Can't find the Mistake in my Cursor initialization

Issue

And for a bigger APP project I need to work with an SQLite database. If my code works I don't get any data back. And I think I just don't understand the cursor object. In this code I simply want to get a firstname back but it sasy that my cursor is not initialized correctly, but I got the basic code from Android developers. So I can't figure out why it doesn't work.

public String getVorname (String nachname) {
    SQLiteDatabase db = this.getReadableDatabase();

    String[] projection = {ListeNamen.VORNAME};
    String selection =ListeNamen.NACHNAME+" = ?";
    String[] selectionArgs ={nachname};
    String sortOrder = ListeNamen._ID + " DESC";
    Cursor cursor = db.query(ListeNamen.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);

    cursor.moveToFirst();
    String vorname =cursor.getString(cursor.getColumnIndex(ListeNamen.NACHNAME));
    cursor.close();
    return vorname;
}

I would get back "Jan" as a String but it shows me this Error

java.lang.IllegalStateException: Couldn't read row 0, col -1 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
     at android.database.CursorWindow.nativeGetString(Native Method)
     at android.database.CursorWindow.getString(CursorWindow.java:438)
     at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:51)
     at com.example.mainaplikation.DBHelper.getVorname(DBHelper.java:58)
     at com.example.mainaplikation.MainActivity$1.onClick(MainActivity.java:29)

Solution

With this:

String[] projection = {ListeNamen.VORNAME};

you define the columns that you want the query to select.
So you want only the column ListeNamen.VORNAME.
But with this:

String vorname =cursor.getString(cursor.getColumnIndex(ListeNamen.NACHNAME));

you try to retrieve the column ListeNamen.NACHNAME which does not exist in the results.
By the name of the variable vorname I guess you want to do:

String vorname =cursor.getString(cursor.getColumnIndex(ListeNamen.VORNAME));

but since there is only 1 column in the results, you could also do:

String vorname =cursor.getString(0);

Answered By - forpas