Problem of cursor positioning

Question

Logcat is accusing a problem of NullPointerException, but I can’t identify it. From my point of view, it’s right. I know there’s a problem in lines 34 and 39 of ContactRegister that lead to condition if(moveToFirst()) in the ContactRepository, but I can’t understand which error. It might be a cursor positioning problem?

 E/AndroidRuntime(914): FATAL EXCEPTION: main
 E/AndroidRuntime(914): Process: br.com.contactsmanager, PID: 914
 E/AndroidRuntime(914): java.lang.RuntimeException: Unable to start activity ComponentInfo{br.com.contactsmanager/br.com.contactsmanager.ContactRegister}: java.lang.NullPointerException
 E/AndroidRuntime(914): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
 E/AndroidRuntime(914): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
 E/AndroidRuntime(914): at android.app.ActivityThread.access$700(ActivityThread.java:135)
 E/AndroidRuntime(914): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
 E/AndroidRuntime(914): at android.os.Handler.dispatchMessage(Handler.java:102)
 E/AndroidRuntime(914): at android.os.Looper.loop(Looper.java:137)
 E/AndroidRuntime(914): at android.app.ActivityThread.main(ActivityThread.java:4998)
 E/AndroidRuntime(914): at java.lang.reflect.Method.invokeNative(Native Method)
 E/AndroidRuntime(914): at java.lang.reflect.Method.invoke(Method.java:515)
 E/AndroidRuntime(914): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
 E/AndroidRuntime(914): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
 E/AndroidRuntime(914): at dalvik.system.NativeStart.main(Native Method)
 E/AndroidRuntime(914): Caused by: java.lang.NullPointerException
 E/AndroidRuntime(914): at br.com.contactsmanager.ContactRepository.listContacts(ContactRepository.java:175)
 E/AndroidRuntime(914): at br.com.contactsmanager.ContactRegister.updateList(ContactRegister.java:39)
 E/AndroidRuntime(914): at br.com.contactsmanager.ContactRegister.onCreate(ContactRegister.java:34)
 E/AndroidRuntime(914): at android.app.Activity.performCreate(Activity.java:5243)
 E/AndroidRuntime(914): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
 E/AndroidRuntime(914): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
 E/AndroidRuntime(914):     ... 11 more

Finally, they follow the codes of Contactrepository and Contactregister.

The project is a schedule of contacts synchronized with that of Android, which will serve as the basis for an application to be developed. I’m new to object-oriented programming.

Contactrepository.java

package br.com.contactsmanager;

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

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteQueryBuilder;
import android.util.Log;
import br.com.contactsmanager.Contact.Contacts;

public class ContactRepository {

    private static final String CATEGORY = "data";

    private static final String DB_NAME = "android_data";

    public static final String TABLE_NAME = "contact";

    protected SQLiteDatabase db;

    public ContactRepository(Context ctx) 
    {

        db = ctx.openOrCreateDatabase(DB_NAME, Context.MODE_PRIVATE, null);

    }

    protected ContactRepository() 
    {

    }

    public long save(Contact contact) 
    {
        long id = contact.id1;

        if (id != 0) {
            update(contact);
        }
        else
        {

            id = insert(contact);
        }

        return id;
    }

    // Insere uma nova pessoa   
    public long insert(Contact contact)
    {
        ContentValues values = new ContentValues();
        values.put(Contacts.NAME, contact.name1);
        values.put(Contacts.LASTNAME, contact.name2);
        values.put(Contacts.PHONE, contact.phone1);

        long id = insert(values);
        return id;
    }

    // Insere uma nova pessoa
    public long insert(ContentValues values)
    {
        long id = db.insert(TABLE_NAME, "", values);
        return id;
    }

    // Atualiza a pessoa no banco. O id da pessoa é utilizado.
    public int update(Contact contact) 
    {
        ContentValues values = new ContentValues();
        values.put(Contacts.NAME, contact.name1);
        values.put(Contacts.LASTNAME, contact.name2);
        values.put(Contacts.PHONE, contact.phone1);

        String _id = String.valueOf(contact.id1);

        String where = Contacts._ID + "=?";
        String[] whereArgs = new String[] { _id };

        int count = update(values, where, whereArgs);

        return count;

    }

    // Atualiza a pessoa com os valores abaixo
    // A cláusula where é utilizada para identificar a pessoa a ser atualizado
    public int update(ContentValues values, String where, String[] whereArgs) 
    {
        int count = db.update(TABLE_NAME, values, where, whereArgs);
        Log.i(CATEGORY, "Updated [" + count + "] registers");
        return count;
    }

    // Deleta a pessoa com o id fornecido
    public int delete(long id) {
        String where = Contacts._ID + "=?";

        String _id = String.valueOf(id);
        String[] whereArgs = new String[] { _id };

        int count = delete(where, whereArgs);

        return count;
    }

    // Deleta a pessoa com os argumentos fornecidos
    public int delete(String where, String[] whereArgs) {
        int count = db.delete(TABLE_NAME, where, whereArgs);
        Log.i(CATEGORY, "Has deleted [" + count + "] registers");
        return count;
    }

    // Busca a pessoa pelo id
    public Contact searchContact(long id) 
    {
        // select * from pessoa where _id=?
        Cursor c = db.query(true, TABLE_NAME, Contact.columns, Contacts._ID + "=" + id, null, null, null, null, null);

        c.moveToFirst ();

        if (c.getCount() > 0) {

            // Posiciona no primeiro elemento do cursor
            //c.moveToFirst ();

