Get the select value from a combobox that is bound to a dataset

I want to get the select value from a combobox that开发者_运维知识库 is bound to a dataset.

For binding the combobox I use:

cboEmployees.DataSource = ds.Tables["employees"];
cboEmployees.ValueMember = "employee_number";
cboEmployees.DisplayMember = "employee_name";

To get selected value:

string SelectedValue = cboEmployees.SelectedValue.ToString();

I got this error message: Object reference not set to an instance of an object.

Could anyone help me with this?

Thanks in advance!

you should be setting the cboEmployees.ItemsSource. The reason for the error is because your:

cboEmployees.SelectedValue is null and ToString() method can not be called on it.

EDIT: just thinking about this more and I think should be used like so:

cboEmployees.DataSource = ds.Tables("Employee");
cboEmployees.ValueMember = ds.Tables[0].Columns[0].ToString();
cboEmployees.DisplayMember = ds.Tables[0].Columns[1].ToString();

col[0] is employee number and col[1] would be employee_name

Hope this helps!!!