Attempt to invoke virtual method [Null object reference]

Question

I'm spending the last 5 days trying solve this problem. I really do not have any idea about how to solve it. I'm getting Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference. Check my code:

RecyclerView.java

package etes.xdda.music;
import android.app.Dialog;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.media.MediaPlayer;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.List;


public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> implements View.OnClickListener{

    Context mContext;
    List<mList> mData;
    Dialog myDialog;

    private MediaPlayer mediaPlayer;
    private int playbackPosition=0;

    private LinearLayout menu_dialog;
    public RecyclerViewAdapter(Context mContext, List<mList> mData) {
        this.mContext = mContext;
        this.mData = mData;
    }

    public void onClick(View view) {
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v;
        v = LayoutInflater.from(mContext).inflate(R.layout.item_list, parent, false);
        final MyViewHolder vHolder = new MyViewHolder(v);

        // Dialog ini
        myDialog = new Dialog(mContext);
        myDialog.setContentView(R.layout.dialog);
        myDialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

        vHolder.item_play.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {

                TextView dialog_name_tv = (TextView) myDialog.findViewById(R.id.dialog_name_id);
                TextView dialog_phone_tv = (TextView) myDialog.findViewById(R.id.dialog_author_id);
                ImageView dialog_contact_img = (ImageView) myDialog.findViewById(R.id.dialog_img);
                dialog_name_tv.setText(mData.get(vHolder.getAdapterPosition()).getName());
                dialog_phone_tv.setText(mData.get(vHolder.getAdapterPosition()).getPhone());
                dialog_contact_img.setImageResource(mData.get(vHolder.getAdapterPosition()).getPhoto());
                //Toast.makeText(mContext, "Test click "+String.valueOf(vHolder.getAdapterPosition()), Toast.LENGTH_SHORT).show();
                myDialog.show();
            }
        });
        vHolder.menu_play.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                menu_dialog = v.getRootView().findViewById(R.id.menu_dialog);
                menu_dialog.setVisibility(v.VISIBLE);

                MainActivity a = new MainActivity();
                a.initAudio(v.getContext(), mData.get(vHolder.getAdapterPosition()).getURL());
                MainActivity.setMargins(v.getRootView().findViewById(R.id.viewpager_id), 0,0,0,100);
            }
        });
        return vHolder;
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {

        holder.tv_name.setText(mData.get(position).getName());
        holder.tv_author.setText(mData.get(position).getPhone());
        holder.img.setImageResource(mData.get(position).getPhoto());
    }

    @Override
    public int getItemCount() {
        return mData.size();
    }

    public static class MyViewHolder extends RecyclerView.ViewHolder {

        private ImageButton item_play;
        private LinearLayout menu_play;
        private TextView tv_name;
        private TextView tv_author;
        private TextView tv_url;
        private ImageView img;

        public MyViewHolder(View itemView) {
            super(itemView);
            item_play = itemView.findViewById(R.id.info_id);
            menu_play = itemView.findViewById(R.id.list_item_id);

            tv_name = (TextView) itemView.findViewById(R.id.name_list);
            tv_author = (TextView) itemView.findViewById(R.id.author_list);
            img = (ImageView) itemView.findViewById(R.id.img_contact);
        }
    }
}

Note that I'm invoking MainActivity.java in this part:

vHolder.menu_play.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v)
        {
            menu_dialog = v.getRootView().findViewById(R.id.menu_dialog);
            menu_dialog.setVisibility(v.VISIBLE);

            MainActivity a = new MainActivity();
            a.initAudio(v.getContext(), mData.get(vHolder.getAdapterPosition()).getURL());
            MainActivity.setMargins(v.getRootView().findViewById(R.id.viewpager_id), 0,0,0,100);
        }
    });

And here's my MainActivity.java

package etes.xdda.music;

import android.annotation.SuppressLint;
import android.content.Context;
import android.media.MediaPlayer;
import android.net.Uri;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;


public class MainActivity extends AppCompatActivity {

    private DrawerLayout nDrawerLayout;
    private ActionBarDrawerToggle mToggle;

    private TabLayout tabLayout;
    private ViewPager viewPager;
    private viewPagerAdapter adapter;
    public LinearLayout menu_dialog;
    private String player_status = "playing";
    private ImageButton player_img;



    private static MediaPlayer mediaPlayer;

