Question

When I try to add an item to the combo box, I get:

“NullReferenceException was unhandled”
“Object reference not set to an instance of an object.”

This happens no matter how I do the code to add to the combobox.

comboBox1.Items.Add("test");

or

try
{
    Parties.Open();
    String test = "SELECT PartyName FROM Parties WHERE PartyID = 4";
    selectParty = new OleDbCommand(test, Parties);
    OleDbDataReader testing = selectParty.ExecuteReader();
    while (testing.Read())
    {
        MessageBox.Show(testing.GetValue(0).ToString());
        comboBox1.SelectedIndex =  comboBox1.Items.Add(testing.GetValue(0).ToString());
    }
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
    return;
}

(messy code above… frustration!)

I’m pretty new to .NET and C# and I don’t understand what is going on here, everything everywhere I go is telling me that my code above should work, but it doesn’t. MSDN simply lists:

comboBox1.Items.Add("Text");

Answer 1

Where are you trying to add items to the ComboBox?

An exception will be thrown if you are calling the above code before InitializeComponent(); in the form constructor. Or if you are assigning the comboBox elsewhere in code.

Make sure all your code is done AFTER InitializeComponent(), this is the method that calls the code in the designer.