Populate listbox using a class

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Hi
Im trying to populate a lixtbox using a class,I get an error " Object reference not set to an instance of an object"

SQL

//Method to populate listbox in a class
   public DataSet populateAvailableCoursesListBox(int currID)
   {
           dbConnection();
           dbCmd.CommandText = "SELECT DISTINCT courseCode FROM  Courses WHERE currID = @currID;";
           dbCmd.Parameters.AddWithValue("@currID", currID);
           dbAdapter = new OleDbDataAdapter(dbCmd);
           dbAdapter.SelectCommand = dbCmd;
           dbAdapter.Fill(ds);
           dbConn.Close();

           return ds;


   }

C#

//Code behind to populate listbox
   public void populateListbox(int currID)
   {
       dtClass = new DataCls();
       lstCourses.DataSource = dtClass.populateAvailableCoursesListBox(currID);
       lstCourses.Text = "courseCode";
   }

//When the below combobox is clicked it runs the method inside it

C#

protected void cboCurriculums_SelectedIndexChanged(object sender, EventArgs e)
    {
        int currID = Convert.ToInt32(cboCurriculums.SelectedIndex.ToString());
        populateListbox(currID);
    }

Posted 11-Oct-10 21:09pm

Anele Ngqandu

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Brij · Answer 1 · 2010-10-11T21:16:00

As error says, your object is not initialised before getting used. So debug it, you'll get the cause.
and also you list population code of list is not complete. I have done like this.

lstEmployees.DataSource = employess;
lstEmployees.DataTextField = "Name";
lstEmployees.DataValueField = "Id";
lstEmployees.DataBind();

Here employees is a list containing employee objects and Name and Id are the property of the Employee class