SQLite数据库获取所有记录NullPointerException

Question

The SQLite Database works fine as far as add/remove a single row until I added the getAllRecords Method and have it run in Oncreate.

I've spent a lot of time fixing it, but no luck.

Can someone please tell me what I am doing wrong?

MySQLite_Database:

    public static final String KEY_ID = "ROW_ID";                   // (0)
    public static final String KEY_ADD_REMOVE = "AddorRemove";      // (1)
    public static final String GROUP_POS = "Group_Position";        // (2)
    public static final String CHILD_POS = "Child_Position";        // (3)
    public static final String DATABASE_TABLE = "Group_Child_Pos_Table";
    public static final String[] ALL_KEYS = new String[] {KEY_ID, KEY_ADD_REMOVE, GROUP_POS, CHILD_POS};

    private static final String POSITION_CREATE_SQL =           
     "CREATE TABLE " + getDatabaseTable() + "("+ 
                                                KEY_ID + " INTEGER PRIMARY KEY," + 
                                                KEY_ADD_REMOVE + " TEXT," + 
                                                GROUP_POS+ " TEXT," + 
                                                CHILD_POS + " TEXT)";   

    private SQLiteDatabase db;
    SQLiteDatabase getWritableDatabase = this.getWritableDatabase();

    public MySQLite_Database(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CHILD_COUNT_CREATE);
        db.execSQL(POSITION_CREATE_SQL);
    }    

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // on upgrade drop older tables
//        db.execSQL("DROP TABLE IF EXISTS " + CHILD_COUNT_CREATE);
        db.execSQL("DROP TABLE IF EXISTS " + POSITION_CREATE_SQL);
        // create new tables
        onCreate(db);       
    }

MainActivity:

private MySQLite_Database MySQLITE_DATABASE;
private SQLiteDatabase  SQLite_database;
private Data_Holder_Class DATA_HOLDER_CLASS;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_expandable_list_view);             

    //Initialize variables here
    MySQLITE_DATABASE = new MySQLite_Database(this);


try {   

Open_SQLITE_DATABASE();
getAllRecords();
}       
catch (Exception e) 
{
   Log.e("ERROR", "ERROROR");
}


public void getAllRecords() {   
Cursor cursor = SQLite_database.query(MySQLite_Database.DATABASE_TABLE, null, null, null, null, null, null);
if(cursor != null)
    {
    while(cursor.moveToNext()){

        String GROUP_POSITION = cursor.getString(cursor.getColumnIndex("GROUP_POS"));
        String CHILD_POSITION = cursor.getString(cursor.getColumnIndex("CHILD_POS"));

        }
    }       

}

Thank you very much

EDIT: posted the working code..

I finally found what I did wrong....

Here is the complete working code. This may help someone else in the future.

BAD CODE:

    public void getAllRecords() {   
    Cursor cursor = SQLite_database.query(MySQLite_Database.DATABASE_TABLE, null, null, null, null, null, null);
    if(cursor != null)
        {
        while(cursor.moveToNext()){

            String GROUP_POSITION = cursor.getString(cursor.getColumnIndex("GROUP_POS"));
            String CHILD_POSITION = cursor.getString(cursor.getColumnIndex("CHILD_POS"));

            }
        }       
 }

to

GOOD CODE:

In MySQLite_Database:

I created this method:

public SQLiteDatabase getWritableData() {
    SQLiteDatabase getWritableDatabase = this.getWritableDatabase();
    return getWritableDatabase;
}

In MainActivity:

MySQLITE_DATABASE = new MySQLite_Database(this);

....

....

public void getAllRecords() {   
Cursor cursor = MySQLITE_DATABASE.getWritableData().query(MySQLite_Database.DATABASE_TABLE, null, null, null, null, null, null);
if(cursor != null)
    {
    while(cursor.moveToNext()){

        String GROUP_POSITION = cursor.getString(cursor.getColumnIndex(MySQLite_Database.GROUP_POS));
        String CHILD_POSITION = cursor.getString(cursor.getColumnIndex(MySQLite_Database.CHILD_POS));

        }
    }       

}

** Basically, in the BAD CODE, I had

private SQLiteDatabase SQLite_database

and used this for the cursor which was wrong. ** The cursor actually needs this instead

SQLiteDatabase getWritableDatabase = this.getWritableDatabase();

}

Thanks to everyone for helping, especially mmlooloo. mmlooloo really helped me catch another mistakes. I hope my mistakes helps someone else.

Answer 1

change these lines:

 String GROUP_POSITION = cursor.getString(cursor.getColumnIndex("GROUP_POS"));
 String CHILD_POSITION = cursor.getString(cursor.getColumnIndex("CHILD_POS"));

to

String GROUP_POSITION = cursor.getString(cursor.getColumnIndex(GROUP_POS));
String CHILD_POSITION = cursor.getString(cursor.getColumnIndex(CHILD_POS));

and

Cursor cursor = SQLite_database.query(MySQLite_Database.DATABASE_TABLE, null, null, null, null, null, null);

to

Cursor cursor = MySQLite_Database.query(MySQLite_Database.DATABASE_TABLE, null, null, null, null, null, null);

Answer 2

I think that you don't specify what columns you want int that line

Cursor cursor = SQLite_database.query(MySQLite_Database.DATABASE_TABLE, null, null, null, null, null, null);

the function query needs:

String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy

and in columns you put null, so you have to specify the columns you want