Android socket client doesn't work

Question

I try to create a socket client connection to a python server like this, but it throwss me an error. This is triggered via a button, which works. The server is running on a RPi, but that's not the problem since a Python client works on my PC.

try {

        Socket s = new Socket("192.168.178.43", 24069);
        InputStreamReader streamReader = new InputStreamReader(s.getInputStream());
        BufferedReader reader = new BufferedReader(streamReader);

        String advice = reader.readLine();
        reader.close();

    } catch (UnknownHostException e) {
        System.err.println("Unknown Host.");
        // System.exit(1);
    } catch (IOException e) {
        System.err.println("Couldn't get I/O for "
                + "the connection.");
        System.err.println(e);
        //  System.exit(1);
    }

Stacktrace:

    java.lang.IllegalStateException: Could not execute method of the activity
            at android.view.View$1.onClick(View.java:3823)
            at android.view.View.performClick(View.java:4438)
            at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            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:515)
            at android.view.View$1.onClick(View.java:3818)
            at android.view.View.performClick(View.java:4438)
            at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: android.os.NetworkOnMainThreadException
            at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145)
            at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84)
            at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
            at libcore.io.IoBridge.connect(IoBridge.java:112)
            at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
            at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
            at java.net.Socket.startupSocket(Socket.java:567)
            at java.net.Socket.tryAllAddresses(Socket.java:128)
            at java.net.Socket.<init>(Socket.java:178)
            at java.net.Socket.<init>(Socket.java:150)
            at com.example.app.MainActivity.sendMessage(MainActivity.java:65)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at android.view.View$1.onClick(View.java:3818)
            at android.view.View.performClick(View.java:4438)
at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

"Caused by: android.os.NetworkOnMainThreadException" You can't perform network operations on the main (UI) thread. You'll need to run your code on a separate thread - use an AsyncTask, IntentService or some other way of creating a different thread. — Squonk
– Squonk, Commented Mar 23, 2014 at 23:44

Antwan · Accepted Answer · 2014-03-23 23:58:12Z

you can't do any long time process on the Main UI thread the reason for that to avoid the crash of your App if your operation failed

try to create new thread and do your work inside of it and if u want to pass any result to the UI u cant use

View.Post()

or

 context.runOnUiThread()

this is an example of what you can do or you can use asynctask instead

new Thread(new Runnable() {
        public void run() {
           try {

        Socket s = new Socket("192.168.178.43", 24069);
        InputStreamReader streamReader = new InputStreamReader(s.getInputStream());
        BufferedReader reader = new BufferedReader(streamReader);

        String advice = reader.readLine();
        reader.close();

    } catch (UnknownHostException e) {
        System.err.println("Unknown Host.");
        // System.exit(1);
    } catch (IOException e) {
        System.err.println("Couldn't get I/O for "
                + "the connection.");
        System.err.println(e);
        //  System.exit(1);
    }

        }
    }).start();

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