Java code wont work in android studio. Port communication

Question

This code works fine in eclipse but when i try to run it in android studio i get an error. i'm new to learning java and don't know how to debug this. The error happens when creating a new socket but it works fine in eclipse.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //Host IP.
    String hostName = "192.168.0.3";
    //Port Number.
    int portNumber = 6666;
    try (
        //Create a connection with IP on selected port.
        Socket echoSocket = new Socket(hostName, portNumber);
        //Create an outputStream with the connection.
        PrintWriter out = new PrintWriter(echoSocket.getOutputStream(), true);
    ) {
        //Send data out the outputStream to server.
        out.println("Hello");
        //Exit so server knows to wait for the next connection.
        System.exit(1);
        //Catch Exceptions
    } catch (UnknownHostException e) {
        System.err.println("Don't know about host " + hostName);
        System.exit(1);
    } catch (IOException e) {
        System.err.println("Couldn't get I/O for the connection to " +
        hostName);
        System.exit(1);
    }
}

02-09 17:48:09.920 13635-13635/? E/dalvikvm: Could not find class 'android.graphics.drawable.RippleDrawable', referenced from method android.support.v7.widget.AppCompatImageHelper.hasOverlappingRendering
02-09 17:48:09.970 13635-13635/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.geodesick.testapp, PID: 13635
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.geodesick.testapp/com.geodesick.testapp.MainActivity}: android.os.NetworkOnMainThreadException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2413)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2471)
        at android.app.ActivityThread.access$900(ActivityThread.java:175)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:146)
        at android.app.ActivityThread.main(ActivityThread.java:5603)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: android.os.NetworkOnMainThreadException
        at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1166)
        at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
        at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
        at java.net.InetAddress.getAllByName(InetAddress.java:214)
        at java.net.Socket.tryAllAddresses(Socket.java:109)
        at java.net.Socket.<init>(Socket.java:178)
        at java.net.Socket.<init>(Socket.java:150)
        at com.geodesick.testapp.MainActivity.onCreate(MainActivity.java:28)
        at android.app.Activity.performCreate(Activity.java:5458)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2377)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2471) 
        at android.app.ActivityThread.access$900(ActivityThread.java:175) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:146) 
        at android.app.ActivityThread.main(ActivityThread.java:5603) 
        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:1283) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099) 
        at dalvik.system.NativeStart.main(Native Method)

https://stackoverflow.com/questions/23353173/unfortunately-myapp-has-stopped-how-can-i-solve-this https://stackoverflow.com/questions/6343166/how-do-i-fix-android-os-networkonmainthreadexception — CommonsWare, Feb 09 '19 at 17:48
@CommonsWare: I guess the answer below "borrowed" one of your links :/ — Hovercraft Full Of Eels, Feb 09 '19 at 18:19

Erik · Answer 1 · 2019-02-09T20:40:33.167

You cant run network operations on the main Android UI thread.

here´s a solution spinning up an Asynctask that run on it´s own thread:

class DoSocketOperation extends AsyncTask<String, Void, YourResult result> {
    protected YourResult doInBackground(String... urls) {
        // custom class to transport network result(you create it)
        YourResult result = nesw YourResult();
        //Host IP.
        String hostName = "192.168.0.3";
        //Port Number.
        int portNumber = 6666;
        try {
                //Create a connection with IP on selected port.
                Socket echoSocket = new Socket(hostName, portNumber);
                //Create an outputStream with the connection.
                PrintWriter out = new PrintWriter(echoSocket.getOutputStream(), true);

                //Send data out the outputStream to server.
                out.println("Hello");
                result.setSucessOrSometing(true); (you create this)
                //Catch Exceptions
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host " + hostName);
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to " +
                    hostName);
            System.exit(1);
        }
        return YourResult;
    }

    protected void onPostExecute(YourResult result) {

        if(result != null){
            // Now your on the main ui thread again, do something on the main ui thread with the result
        }
    }
}

Holy Crap! i guess i should have just started it in android! ive been jumping through loops for days. java is hard! — Geo, Feb 09 '19 at 18:04
@erik: if the question is answered by simply posting a link to another duplicate question, then *don't answer it* but rather vote to close as a duplicate. — Hovercraft Full Of Eels, Feb 09 '19 at 18:06
Thanks Erik ."You cant run network operations on the main Android UI thread" — Geo, Feb 09 '19 at 18:08
Please see [this relevant meta post](https://meta.stackoverflow.com/questions/311044/are-internal-link-only-answers-advisable) — Hovercraft Full Of Eels, Feb 09 '19 at 18:15
Plagiarizing the code from the answer to the duplicate question doesn't really help change the status of this answer. Please consider deleting — Hovercraft Full Of Eels, Feb 09 '19 at 20:08

Java code wont work in android studio. Port communication

1 Answers1