            Contact contact = new Contact();

            // Lê os dados
            contact.id1 = c.getLong(0);
            contact.name1 = c.getString(1);
            contact.name2 = c.getString(2);
            contact.phone1 = c.getInt(3);

            return contact;
        }

        return null;
    }

    // Retorna um cursor com todas as pessoas
    public Cursor getCursor() 
    {
        try {
            // select * from pessoas
            return db.query(TABLE_NAME, Contact.columns, Contacts.NAME, null, null, null, null, null); 
        } 
        catch (SQLException e)
        {
            Log.e(CATEGORY, "Error while searching contacts: " + e.toString());
            e.printStackTrace();
            return null;
        }
    }

    // Retorna uma lista com todas as pessoas
    public List<Contact> listContacts() 
        {
        Cursor c = getCursor();

        List<Contact> contacts = new ArrayList<Contact>();

        if ( c.moveToFirst() )
        {

            // Recupera os índices das colunas
            int idxId = c.getColumnIndex(Contacts._ID);
            int idxFirstName = c.getColumnIndex(Contacts.NAME);
            int idxLastName = c.getColumnIndex(Contacts.LASTNAME);
            int idxPhone = c.getColumnIndex(Contacts.PHONE);

            // Loop até o final
            do 
            {
                Contact contact = new Contact();
                contacts.add(contact);

                // recupera os atributos da pessoa
                contact.id1 = c.getLong(idxId);
                contact.name1 = c.getString(idxFirstName);
                contact.name2 = c.getString(idxLastName);
                contact.phone1 = c.getInt(idxPhone);

            } 
            while ( c.moveToNext() );
        }

        return contacts;
    }

    // Busca a pessoa pelo nome "select * from pessoa where nome=?"
    public Contact searchContactByName(String name1) {
        Contact contact = null;

        try {
            // Idem a: SELECT _id,nome,cpf,idade from pessoa where nome = ?
            Cursor c = db.query(TABLE_NAME, Contact.columns, Contacts.NAME + "='" + name1 + "'", null, null, null, null);

            // Se encontrou...
            if (c.moveToNext()) {

                contact = new Contact();

                // utiliza os métodos getLong(), getString(), getInt(), etc para recuperar os valores
                contact.id1 = c.getLong(0);
                contact.name1 = c.getString(1);
                contact.name2 = c.getString(2);
                contact.phone1 = c.getInt(3);
            }
        } catch (SQLException e) {
            Log.e(CATEGORY, "Error while searching person by name: " + e.toString());
            return null;
        }

        return contact;
    }

    // Busca uma pessoa utilizando as configurações definidas no
    // SQLiteQueryBuilder
    // Utilizado pelo Content Provider de pessoa
    public Cursor query(SQLiteQueryBuilder queryBuilder, String[] projection, String selection, String[] selectionArgs,
            String groupBy, String having, String orderBy) 
    {
        Cursor c = queryBuilder.query(this.db, projection, selection, selectionArgs, groupBy, having, orderBy);
        return c;
    }

    // Fecha o banco
    public void close() 
    {
        // fecha o banco de dados
        if (db != null) 
        {
            db.close();
        }
    }

}

----------------------

Contactregister.java

package br.com.contactsmanager;

import java.util.List;

import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import br.com.contactsmanager.Contact.Contacts;

public class ContactRegister extends ListActivity {
    protected static final int INSERT_EDIT = 1;
    protected static final int SEARCH = 2;

    public static ContactRepositoryScript repository;


    private List<Contact> contacts;

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        repository = new ContactRepositoryScript(this);
        updateList();
    }

    protected void updateList() 
    {
        contacts = repository.listContacts();

        setListAdapter(new ContactListAdapter(this, contacts));
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);
        menu.add(0, INSERT_EDIT, 0, "Insert new").setIcon(R.drawable.newcontact);
        menu.add(0, SEARCH, 0, "Search").setIcon(R.drawable.search);
        return true;
    }

    @Override
    public boolean onMenuItemSelected(int featureId, MenuItem item) {

        switch (item.getItemId()) {
        case INSERT_EDIT:

            startActivityForResult(new Intent(this, EditContact.class), INSERT_EDIT);
            break;
        case SEARCH:

            startActivity(new Intent(this, SearchContact.class));
            break;
        }
        return true;
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);
        editContact(position);
    }

    protected void editContact(int position) 
    {
        Contact contact = contacts.get(position);

        Intent it = new Intent(this, EditContact.class);

        it.putExtra(Contacts._ID, contact.id1);

        startActivityForResult(it, INSERT_EDIT);
    }

    @Override
    protected void onActivityResult(int code, int returnCode, Intent it) {
        super.onActivityResult(code, returnCode, it);

        if (returnCode == RESULT_OK) 
        {
            updateList();
        }
    }

    @Override
    protected void onDestroy()
    {
        super.onDestroy();

        repository.close();
    }

}

Answer 1

See the error log, you are referencing a field that does not exist in the table:

03-20 10:35:25.870: E/data(914): Error while searching contacts: android.database.sqlite.SQLiteException: no such column: name (code 1): , while compiling: SELECT _id, name, lastname, phone FROM contact

According to the log, the "name" field does not exist in the "contact" table".

Answer 2

Complementing Philip’s answer: your problem is that the method getCursor - when you find an exception - just log and move on, returning null. When the method listContacts tries to use the cursor, gives the NullPointerException.

To avoid this, either let the exception propagate to the most appropriate point of it being treated, or check on listContacts if the cursor is null before using it.