ListView.setAdapter Null Pointer exception While adapter.getCount show all records and Listview is also not Null

Question

I have an app which populates ListView with a custom adapter and an overflow menu item in the list. From the MainActivity, the custom adapter is called and it calls a class OnAlbumOverflowSelectedListener which implements onClickListner. In its click function, I want to fade all list Items except the clicked one.

When I try to call myListview.seteAdapter(Cus_aptr) it throws null pointer exception. So MainActivity->CustomAdapter-> OnAlbumOverflowSelectedListener->onCLick below is code snippet:

1. main activity
package com.example.shahnaii;

import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;

import java.util.ArrayList;

public class ScrollingActivity extends AppCompatActivity {
    ArrayList<DataModel> dataModels;
    ListView listView;
    private static CustomAdapter adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scrolling);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Open new window to add entries", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        listView = findViewById(R.id.list_myContent);
        dataModels= new ArrayList<>();

        dataModels.add(new DataModel("Apple Pie", "Android 1.0", "1","September 23, 2008"));
        dataModels.add(new DataModel("Banana Bread", "Android 1.1", "2","February 9, 2009"));
        dataModels.add(new DataModel("Cupcake", "Android 1.5", "3","April 27, 2009"));
        dataModels.add(new DataModel("Donut","Android 1.6","4","September 15, 2009"));
        dataModels.add(new DataModel("Eclair", "Android 2.0", "5","October 26, 2009"));
        dataModels.add(new DataModel("Froyo", "Android 2.2", "8","May 20, 2010"));
        dataModels.add(new DataModel("Gingerbread", "Android 2.3", "9","December 6, 2010"));
        dataModels.add(new DataModel("Honeycomb","Android 3.0","11","February 22, 2011"));
        dataModels.add(new DataModel("Ice Cream Sandwich", "Android 4.0", "14","October 18, 2011"));
        dataModels.add(new DataModel("Jelly Bean", "Android 4.2", "16","July 9, 2012"));
        dataModels.add(new DataModel("Kitkat", "Android 4.4", "19","October 31, 2013"));
        dataModels.add(new DataModel("Lollipop","Android 5.0","21","November 12, 2014"));
        dataModels.add(new DataModel("Marshmallow", "Android 6.0", "23","October 5, 2015"));

        //adapter= new CustomAdapter(dataModels,getApplicationContext());
        adapter= new CustomAdapter(dataModels,this);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                DataModel dataModel= dataModels.get(position);

                Snackbar.make(view, dataModel.getName()+"\n"+dataModel.getType()+" API: "+dataModel.getVersion_number(), Snackbar.LENGTH_LONG)
                        .setAction("No action", null).show();
            }
        });


    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_scrolling, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
          switch (id)
        {
            case R.id.action_Menu1: {
                Toast.makeText(getApplicationContext(),"Menu 1 Selected",Toast.LENGTH_SHORT).show();
            }


        }

        return super.onOptionsItemSelected(item);
    }
}

2. custom Adapter
package com.example.shahnaii;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.AlphaAnimation;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.PopupMenu;
import android.widget.TextView;

import com.google.android.material.snackbar.Snackbar;

import java.lang.reflect.Field;
import java.util.ArrayList;



public class CustomAdapter extends ArrayAdapter<DataModel> implements View.OnClickListener{


    Context mContext;
    ArrayList<DataModel> mData;

// View lookup cache
private static class ViewHolder {
    TextView txtName;
    TextView txtType;
    TextView txtVersion;
    ImageView info;
    ImageView overFlow;
    }

    public CustomAdapter(ArrayList<DataModel> data, Context context) {
        super(context, R.layout.row_item, data);
        this.mContext=context;
        this.mData=data;
         }

    @Override
    public void onClick(View v) {

        int position=(Integer) v.getTag();
        Object object= getItem(position);
        DataModel dataModel=(DataModel)object;

        switch (v.getId())
        {
            case R.id.item_info:
                Snackbar.make(v, "Release date " +dataModel.getFeature(), Snackbar.LENGTH_LONG)
                        .setAction("No action", null).show();
                break;

        }


    }

    private int lastPosition = -1;

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // Get the data item for this position
        DataModel dataModel = getItem(position);
        // Check if an existing view is being reused, otherwise inflate the view
        ViewHolder viewHolder; // view lookup cache stored in tag

        final View result;

        if (convertView == null) {

            viewHolder = new ViewHolder();
            LayoutInflater inflater = LayoutInflater.from(getContext());
            convertView = inflater.inflate(R.layout.row_item, parent, false);
            viewHolder.txtName = (TextView) convertView.findViewById(R.id.name);
            viewHolder.txtType = (TextView) convertView.findViewById(R.id.type);
            viewHolder.txtVersion = (TextView) convertView.findViewById(R.id.version_number);
            viewHolder.info = (ImageView) convertView.findViewById(R.id.item_info);
            viewHolder.overFlow = (ImageView) convertView.findViewById(R.id.album_overflow);
            //viewHolder.overFlow.setOnClickListener(new OnAlbumOverflowSelectedListener(mContext,position));
                    result=convertView;

            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
            result=convertView;
        }

        viewHolder.txtName.setText(dataModel.getName());
        viewHolder.txtType.setText(dataModel.getType());
        viewHolder.txtVersion.setText(dataModel.getVersion_number());
        viewHolder.info.setOnClickListener(this);
        viewHolder.info.setTag(position);
        viewHolder.overFlow.setOnClickListener(new OnAlbumOverflowSelectedListener(mContext,mData,position));
        //viewHolder.overFlow.setTag(position);
        // Return the completed view to render on screen
        return result;
    }
}

