Android: Can't get http data with AsyncTask

Question

I'm creating a news app. Usaly when I getting HTTP data it works fine, but now in my app I'm using RecyclerView+CardView and I've (I supose some kind of logical error because of it). I've tried to use different libraries like OkHttp and Retrofit but the doesn't work as well. I completley sure that I've got a core misunderstanding.

public class MainActivity extends AppCompatActivity {
private List<Message> list;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    list = new ArrayList<>();
    DownloadTask task = new DownloadTask();
    String result = null;
    try {

        result = task.execute("https://newsapi.org/v2/top-headlines?country=us&apiKey=(MyApi)").get();

    } catch (InterruptedException e) {

        e.printStackTrace();

    } catch (ExecutionException e) {

        e.printStackTrace();
    }
    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
    RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setHasFixedSize(true);
    AtomicReference<MyCustomAdapter> adapter = null;
    adapter.set(new MyCustomAdapter(initData(result)));
    Log.i("result","Heh "+result);
    recyclerView.setAdapter(adapter.get());
}

private List<Message> initData(String myDataString) {
    representData(myDataString);
    return list;
}
private void representData(String myJSONDataString){
    JsonParser parser = new JsonParser();
    JsonObject rootObj = parser.parse(myJSONDataString).getAsJsonObject();
    JsonArray articlesArray = rootObj.getAsJsonArray("articles");
    for (JsonElement aa : articlesArray) {
        JsonObject articleObj = aa.getAsJsonObject();
        String title = articleObj.get("title").getAsString();
        String description = articleObj.get("description").getAsString();
        list.add(new Message(title,description));
    }
}
public class DownloadTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... urls) {

        String result = "";
        URL url;
        HttpURLConnection urlConnection = null;

        try {

            url = new URL(urls[0]);

            urlConnection = (HttpURLConnection)url.openConnection();

            InputStream in = urlConnection.getInputStream();

            InputStreamReader reader = new InputStreamReader(in);

            int data = reader.read();

            while (data != -1) {

                char current = (char) data;

                result += current;

                data = reader.read();

            }

            return result;

        }
        catch(Exception e) {

            e.printStackTrace();

            return "Failed";

        }


    }

}

} LogCat

05-21 07:19:48.414 12126-12126/com.example.gmachine.mynewsapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.gmachine.mynewsapp, PID: 12126
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.gmachine.mynewsapp/com.example.gmachine.mynewsapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.util.concurrent.atomic.AtomicReference.set(java.lang.Object)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2804)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2875)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1578)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:156)
    at android.app.ActivityThread.main(ActivityThread.java:6623)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.util.concurrent.atomic.AtomicReference.set(java.lang.Object)' on a null object reference
    at com.example.gmachine.mynewsapp.MainActivity.onCreate(MainActivity.java:61)
    at android.app.Activity.performCreate(Activity.java:6910)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2757)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2875) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1578) 
    at android.os.Handler.dispatchMessage(Handler.java:105) 
    at android.os.Looper.loop(Looper.java:156) 
    at android.app.ActivityThread.main(ActivityThread.java:6623) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832) 
05-21 07:19:48.461 12126-12126/? I/Process: Sending signal. PID: 12126 SIG: 9

Answer 1

change

AtomicReference<MyCustomAdapter> adapter = null;

to

AtomicReference<MyCustomAdapter> adapter = new AtomicReference<>();

Also, please read your error log carefully next time. It clearly states that you have a NullPointerException

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.util.concurrent.atomic.AtomicReference.set(java.lang.Object)' on a null object reference