    @SuppressLint("RestrictedApi")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        nDrawerLayout = findViewById(R.id.drawer);

        menu_dialog = findViewById(R.id.menu_dialog);
        menu_dialog.setVisibility(View.GONE);

        player_img = findViewById(R.id.playorpause);
        player_img.setOnClickListener(new View.OnClickListener() {
                                          @Override
                                          public void onClick(View view) {
                                              //setMargins(viewPager, 0,0,0,110);
                                              if (player_status == "playing") {
                                                  player_img.setImageResource(R.drawable.ic_play_arrow_black_24dp);
                                                  meplayer.pauseAudio();
                                                  player_status = "paused";
                                              } else {
                                                  player_img.setImageResource(R.drawable.ic_pause_black_24dp);
                                                  meplayer.startAudio();
                                                  player_status = "playing";
                                              }
                                          }
                                      });



        //menu_dialog.setLayoutParams(new LinearLayout.LayoutParams(0, 0));

        mToggle = new ActionBarDrawerToggle(this, nDrawerLayout, R.string.open, R.string.close);
        nDrawerLayout.addDrawerListener(mToggle);
        getSupportActionBar().setDefaultDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        tabLayout = findViewById(R.id.tablayout_id);
        viewPager = findViewById(R.id.viewpager_id);
        //viewPager.setLayoutParams(new ViewPager.LayoutParams(0, 0));
        //setMarginBottom(viewPager, 0);
        setMargins(viewPager, 0,0,0,0);

        adapter = new viewPagerAdapter(getSupportFragmentManager());

        //Add fragments here
        adapter.addFragment(new fragmentList(), ""); //Lista de música
        adapter.addFragment(new fragmentFrequent(), ""); //Frequentes
        adapter.addFragment(new fragmentPlayList(), ""); //Playlist

        viewPager.setAdapter(adapter);
        tabLayout.setupWithViewPager(viewPager);

        tabLayout.getTabAt(0).setIcon(R.drawable.ic_music_note_black_24dp); //Lista de música
        tabLayout.getTabAt(1).setIcon(R.drawable.ic_filter_list_black_24dp); // Frequentes
        tabLayout.getTabAt(2).setIcon(R.drawable.ic_queue_music_black_24dp); // Playlist
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (mToggle.onOptionsItemSelected(item)) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mToggle.syncState();
    }
    public static void setMargins (View v, int l, int t, int r, int b) {
        if (v.getLayoutParams() instanceof ViewGroup.MarginLayoutParams) {
            ViewGroup.MarginLayoutParams p = (ViewGroup.MarginLayoutParams) v.getLayoutParams();
            p.setMargins(l, t, r, b);
            v.requestLayout();
        }
    }

    public void initAudio(final Context context, final String url) {
        if (mediaPlayer == null) {
            mediaPlayer = MediaPlayer.create(context, Uri.parse(url));
        }
        mediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mp) {
                //Toast.makeText(context, "TEST", Toast.LENGTH_LONG).show();
                killMediaPlayer();
                updateLayout();

            }
        });
        mediaPlayer.start();
    }

    private static void killMediaPlayer() {
        if (mediaPlayer != null) {
            try {
                mediaPlayer.reset();
                mediaPlayer.release();
                mediaPlayer = null;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    private void updateLayout() {
    try {
        menu_dialog = findViewById(R.id.menu_dialog);
        menu_dialog.setVisibility(View.GONE);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

And the part of code that is giving crash is this:

private void updateLayout() {
    try {
        menu_dialog = findViewById(R.id.menu_dialog);
        menu_dialog.setVisibility(View.GONE);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

@edit: I have added this piece of code, I don't know if can help

fragmentList.java

package etes.xdda.music;

import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.List;

public class fragmentList extends Fragment {

    View v;
    private RecyclerView myrecyclerview;
    private List<mList> lstContact;

    private String URL_JSON = "https://pastebin.com/raw/fG3zd40U";
    private JsonArrayRequest ArrayRequest;
    private RequestQueue requestQueue ;
    MainActivity activity;

    public fragmentList() {
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        v = inflater.inflate(R.layout.list_fragment,container,false);
        myrecyclerview = (RecyclerView) v.findViewById(R.id.list_recyclerview);
        RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(activity, lstContact);
        myrecyclerview.setLayoutManager(new LinearLayoutManager(getActivity()));
        myrecyclerview.setAdapter(recyclerViewAdapter);
        return v;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstaceState) {
        super.onCreate(savedInstaceState);
        _JSONcall();
    }


    public void _JSONcall() {

        lstContact = new ArrayList<>();
        ArrayRequest = new JsonArrayRequest(URL_JSON, new Response.Listener<JSONArray>() {
            @Override
            public void onResponse(JSONArray response) {

                JSONObject jsonObject = null;

                for (int i = 0 ; i<response.length();i++) {
                    try {

                        jsonObject = response.getJSONObject(i);

