java - TCP server on android phone crashes at .accept()

itemprop="text">

I'm new to android but not to sockets.
I have a GUI with a button that runs the UAVServer thread. When I click it, the server
should listen for the client. The line of
code...

Socket client =
            serverSocket.accept();

...Should
block until a client connects. But it just crashes saying "Unfortunately, DroidUAV has
stopped."

public class
            UAVServer extends Thread {

 private String TAG =
            UAVServer.class.getSimpleName(); 

 @Override
 public void
            run() { 
 ServerSocket serverSocket;
 try {
 serverSocket
            = new ServerSocket(12345); 
 Log.d(TAG, "Fails at the next line of
            code");

 Socket client = serverSocket.accept();
 } catch
            (IOException e) {
 // TODO Auto-generated catch block

            e.printStackTrace();
 } 

            }
}

This
seems pretty straight forward, why would it be crashing? Also how does android handle
blocking ports, this might have something to do with it. If it was on the wifi, I figure
it would be up to the router to unblock ports. But what if I was just on
4G?

NOTE: uses-permission
android:name="android.permission.INTERNET"
is in my manifest
file.

Edit:
I must be doing something
wrong, because I just tried to make it run the client instead and it crashes on this
line...

Socket s = new
            Socket("192.168.1.102",4444);

Edit:
Added
errors...

FATAL EXCEPTION:
            main
java.lang.IllegalStateException: Could not execute method of the
            activity
 at android.view.View$1.onClick(View.java:3071)
 at
            android.view.View.performClick(View.java:3538)
 at
            android.widget.CompoundButton.performClick(CompoundButton.java:103)
 at
            android.view.View$PerformClick.run(View.java:14319)
 at
            android.os.Handler.handleCallback(Handler.java:608)

 at
            android.os.Handler.dispatchMessage(Handler.java:92)
 at
            android.os.Looper.loop(Looper.java:156)
 at
            android.app.ActivityThread.main(ActivityThread.java:5099)
 at
            java.lang.reflect.Method.invokeNative(Native Method)
 at
            java.lang.reflect.Method.invoke(Method.java:511)
 at
            com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:991)

            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:758)
 at
            dalvik.system.NativeStart.main(Native Method)
Caused by:
            java.lang.reflect.InvocationTargetException
 at
            java.lang.reflect.Method.invokeNative(Native Method)

 at
            java.lang.reflect.Method.invoke(Method.java:511)
 at
            android.view.View$1.onClick(View.java:3066)
 ... 12 more
Caused by:
            android.os.NetworkOnMainThreadException
 at
            android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1190)

            at libcore.io.BlockGuardOs.accept(BlockGuardOs.java:54)
 at
            java.net.PlainSocketImpl.accept(PlainSocketImpl.java:98)
 at
            java.net.ServerSocket.implAccept(ServerSocket.java:202)
 at
            java.net.ServerSocket.accept(ServerSocket.java:127)
 at
            com.example.droiduav.UAVServer.run(UAVServer.java:19)

 at
            com.example.droiduav.MainActivity.onToggleServer(MainActivity.java:31)
 ... 15
            more

class="post-text" itemprop="text">

class="normal">Answer

Well, the
problem you are facing has to do with the following exception that can be seen in your
LogCat trace:

Caused by:
android.os.NetworkOnMainThreadException

What
it means is pretty straightforward guessable from the name. Don't perform any Network
code on the Main UI Thread. Solution: href="http://developer.android.com/training/basics/network-ops/connecting.html#AsyncTask"
rel="nofollow noreferrer">Start your own thread for that (see href="http://developer.android.com/training/basics/network-ops/connecting.html#AsyncTask"
rel="nofollow noreferrer">this Android Developer
article).

Why?

Network
code can take a "long time" (assume several seconds) to execute. If you would call all
your network code on the main thread, it will freeze the UI in the mean time (this is -
as one could guess - not really preferable and could and will result in href="http://developer.android.com/training/articles/perf-anr.html" rel="nofollow
noreferrer">ANR exceptions).

see
also these questions as they are related to your
problem: