No solution works for handling of NetworkOnMainThreadException

Issue

After many hours with searching for handling of NetworkOnMainThreadException, I have used code from this video in YouTube

Very well explained but it doesn't in my project... Then I have tried to use the solution from Stack Overflow (e.g. runOnUiThread, AsyncTask, Handler) from following link:

https://stackoverflow.com/questions/3875184/cant-create-handler-inside-thread-that-has-not-called-looper-prepare

Currently I'm trying with AsyncTask again but the result is always the same- Exception: java.lang.RuntimeException:

Can't create handler inside thread Thread[AsyncTask #1,5,main] that has not called Looper.prepare()

The idea was to get datas from the class actualLottoNumbers over the method sendGet. It works with Eclipse but not with Android- I know now why but it works anyway not.

This is not a duplicate, because I have read the other questions since 3 days 10 times and tried every solution, but I think I have not really understood it.

Here is the code with AsyncTask which doesn't work:

//it doesn't matter the class Retrievdata is after or before onCreate method- it's always Exception
class Retrievedata extends AsyncTask<Void, Void, Void> {
    String var112="null";
    @Override
    protected Void doInBackground(Void... voids) {

        try {

            actualLottoNumbers var1 = new actualLottoNumbers();
            var112 = var1.sendGet("ff");
            while ((var1.sendGet("ff") != null)) {
                var112=var1.sendGet("ff");
            }



        } catch (MalformedURLException e) {
            e.printStackTrace();
            //var112= e.toString();
        } catch (Exception e) {
            e.printStackTrace();
            //var112= e.toString();
        }
        return null;
    }
    @Override
    protected void onPostExecute(Void result) {

        setContentView(R.layout.activity_zufallsgenerator);
        TextView text_view_id1 = (TextView) findViewById(R.id.text_view_id1);
        text_view_id1.setText(var112);

        //TextView text_prompt = (TextView) findViewById(R.id.text_prompt);
        //text_prompt.setText("Finished!");

        super.onPostExecute(result);
    }
};


@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_zufallsgenerator);

    text_prompt = (TextView) findViewById(R.id.text_prompt);
    text_view_id1 = (TextView) findViewById(R.id.text_view_id1);
    bindViews();

    text_prompt.setText("wait...");

//Button for activity- generate numbers 

    mGenerateButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            generateRandomNumbers();
        }
    });
   new Retrievedata().execute();
    text_prompt = (TextView) findViewById(R.id.text_prompt);
    text_view_id1 = (TextView) findViewById(R.id.text_view_id1);
    bindViews();

};
   new Retrievedata().execute();
    text_prompt = (TextView) findViewById(R.id.text_prompt);
    text_view_id1 = (TextView) findViewById(R.id.text_view_id1);
    bindViews();

};
   new Retrievedata().execute();
    text_prompt = (TextView) findViewById(R.id.text_prompt);
    text_view_id1 = (TextView) findViewById(R.id.text_view_id1);
    bindViews();

};

Full logcat:

2019-08-12 14:10:55.893 25359-25456/com. W/System.err: java.lang.RuntimeException: Can't create handler inside thread Thread[AsyncTask #1,5,main] that has not called Looper.prepare()
    2019-08-12 14:10:55.893 25359-25456/com. W/System.err:     at android.os.Handler.<init>(Handler.java:205)
    2019-08-12 14:10:55.893 25359-25456/com. W/System.err:     at android.os.Handler.<init>(Handler.java:118)
    2019-08-12 14:10:55.894 25359-25456/com. W/System.err:     at android.app.Activity.<init>(Activity.java:831)
    2019-08-12 14:10:55.894 25359-25456/com. W/System.err:     at android.support.v4.app.SupportActivity.<init>(ComponentActivity.java:46)
    2019-08-12 14:10:55.894 25359-25456/com. W/System.err:     at android.support.v4.app.FragmentActivity.<init>(FragmentActivity.java:68)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at android.support.v7.app.AppCompatActivity.<init>(AppCompatActivity.java:62)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at com.generator23.actualLottoNumbers.<init>(actualLottoNumbers.java:15)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at com.generator23.Zufallsgenerator$Retrievedata.doInBackground(Zufallsgenerator.java:112)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at com.generator23.Zufallsgenerator$Retrievedata.doInBackground(Zufallsgenerator.java:105)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:333)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
    2019-08-12 14:10:55.898 25359-25456/com. W/System.err:     at java.lang.Thread.run(Thread.java:764)