                        lstContact.add(new mList(jsonObject.getString("name"), jsonObject.getString("description"), jsonObject.getString("link"), R.drawable.ic_play_circle_filled_black_24dp));
                    }
                    catch (JSONException e) {
                        e.printStackTrace();
                        Toast.makeText(getActivity(), "Error 1!",
                                Toast.LENGTH_LONG).show();
                    }
                }

            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(getActivity(), "Error 3!",
                        Toast.LENGTH_LONG).show();
            }
        });


        requestQueue = Volley.newRequestQueue(getActivity().getApplicationContext());
        requestQueue.add(ArrayRequest);
    }
}

Please, help me, I have no more ideas about what I should do. Thank you

try to comment this one `menu_dialog.setVisibility(View.GONE);` . lets see if it is still working or not — Ticherhaz FreePalestine, Sep 23 '18 at 01:30
I want make gone this part: http://prntscr.com/kxkw8i (The linearlayout is inside a relativelayout) — Karlna, Sep 23 '18 at 01:31
http://prntscr.com/kxkwzj .Not working, I believe that `menu_dialog` is not being recognized — Karlna, Sep 23 '18 at 01:34
this one, you already have this one `menu_dialog = findViewById(R.id.menu_dialog); on onCreate(). ` . you need to remove it from the `private void updateLayout() { try { menu_dialog = findViewById(R.id.menu_dialog); //remove this one menu_dialog.setVisibility(View.GONE); } catch (Exception e) { e.printStackTrace(); } }` — Ticherhaz FreePalestine, Sep 23 '18 at 01:59

varunkr · Accepted Answer · 2018-09-23T01:53:04.303

1

Just taking a look at your code, it looks like you are doing many things wrong. Such as this line

        MainActivity a = new MainActivity();

You can't instantiate lifecycle components like Services, Activities, Fragments etc this way. Android provides you these components when you call start methods etc. The activity that is created as a result of the above line doesn't go through the lifecycle calls that an activity that is started via using startActivity. As a result, the setContentView of the activity is never called and you get this error. You have to remove this line and implement this properly and the error will go away.

Also just to add, you are actually creating a new instance of the activity when one is already running when you need to call the methods on the old instance that was started.

Edit: Try like this.

MainActivity activity;
List<mList> mData;
Dialog myDialog;

private MediaPlayer mediaPlayer;
private int playbackPosition=0;

private LinearLayout menu_dialog;
public RecyclerViewAdapter(MainActivity activity, List<mList> mData) {
    this.activity = activity;
    this.mData = mData;
}

And then

vHolder.menu_play.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v)
        {
            menu_dialog = v.getRootView().findViewById(R.id.menu_dialog);
            menu_dialog.setVisibility(v.VISIBLE);

            activity.initAudio(v.getContext(), mData.get(vHolder.getAdapterPosition()).getURL());
            activity.setMargins(v.getRootView().findViewById(R.id.viewpager_id), 0,0,0,100);
        }
    });

Also remove static from the main activity functions

edited Sep 23 '18 at 01:53

answered Sep 23 '18 at 01:35

varunkr

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I'm not able to call `InitAudio`(MainActivity) from **RecyclerView.java** without this line. I'll get `Non-static method cannot be referenced from a static context` – Karlna Sep 23 '18 at 01:38
1

@Karlna Pass your activity object instead of the context object in the recyclerView constructor. Then you can call these methods on those objects. – varunkr Sep 23 '18 at 01:39
Can you give me an example, or a link to read about? Sorry, I'm just trying to learn – Karlna Sep 23 '18 at 01:43
@Karlna Edited the ans – varunkr Sep 23 '18 at 01:53
The app crash when start. I'm getting now `Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference`. The line is `v = LayoutInflater.from(activity).inflate(R.layout.item_list, parent, false);` – Karlna Sep 23 '18 at 02:08
@Karlna Instead of doing RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(activity, lstContact); Use RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(this, lstContact); ALso remove MainActivity param that you added. No need for that – varunkr Sep 23 '18 at 02:14
1

I'm not able to put `this`. I get this error: `incompatible types: fragmentList cannot be converted to Context` :( – Karlna Sep 23 '18 at 02:21
I see, it is a Fragment, not an activity. Use getActivity() instead of `this` – varunkr Sep 23 '18 at 02:23
`error: incompatible types: FragmentActivity cannot be converted to MainActivity` – Karlna Sep 23 '18 at 02:25
have you used a FragmentActivity somewhere? I can't see. Does `(MainActivity)getActivity()` instead of `getActivity()` work? – varunkr Sep 23 '18 at 02:40
I love you. It works!!!! Thank you very much, my hero. – Karlna Sep 23 '18 at 02:50
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/180602/discussion-between-varunkr-and-karlna). – varunkr Sep 23 '18 at 02:51

Attempt to invoke virtual method [Null object reference]

1 Answers1