Onitemclicklistener with Customadapter, java.lang.Nullpointerexception error:

Question

Good Afternoon, I’m using a listview to display some images per url and cache them. So far, so good. But when I put Onitemclicklistener just to show Titulo with a message it gives the error

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object erikjota9.testeurl.AdapterListView.getItem(int)' on a null object reference

Mainactivity

package erikjota9.testeurl;

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

import com.nostra13.universalimageloader.core.DisplayImageOptions;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;
import com.nostra13.universalimageloader.core.display.FadeInBitmapDisplayer;
import com.nostra13.universalimageloader.core.listener.PauseOnScrollListener;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private ListView lvPosts;
    private List<Post> list;
    private ImageLoader mImageLoader;
    public AdapterListView Adaptador;
    public Post postteste;

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

        list = new ArrayList<Post>();
        list.add(new Post("Title 1", "https://cdn.ndtv.com/tech/images/gadgets/pikachu_hi_pokemon.jpg?output-quality=70&output-format=webp"));
        list.add(new Post("Title 2", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 3", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 4", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 5", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 6", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 7", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 8", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 9", "https://image.ibb.co/nvOv9d/24bbe5962453d06619a0f29aae3a3d5e.jpg"));
        list.add(new Post("Title 10", ""));
        list.add(new Post("Title 11", "http://www.villopim.com.br/android/universal-image-loader/teste.png"));


        DisplayImageOptions mDisplayImageOptions = new DisplayImageOptions.Builder()
                .showImageForEmptyUri(R.drawable.ic_launcher_background)
                .showImageOnFail(R.drawable.ic_launcher_background)
                .showImageOnLoading(R.drawable.ic_launcher_background)
                .cacheInMemory(true)
                .cacheOnDisk(true)
                //.displayer(new FadeInBitmapDisplayer(1000))
                .build();

        ImageLoaderConfiguration conf = new ImageLoaderConfiguration.Builder(MainActivity.this)
                .defaultDisplayImageOptions(mDisplayImageOptions)
                .memoryCacheSize(50 * 1024 * 1024)
                .diskCacheSize(50 * 1024 * 1024)
                .threadPoolSize(5)
                .writeDebugLogs()
                .build();
        mImageLoader = ImageLoader.getInstance();
        mImageLoader.init(conf);

        PauseOnScrollListener mPauseOnScrollListener = new PauseOnScrollListener(mImageLoader, true, true);

        lvPosts = (ListView) findViewById(R.id.lvPosts);
        lvPosts.setAdapter(new AdapterListView(MainActivity.this, list, mImageLoader));
        lvPosts.setOnScrollListener(mPauseOnScrollListener);
        lvPosts.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {


                Post pick = (Post) Adaptador.getItem(position);

                String message = "You Selected " + pick.getTitle();               

                Toast.makeText(MainActivity.this, message, Toast.LENGTH_SHORT).show();

            }
        });
    }


    @Override
    public void onDestroy(){
        super.onDestroy();
        mImageLoader.stop();
    }
}

Post.java

package erikjota9.testeurl;

public class Post {
    public String title;
    private String urlImage;



    public Post(String title, String urlImage){
        this.title = title;
        this.urlImage = urlImage;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getUrlImage() {
        return urlImage;
    }
    public void setUrlImage(String urlImage) {
        this.urlImage = urlImage;
    }
}

Adapterlistview

    package erikjota9.testeurl;

import java.util.List;

import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.assist.FailReason;
import com.nostra13.universalimageloader.core.listener.ImageLoadingListener;
import com.nostra13.universalimageloader.core.listener.ImageLoadingProgressListener;

import android.content.Context;
import android.graphics.Bitmap;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class AdapterListView extends BaseAdapter {
    public List<Post> list;
    private LayoutInflater inflater;
    private ImageLoader mImageLoader;


    public AdapterListView(Context context, List<Post> list, ImageLoader mImageLoader){

        this.list = list;
        this.inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        this.mImageLoader = mImageLoader;

    }


    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;

        if(convertView == null){
            convertView = inflater.inflate(R.layout.item, null);
            holder = new ViewHolder();
            convertView.setTag(holder);

            holder.ivPost = (ImageView) convertView.findViewById(R.id.ivPost);
            holder.tvPost = (TextView) convertView.findViewById(R.id.tvPost);
        }
        else{
            holder = (ViewHolder) convertView.getTag();
        }

        holder.tvPost.setText(list.get(position).getTitle());

        // IMAGE LOADER
        mImageLoader.displayImage(list.get(position).getUrlImage(),
            holder.ivPost,
            null,
            new ImageLoadingListener(){

                @Override
                public void onLoadingCancelled(String uri, View view) {
                    Log.i("Script", "onLoadingCancelled()");
                }

                @Override
                public void onLoadingComplete(String uri, View view, Bitmap bmp) {
                    Log.i("Script", "onLoadingComplete()");
                }

                @Override
                public void onLoadingFailed(String uri, View view, FailReason fail) {
                    Log.i("Script", "onLoadingFailed("+fail+")");
                }

                @Override
                public void onLoadingStarted(String uri, View view) {
                    Log.i("Script", "onLoadingStarted()");
                }

            }, new ImageLoadingProgressListener(){
                @Override
                public void onProgressUpdate(String uri, View view, int current, int total) {
                    Log.i("Script", "onProgressUpdate("+uri+" : "+total+" : "+current+")");
                }
            });

        return convertView;
    }


    private class ViewHolder{
        public ImageView ivPost;
        public TextView tvPost;
    }
}

Answer 1

You did not initialize the Adapter object, you are creating an Adapter instance directly in the setAdapter method.

To solve you can replace

lvPosts.setAdapter(new AdapterListView(MainActivity.this, list, mImageLoader));

for

 Adaptador = new AdapterListView(MainActivity.this, list, mImageLoader);
 lvPosts.setAdapter(Adaptador);