3. OnAlbumOverflowSelectedListner

package com.example.shahnaii;

import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.view.View;
import android.view.animation.AlphaAnimation;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.PopupMenu;

import com.google.android.material.snackbar.Snackbar;

import java.lang.reflect.Field;
import java.util.ArrayList;

public class OnAlbumOverflowSelectedListener  implements View.OnClickListener  {
    private ListView mListView;
    private ArrayAdapter mArrAdapter;
    private ArrayList uData;
    private final AlphaAnimation mFadeOut = new AlphaAnimation(1.0f, 0.3f);
    private final AlphaAnimation mFadeIn = new AlphaAnimation(0.3f, 1.0f);
    //private MediaStore.Audio.Albums mAlbum;
    private Context mContext;
    private int mPosition;
    private int mAlbum;
     public OnAlbumOverflowSelectedListener(Context con,ArrayList<?>data,int pos)
     {
         mContext=con;
         mPosition = pos;
         this.uData = data;
     }

    @Override
    public void onClick(View v) {
        // This is an android.support.v7.widget.PopupMenu;

        PopupMenu popupMenu = new PopupMenu(mContext, v) {
        };

        popupMenu.inflate(R.menu.menu);
        // Force icons to show
        Object menuHelper;
        Class[] argTypes;
        try {
            Field fMenuHelper = PopupMenu.class.getDeclaredField("mPopup");
            fMenuHelper.setAccessible(true);
            menuHelper = fMenuHelper.get(popupMenu);
            argTypes = new Class[] { boolean.class };
            menuHelper.getClass().getDeclaredMethod("setForceShowIcon",
                    argTypes).invoke(menuHelper, true);
        } catch (Exception e) {
            popupMenu.show();
            return;
        }
        // Force icons to show ends here
        popupMenu.show();

        /*fading process begins-*/
        // Dim out all the other list items if they exist
        CustomAdapter cust_adptr = new CustomAdapter(this.uData,this.mContext);
         Object obj = cust_adptr.getItem(mPosition);
        DataModel dm = (DataModel)obj;

        Snackbar.make(v, "Release date "+cust_adptr.getItem(mPosition).getFeature(), Snackbar.LENGTH_LONG)
                .setAction("No action", null).show();

        mListView = v.findViewById(R.id.list_myContent);
        mListView.setAdapter(cust_adptr);

        int firstPos = mListView.getFirstVisiblePosition() - mListView.getHeaderViewsCount();
        final int ourPos = mArrAdapter.getPosition(mPosition) - firstPos;
        int count = mListView.getChildCount();
        for (int i = 0; i <= count; i++) {
            if (i == ourPos) {
                continue;
            }

            final View child = mListView.getChildAt(i);
            if (child != null) {
                child.clearAnimation();
                child.startAnimation(mFadeOut);
            }
        }

        // Make sure to bring them back to normal after the menu is gone
        popupMenu.setOnDismissListener(new PopupMenu.OnDismissListener() {
            @Override
            public void onDismiss(PopupMenu popupMenu) {
                int count = mListView.getChildCount();
                for (int i = 0; i <= count; i++) {
                    if (i == ourPos) {
                        continue;
                    }

                    final View v = mListView.getChildAt(i);
                    if (v != null) {
                        v.clearAnimation();
                        v.startAnimation(mFadeIn);
                    }
                }
            }
        });
        /*fading process ends*/

    }
}


OnAlbumOverflowSelectedListener class
onlcick method()
{
....

CustomAdapter cust_adptr = new CustomAdapter(this.uData,this.mContext);
         Object obj = cust_adptr.getItem(mPosition);
        DataModel dm = (DataModel)obj;

        Snackbar.make(v, "Release date "+cust_adptr.getItem(mPosition).getFeature(), Snackbar.LENGTH_LONG)
                .setAction("No action", null).show();

        mListView = v.findViewById(R.id.list_myContent);
        mListView.setAdapter(cust_adptr); this code throw null pointer

Please, add error stack and format your code, especially at the end if you need help. https://stackoverflow.com/help/how-to-ask — ardiien, Sep 27 '19 at 08:12

score 1 · Answer 1 · answered Sep 27 '19 at 07:18

1

Check activity_scrolling.xml maybe it do not contain ListView with id R.id.list_myContent.
Can you post the error log also?

answered Sep 27 '19 at 07:18

Subham Naik

411
5
12

No R.id.list_myContent is in other xml file and below is error code 2019-09-27 15:35:17.090 11129-11129/com.example.shahnaii E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.shahnaii, PID: 11129 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at com.example.shahnaii.OnAlbumOverflowSelectedListener.onClick(OnAlbumOverflowSelectedListener.java:69) at android.view.View.performClick(View.java:6310) at and – Naseem Khan Sep 27 '19 at 10:10

score 0 · Answer 2 · edited Sep 27 '19 at 10:13

0

Try to find the id. In Major cases if you miss declaring id and implementing any operation on that view or button you will get NullPointerException
Sometimes if you are setting any value which is coming null from back end to Text view or Button Image view, then also you will get NullPointerException.
Or you can put your code in try-catch to avoid the Crash

edited Sep 27 '19 at 10:13

Alexey Usharovski

1,404
13
31

answered Sep 27 '19 at 09:19

Arvind Patil

1
3

ListView.setAdapter Null Pointer exception While adapter.getCount show all records and Listview is also not Null

2 Answers2