IoBridge.java:463)
03-20 13:23:00.148: E/UdpBroadcaster(4180):     ... 4 more

这是我的代码的精髓：

InetAddress broadcastAddress = InetAddress.getByName("255.255.255.255");
int port = 8888;

DatagramSocket socket = new DatagramSocket(port);
socket.setBroadcast(true);
socket.connect(broadcastAddress, port);

String message = "Hello";
byte[] buffer = message.getBytes();

DatagramPacket packet = new DatagramPacket(
        buffer, buffer.length, broadcastAddress, port);

try {
    socket.send(packet); // <----- Causes a SocketException
} catch (IOException e) {
    Log.e(TAG, e.getMessage(), e);
}

这篇文章表明，广播通过Wi-Fi直应该是可能的。

有谁知道广播在Wi-Fi直接在Android设备上是否实际工作？如果它应该工作，我究竟做错了什么？

我开始觉得设备不知道从哪里路由广播包。在我的情况需要，而不必以root设备和手动添加一个路由，广播包的工作。

更新

使用后getBroadcastAddress() 罗曼Hippeau建议功能SocketException消失了，好像在广播如预期运行。然而，我在接收所述第二设备上的广播的问题。

我使用下面的代码接收广播：

DatagramSocket socket = null;
try {
    socket = new DatagramSocket(8888);
    socket.setBroadcast(true); // Not needed?
    socket.setSoTimeout(200);

    DatagramPacket packet = null;
    while (!mStopping) {
        byte[] buffer = new byte[1024];
        packet = new DatagramPacket(buffer, buffer.length);

        try {
            socket.receive(packet);

            if (packet.getData().length > 0) {
                String receivedString = new String(packet.getData());

                Log.i(TAG, "Received string: " + receivedString);
            }
        } catch (InterruptedIOException e) { /* Ignore */ }
    }
} catch (IOException e) {
    Log.e(TAG, e.getMessage(), e);
} finally {
    if (socket != null)
        socket.close();
}

我也试图通配符地址添加到DatagramSocket加入InetAddress.getByName("0.0.0.0")作为参数，但没有运气。

建议？

从无耻地窃取https://code.google.com/p/boxeeremote/wiki/AndroidUDP

尝试让您的网络连接是这样的：

InetAddress getBroadcastAddress() throws IOException {
    WifiManager wifi = mContext.getSystemService(Context.WIFI_SERVICE);
    DhcpInfo dhcp = wifi.getDhcpInfo();
    // handle null somehow

    int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
    byte[] quads = new byte[4];
    for (int k = 0; k < 4; k++)
      quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
    return InetAddress.getByAddress(quads);
}

然后尝试发送一个数据包是这样的：

DatagramSocket socket = new DatagramSocket(PORT);
socket.setBroadcast(true);
DatagramPacket packet = new DatagramPacket(data.getBytes(), data.length(),
    getBroadcastAddress(), PORT);
socket.send(packet);

// If you want to listen for a response ...
byte[] buf = new byte[1024];
DatagramPacket packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);

编辑：从同一个页面读取试试这个...

WifiManager wifi = (WifiManager) this.getSystemService(Context.WIFI_SERVICE);
MulticastLock lock = wifi.createMulticastLock("dk.aboaya.pingpong");
lock.acquire();
serverSocket = new DatagramSocket(19876);
serverSocket.setSoTimeout(15000); //15 sec wait for the client to connect
byte[] data = new byte[UDPBatPositionUpdater.secretWord.length()]; 
DatagramPacket packet = new DatagramPacket(data, data.length);
serverSocket.receive(packet);
lock.release();
String s = new String(packet.getData());
System.out.println(s);

请记住，你需要下列权限为它工作：
<使用的许可机器人：名称= “android.permission.CHANGE_WIFI_MULTICAST_STATE”/>