Question

right now I’m trying to open database, using

db=SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READONLY);
        Cursor resultset = db.query("person_table", null, null, null, null, null, null);

so I’m using Cursor to get each of the result set return by the db query. Each of the result set return I add to the array to be view in the ListView. Below is my code for fetch data from db

package com.android.my.mypackage;

import android.app.ListActivity;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.Cursor;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.List;

public class personDetail extends ListActivity{

    private static String DBPATH="data/data/com.android.my.mypackage/databases/";
    private static String DBNAME="persondb.db";
    private View refView;
    public ListView personlist;

    public personDetail(View v, ListView l){
        refView = v;
        personlist = l;
    }

    public void DisplayPersonDetail(){
        SQLiteDatabase db=null;
        String path=DBPATH+DBNAME;

        db=SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READONLY);
        Cursor resultset = db.query("person_table", null, null, null, null, null, null);
        if(resultset.getCount()==0){            
            /*please ignore this block*/
        }else{
            resultset.moveToFirst();
            List<String> arl = new ArrayList<String>();         
            while(resultset.isAfterLast()==false){

                arl.add(resultset.getString(6).toString() + "@@" + resultset.getString(1).toString());                              
                resultset.moveToNext();                         
            }
            //Toast.makeText(refView.getContext(), "Arl value " + arl, Toast.LENGTH_LONG).show();
            personlist.setAdapter(new PersonAdapter(this, arl));
        }       
    }

}

And below is PersonAdapter class

package com.android.my.mypackage;

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

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.widget.ImageView;


public class PersonAdapter extends ArrayAdapter<String>{
    private static Activity context;
    private final List<String> list;

    public PersonAdapter(Activity c, List<String> list){
        super(context, R.layout.person_adapter, list);
        this.context = c;
        this.list = list;
    }

    static class ViewHolder{
        private TextView descHolder;
        private ImageView typeHolder;
    }

    public View getView(int position, View convertview, ViewGroup group){

        ViewHolder holder;
        View lView = convertview;

        if(lView==null){
            LayoutInflater inf = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            lView = inf.inflate(R.layout.person_adapter, group, true);
            holder = new ViewHolder();
            holder.descHolder = (TextView) lView.findViewById(R.id.personDescLbl);
            holder.typeHolder = (ImageView) lView.findViewById(R.id.personCategoryImage);
        }else{
            holder = (ViewHolder) lView.getTag();
        }

        holder.descHolder.setText(list.get(position).toString().split("@@")[0]);
        String category = list.get(position).toString().split("@@")[1];
        if(category.equals("Male")){
            holder.typeHolder.setImageResource(R.drawable.male);
        }else{
            holder.typeHolder.setImageResource(R.drawable.female);
        }               
        return lView;
    }
}

and my person_adapter layout to inflate with list view

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
    <TextView 
        android:id="@+id/personDescLbl"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:gravity="center_vertical"/>
    <ImageView 
        android:id="@+id/personCategoryImage"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"/>       
</LinearLayout>

My code is based on tutorial from this site. But i get Nullpointer exception error in PersonAdapter class which is pointed to

super(context, R.layout.person_adapter, list);

Before this I display the result set using table layout and it”s working find. But it is not a good practicall using table layout to display large amount of data it as it counsume time and memory. So please help me accomplished the listView adapter. Thanks.

Answer 1

In your PersonAdapter, your context field is null when you call the super constructor.
You only initialize it on the second line. Your should pass the activity as the first parameter of super (you called it c), and then affect your context field.

public class PersonAdapter extends ArrayAdapter<String>{
    private static Activity context;
    ...

    public PersonAdapter(Activity c, List<String> list){
        super(c, R.layout.person_adapter, list);
        this.context = c;
        this.list = list;
   }