NullPointerException и я не знаю, почему

Question

я получаю следующее сообщение об ошибке:

06-09 06:56:24.675: E/AndroidRuntime(1629): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gauvion.simpleworkouttracker/com.myapp.MainActivity}: java.lang.NullPointerException 

Logcat говорит свое, вызванные:

06-09 06:56:24.675: E/AndroidRuntime(1629): Caused by: java.lang.NullPointerException 
06-09 06:56:24.675: E/AndroidRuntime(1629):  at com.myapp.MainActivity.onCreate(MainActivity.java:26) 

Вот код для MainActivity:

package com.myapp; 

import android.app.ListActivity; 
import android.database.Cursor; 
import android.os.Bundle; 
import android.support.v4.widget.SimpleCursorAdapter; 
import android.view.Menu; 
import android.widget.Toast; 

public class MainActivity extends ListActivity { 
    private DayDataSource datasource; 
    private SimpleCursorAdapter dataAdapter; 
    private Cursor cursor; 
    private boolean isEditing = false; 
    private Toast toast_deleted; 
    private String[] columns = new String[] { MySQLiteHelper.COLUMN_NAME, MySQLiteHelper.COLUMN_DAY }; 
    private int[] to; 

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

     cursor = datasource.fetchAllDays(); 
     startManagingCursor(cursor); 
     to = new int[] { R.id.listitem_day_name, R.id.listitem_day_day }; 
     dataAdapter = new SimpleCursorAdapter(this, R.layout.listitem_day, cursor, columns, to, 0); 
     setListAdapter(dataAdapter); 
    } 

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

} 

Вот код для DayDataSource:

package com.myapp; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.util.Log; 

public class DayDataSource { 

    private SQLiteDatabase database; 
    private MySQLiteHelper dbHelper; 

    public DayDataSource(Context context) { 
     dbHelper = new MySQLiteHelper(context); 
    } 

    public void open() throws SQLException { 
     database = dbHelper.getWritableDatabase(); 
    } 

    public void close() { 
     dbHelper.close(); 
    } 

    public void createDay(String name, String day) { 
     ContentValues values = new ContentValues(); 
     values.put(MySQLiteHelper.COLUMN_NAME, name); 
     values.put(MySQLiteHelper.COLUMN_DAY, day); 
     database.insert(MySQLiteHelper.TABLE_DAYS, null, values); 
    } 

    public void updateDay(long id, String name, String day) { 
     ContentValues values = new ContentValues(); 
     values.put(MySQLiteHelper.COLUMN_NAME, name); 
     values.put(MySQLiteHelper.COLUMN_DAY, day); 
     database.update(MySQLiteHelper.TABLE_DAYS, values, MySQLiteHelper.COLUMN_ID + " = " + id, null); 
    } 

    public void deleteDay(long id) { 
     database.delete(MySQLiteHelper.TABLE_DAYS, MySQLiteHelper.COLUMN_ID + " = " + id, null); 
    } 

    public Cursor fetchAllDays() { 
     Cursor cursor = database.rawQuery("select " + MySQLiteHelper.COLUMN_ID + ", " + MySQLiteHelper.COLUMN_NAME + ", " + MySQLiteHelper.COLUMN_DAY + " " + 
       "from " + MySQLiteHelper.TABLE_DAYS + " " + 
       "order by case " + MySQLiteHelper.COLUMN_DAY + " " + 
       "when 'Monday' then 0 " + 
       "when 'Tuesday' then 1 " + 
       "when 'Wednesday' then 2 " + 
       "when 'Thursday' then 3 " + 
       "when 'Friday' then 4 " + 
       "when 'Saturday' then 5 " + 
       "when 'Sunday' then 6 " + 
       "when 'No Specific Day' then 7 " + 
       "end", null); 

     if (cursor != null) { cursor.moveToFirst(); } 
     return cursor; 
    } 

} 

Любая помощь будет принята с благодарностью.

Answer 1

вы пытаетесь использовать datasource без инициализации его

cursor = datasource.fetchAllDays(); 

datasource является недействительным в OnCreate