运行在局域网上的UDP服务器

Question

我正在使用UDP服务器，但我的服务器类给我错误，我使用服务类为我的服务器和创建线程，但最终它没有运行，并给我错误，它会停止后运行几秒钟。

public class MainActivity extends Service { 


static String UDP_BROADCAST = "UDPBroadcast"; 
DatagramSocket socket; 


private void listenAndWaitAndThrowIntent(InetAddress broadcastIP, Integer port) throws Exception { 
    byte[] recvBuf = new byte[15000]; 
    if (socket == null || socket.isClosed()) 
    { 
     socket = new DatagramSocket(port, broadcastIP); 
     socket.setBroadcast(true); 
    } 
    DatagramPacket packet = new DatagramPacket(recvBuf, recvBuf.length); 
    Log.e("UDP", "Waiting for UDP broadcast"); 
    socket.receive(packet); 

    String senderIP = packet.getAddress().getHostAddress(); 
    String message = new String(packet.getData()).trim(); 
    Log.e("UDP", "Got UDB broadcast from " + senderIP + ", message: " + message); 

// broadcastIntent(senderIP, message); 
    socket.close(); 
} 
private void broadcastIntent(String senderIP, String message) { 
    Intent intent = new Intent(MainActivity.UDP_BROADCAST); 
    intent.putExtra("sender", senderIP); 
    intent.putExtra("message", message); 
    sendBroadcast(intent); 
} 
    Thread UDPBroadcastThread; 

void startListenForUDPBroadcast() { 
    UDPBroadcastThread = new Thread(new Runnable() { 
     public void run() { 
      try { 
       InetAddress broadcastIP =  InetAddress.getByName("192.168.1.101"); //172.16.238.42 //192.168.1.255 
       Integer port = 11111; 
       while (shouldRestartSocketListen) { 
        listenAndWaitAndThrowIntent(broadcastIP, port); 
       } 
       //if (!shouldListenForUDPBroadcast) throw new ThreadDeath(); 
      } catch (Exception e) { 
       Log.i("UDP", "no longer listening for UDP broadcasts cause of error " + e.getMessage()); 
      } 
     } 
    }); 
    UDPBroadcastThread.start(); 
} 
      private Boolean shouldRestartSocketListen=true; 

void stopListen() { 
    shouldRestartSocketListen = false; 
    socket.close(); 
} 

@Override 
public void onCreate() { 

}; 

@Override 
public void onDestroy() { 
    stopListen(); 
} 


@Override 
public int onStartCommand(Intent intent, int flags, int startId) { 
    shouldRestartSocketListen = true; 
    startListenForUDPBroadcast(); 
    Log.i("UDP", "Service started"); 
    return START_STICKY; 
} 

@Override 
public IBinder onBind(Intent intent) { 
    return null; 
} 
} 

我的日志猫：

08-26 19:28:44.232: D/AndroidRuntime(618): Shutting down VM 
    08-26 19:28:44.252: W/dalvikvm(618): threadid=1: thread exiting with uncaught exception (group=0x409961f8) 
    08-26 19:28:44.352: E/AndroidRuntime(618): FATAL EXCEPTION: main 
    08-26 19:28:44.352: E/AndroidRuntime(618): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.receiver/com.example.receiver.MainActivity}: java.lang.ClassCastException: com.example.receiver.MainActivity cannot be cast to android.app.Activity 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1879) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.app.ActivityThread.access$600(ActivityThread.java:122) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.os.Handler.dispatchMessage(Handler.java:99) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.os.Looper.loop(Looper.java:137) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.app.ActivityThread.main(ActivityThread.java:4340) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at java.lang.reflect.Method.invokeNative(Native Method) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at java.lang.reflect.Method.invoke(Method.java:511) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at dalvik.system.NativeStart.main(Native Method) 
    08-26 19:28:44.352: E/AndroidRuntime(618): Caused by: java.lang.ClassCastException: com.example.receiver.MainActivity cannot be cast to android.app.Activity 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.app.Instrumentation.newActivity(Instrumentation.java:1023) 
    08-26 19:28:44.352: E/AndroidRuntime(618): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1870) 
    08-26 19:28:44.352: E/AndroidRuntime(618): ... 11 more 

Answer 1

你混合不同的任务，你想在这里做。您的活动必须延长Activity才能使Android能够在屏幕上显示它。另一方面，Service基本上是告诉Android您有一些背景或点播任务需要照顾的方式。

您需要从Service中分离出您的用户界面（它需要是Activity）。根据您的代码，看起来您的班级中实际上没有任何名为MainActivity的UI代码，因此您需要编写一个代码（其中扩展了Activity），或者将您的意图指向您现有的Activity。您还应该重命名MainActivity，因为它实际上不是Activity。

Android documentation for Service有一些可能有用的示例。