java.lang.NullPointerException: Attempt to invoke virtual method on a null object reference to select sqlite

Question

I am a newbie of android world. I have a problem of the coding. It was just a tiny error buy i dont know it doesnt work even i change others method but the error still the s

Answer 1

Initialize the DatabaseHelper:

protected void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.surveyinstruction);

    DatabaseHelper db = new DatabaseHelper(this);

    //...
}

Answer 2

I had a similar problem with getId from the database. I found that I was not taking the database from mainAcitivity.java.

    public adapter(Context mCtx, int listLayoutRes, List<employee> employeeList,SQLiteDatabase mDatabase) {
    super(mCtx, listLayoutRes, employeeList);

    this.mCtx = mCtx;
    this.listLayoutRes = listLayoutRes;
    this.employeeList = employeeList;
    this.mDatabase = mDatabase;
}

and using this constructor from mainAcitivity

    adpt= new adapter(this,R.layout.row,employeeList,mdatabase);

solved my problem. I hope this helps.

Answer 3

You have not initialized your reference to DatabaseHelper myDb;. Thats why the nullpointer exception.