And here is the class from which I get the data for sendGet method in the activity with layout:

public class actualLottoNumbers extends AppCompatActivity {


    private final String USER_AGENT = ("Mozilla/5.0 (Linux; Android 4.4; Nexus 4 Build/KRT16H) AppleWebKit/537.36(KHTML, like Gecko) Version/4.0 Chrome/30");
    private TextView textView1;


    // HTTP GET request
    public String sendGet(String var11) throws Exception {

        String url = "https://www....";

        URL obj = new URL(url);
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();

        // optional default is GET
        con.setRequestMethod("GET");

        //add request header
        con.setRequestProperty("User-Agent", USER_AGENT);

        int responseCode = con.getResponseCode();


        BufferedReader in = new BufferedReader(
                new InputStreamReader(con.getInputStream()));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();


        //get the text from span class of the lotto
        String html=response.toString();
        Document doc = Jsoup.parse(html);
        Elements elements = doc.select("span.LottoBall__circle");
        for (Element e : elements) {
    //        System.out.println("Allt text:" + e.text());
     //       System.out.println("Only messageBody text:" + e.ownText()); var11=e.text();
        } return var11;

    } }

Solution

First of all you must not use AsyncTask in Activity, because you can create a memory leak. You should use AsyncTaskLoader in the Activity. But more elegant way is to use rxjava2 and retrofit2 for you needs.

The working code with AsyncTask bellow:

public class MainActivity extends AppCompatActivity {
    private RetrieveData retrieveData;
    private TextView text_prompt;
    private TextView text_view_id1;
    private Button mGenerateButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        text_prompt = (TextView) findViewById(R.id.text_prompt);
        text_view_id1 = (TextView) findViewById(R.id.text_view_id1);
        mGenerateButton = findViewById(R.id.mGenerateButton);

        mGenerateButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                retrieveData = new RetrieveData();
                retrieveData.execute();
            }
        });
    }

    class RetrieveData extends AsyncTask<Void, Void, String> {
        String var112 = "null";

        @Override
        protected String doInBackground(Void... voids) {

            try {
                ActualLottoNumbers var1 = new ActualLottoNumbers();
                var112 = var1.sendGet("ff");
                while ((var1.sendGet("ff") != null)) {
                    var112 = var1.sendGet("ff");
                }
            } catch (Exception e) {
                e.printStackTrace();
                //var112= e.toString();
            }
            return var112;
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            text_view_id1.setText(result);
        }
    }

    private class ActualLottoNumbers {
        private final String USER_AGENT = ("Mozilla/5.0 (Linux; Android 4.4; Nexus 4 Build/KRT16H) AppleWebKit/537.36(KHTML, like Gecko) Version/4.0 Chrome/30");
        private TextView textView1;

        // HTTP GET request
        public String sendGet(String var11) throws Exception {

            String url = "https://www....";

            URL obj = new URL(url);
            HttpURLConnection con = (HttpURLConnection) obj.openConnection();

            // optional default is GET
            con.setRequestMethod("GET");

            //add request header
            con.setRequestProperty("User-Agent", USER_AGENT);

            int responseCode = con.getResponseCode();

            BufferedReader in = new BufferedReader(
                    new InputStreamReader(con.getInputStream()));
            String inputLine;
            StringBuffer response = new StringBuffer();

            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();

            //get the text from span class of the lotto
            String html = response.toString();

            return var11;
        }
    }
}

Answered By - Matthew Strukov