how to add column in datagridview when i click the combobox using csharp

public void LoadGridView()
{
   Datatable dt = (Datatale)ViewState("CurrentTable");
   GridView.DataSource = dt;
   GridView.DataBind();
}

protected void combobox_SelectedIndexChanged(object sender, EventArgs e)
{
   Datatable dt = (Datatale)ViewState("CurrentTable");
 
    if(ViewState("CurrentTable")!= null)
    {
       dt = (Datatale)ViewState("CurrentTable");
    }
    else
    {
       dt = new Datattable;
    }
    
    dt.Colums.Add("ComboBoxItems");
    // add combox selected item to datatable object
    dt.Rows.Add(new object[] { combox.SelectedItem.Text });
    
    ViewState("CurrentTable") = dt;
    // call LoadGridView Funcation
    LoadGridView();
}