java - 为什么我的简单应用程序没有收到 UDP 数据包

Question

这个问题在这里已经有了答案:





How can I fix 'android.os.NetworkOnMainThreadException'?

(66 个回答)


6年前关闭。




我正在尝试创建一个简单的应用程序，它将接收来自 WiFi 模块的 UDP 数据包。 WiFi模块每5秒发送一个数据包，但我一直无法成功接收。

使用 toasts 作为调试的一种方式，我以正确的顺序收到它们，直到“这里也没有得到它”，这告诉我问题出在 'socket.receive(packet)' 行。

有没有人知道为什么它可能不起作用？我还通过在线查看大量问题/示例尝试了代码的变体，但它们仍然会导致“socket.receive(packet)”行出现问题。

另外，我写了一个python脚本来做同样的事情，在同一个端口上寻找UDP数据包，并用QPython运行它，它确实收到了数据包，所以看起来数据包是由WiFi模块发送的，并且接收到了通过平板电脑，只是应用程序由于某种原因不会读取数据。

任何帮助或见解将不胜感激，谢谢。

这是代码:

public void run() {

    Toast.makeText(this, "RIGHT BEFORE TRY", Toast.LENGTH_LONG).show();

    DatagramSocket socket;
    DatagramPacket packet;


   try {
        Toast.makeText(this, "IN THE TRY", Toast.LENGTH _LONG).show();
        socket = new DatagramSocket(9750);
        byte[] buf = new byte[1024]; //buffer
        socket.setSoTimeout(100000);
        Toast.makeText(this, "Timeout is: " + socket.getSoTimeout(), Toast.LENGTH_LONG).show();
        //DatagramPacket packet = new DatagaramPacket(buf, buf.length);
        //Toast.makeText(this, "PACKET SIZE IS: "+buf.length, Toast.LENGTH_LONG).show();

        // while(true) {
        Toast.makeText(this, "IN THE WILD!", Toast.LENGTH_LONG).show();
        packet = new DatagramPacket(buf, buf.length);
        Toast.makeText(this, "PACKET SIZE IS: " + buf.length, Toast.LENGTH_LONG).show();

        try {
            //socket.receive(packet);
            socket.receive(packet);
            Toast.makeText(this, "GOT SOMETHING!", Toast.LENGTH_LONG).show();
        }
        catch (Exception i) {
            // TODO Auto-generated catch block
            //i.printStackTrace();
            Toast.makeText(this, "DIDN'T GET IT HERE EITHER!", Toast.LENGTH_LONG).show();
        }
        //byte[] result = new byte[packet.getLength()];
        byte[] result = packet.getData();
        System.arraycopy(packet.getData(), 0, result, 0, packet.getLength());
        String msg = new String(result);
        Toast.makeText(this, msg, Toast.LENGTH_LONG).show();
        Toast.makeText(this, "END WHILE!", Toast.LENGTH_LONG).show();
        //}

    } catch (Exception e) {
        // TODO Auto-generated catch block
        //e.printStackTrace();
        Toast.makeText(this, "DIDN'T GET IT!", Toast.LENGTH_LONG).show();

    }

}

更新:在前两个答案之后，看起来我们试图在主线程中进行网络操作，这是不可行的，所以我们目前正在尝试用另一个线程或异步任务来实现它。希望有一些好消息:)

Answer 1

正如您所说，有 NetworkOnMainThread 异常，您只需将此问题放在新线程上并启动它...

Thread thread = new Thread() {
    @Override
    public void run() {
Toast.makeText(this, "RIGHT BEFORE TRY", Toast.LENGTH_LONG).show();

    DatagramSocket socket;
    DatagramPacket packet;


   try {
        Toast.makeText(this, "IN THE TRY", Toast.LENGTH _LONG).show();
        socket = new DatagramSocket(9750);
        byte[] buf = new byte[1024]; //buffer
        socket.setSoTimeout(100000);
        Toast.makeText(this, "Timeout is: " + socket.getSoTimeout(), Toast.LENGTH_LONG).show();
        //DatagramPacket packet = new DatagaramPacket(buf, buf.length);
        //Toast.makeText(this, "PACKET SIZE IS: "+buf.length, Toast.LENGTH_LONG).show();

        // while(true) {
        Toast.makeText(this, "IN THE WILD!", Toast.LENGTH_LONG).show();
        packet = new DatagramPacket(buf, buf.length);
        Toast.makeText(this, "PACKET SIZE IS: " + buf.length, Toast.LENGTH_LONG).show();

        try {
            //socket.receive(packet);
            socket.receive(packet);
            Toast.makeText(this, "GOT SOMETHING!", Toast.LENGTH_LONG).show();
        }
        catch (Exception i) {
            // TODO Auto-generated catch block
            //i.printStackTrace();
            Toast.makeText(this, "DIDN'T GET IT HERE EITHER!", Toast.LENGTH_LONG).show();
        }
        //byte[] result = new byte[packet.getLength()];
        byte[] result = packet.getData();
        System.arraycopy(packet.getData(), 0, result, 0, packet.getLength());
        String msg = new String(result);
        Toast.makeText(this, msg, Toast.LENGTH_LONG).show();
        Toast.makeText(this, "END WHILE!", Toast.LENGTH_LONG).show();
        //}

    } catch (Exception e) {
        // TODO Auto-generated catch block
        //e.printStackTrace();
        Toast.makeText(this, "DIDN'T GET IT!", Toast.LENGTH_LONG).show();

    }


    }
};
thread.start();