Question

我正在考虑通过多个Android设备之间的Wi-Fi Direct连接进行广播的可能性。我创建了一个简单的消息广播应用程序来测试它是否有效，但到目前为止我还没有能够广播消息。当我尝试发送数据包时，我得到 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

这是我的代码的本质：

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);
}

This post建议通过Wi-Fi Direct进行广播。

是否有人知道 Android 设备上的Wi-Fi Direct广播是否真的有效？如果它应该有效，我做错了什么？

我开始认为这些设备不知道在哪里路由广播数据包。在我的情况下，它需要工作，而无需root设备并手动添加广播数据包的路由。

更新

使用 Romain Hippeau 建议的getBroadcastAddress()函数后，SocketException消失了，看起来广播正在按预期工作。但是，我在第二台设备上收到广播时遇到了问题。

我正在使用以下代码接收广播：

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();
}

我还尝试通过添加DatagramSocket作为参数为InetAddress.getByName("0.0.0.0")添加通配符地址，但没有运气。

建议？

Answer 1

从https://code.google.com/p/boxeeremote/wiki/AndroidUDP

无耻地被盗

尝试以这种方式获取网络连接：

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);
}

然后尝试以这种方式发送数据包：

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：从同一页面阅读试试这个......

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，您需要以下权限才能使用：
＆lt; uses-permission android：name =“android.permission.CHANGE_WIFI_MULTICAST_STATE”/＆gt;

通过Wi-Fi Direct进行广播

1 个答案: