Question

i have a ListActivity to show an Arraylist.
In the onListItemClick() i call another ListActivity.
I have a specific class to extends SQLiteOpenHelper() to manage db.

In the first ListActivity i have this code

protected void onListItemClick(ListView l, View v, int position, long id) {
  String selection = l.getItemAtPosition(position).toString();
  secondListActivity itemsList= new secondListActivity();
  itemsList.showItemsList(selection);
  //Toast.makeText(this, selection, Toast.LENGTH_LONG).show();
}

The showComicsList() method in the secondListActivity have

public void showItemsList(String name)
{
  DatabasesManager databaseHelper = new DatabasesManager(this);
  Cursor series = databaseHelper.getItemsIdByName(name);
  Cursor cursor = databaseHelper.getChildren(series.getString(0));

  for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()) {
    //fetching from database and adding to arrayList
    results.add(cursor.getString(cursor.getColumnIndex(ChildrensTable.NUMBER)));
  }

  cursor.close();

  //display in screen
  this.setListAdapter(
    new ArrayAdapter<Object>(
      secondListActivity.this,
      android.R.layout.simple_list_item_1,
      results
    )
  );
}

the getItemsIdByName() call a cursor

public Cursor getItemsIdByName(String name)
{
  return( getReadableDatabase().query(
  itemsTable.TABLE_NAME, 
  null, 
  "name =" + name,
  null, 
  null,
  null, 
  null, 
  null));
}

When i call the getItemsIdByName() i get this error

09-12 14:12:17.906: ERROR/AndroidRuntime(6090): FATAL EXCEPTION: main
09-12 14:12:17.906: ERROR/AndroidRuntime(6090): java.lang.NullPointerException
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:118)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:187)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at zepod.whatelsecomics.databases.wecDatabasesManager.getComics(wecDatabasesManager.java:159)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at zepod.whatelsecomics.WhatelsecomicsListActivity.showComicsList(WhatelsecomicsListActivity.java:25)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at zepod.whatelsecomics.WhatelsecomicsActivity.onListItemClick(WhatelsecomicsActivity.java:47)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.app.ListActivity$2.onItemClick(ListActivity.java:319)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.widget.AdapterView.performItemClick(AdapterView.java:284)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.widget.ListView.performItemClick(ListView.java:3513)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.widget.AbsListView$PerformClick.run(AbsListView.java:1800)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.os.Handler.handleCallback(Handler.java:587)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.os.Handler.dispatchMessage(Handler.java:92)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.os.Looper.loop(Looper.java:123)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at android.app.ActivityThread.main(ActivityThread.java:3647)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at java.lang.reflect.Method.invokeNative(Native Method)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at java.lang.reflect.Method.invoke(Method.java:507)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
09-12 14:12:17.906: ERROR/AndroidRuntime(6090):     at  dalvik.system.NativeStart.main(Native Method)

Can someone help me?

Answer 1

It’s likely the context on your secondListActivity is not set since you are just instantiating it normally without using startActivity

This is the line that I assume where you are instantiating your second list (where your context is null):

 secondListActivity itemsList= new secondListActivity();

If you follow this stacktrace:

android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)

In the Android source code, you will see that line 203 is

  return mBase.openOrCreateDatabase(name, mode, factory);

Where mBase is the context that you set in SQLiteOpenHelper.

In your code, assuming DatabasesManager is the one who will interact with SQLiteOpenHelper, it is likely this that you pass to it is null

// "this" is possibly null
DatabasesManager databaseHelper = new DatabasesManager(this);
Cursor series = databaseHelper.getItemsIdByName(name);

If you want to use second list in the same Activity, you should consider using the ListView directly in the code without wrapping it using the another ListActivity