title: DevExpress ASPxComboBox SelectItem is null
body: <p>I have an ASPxComboBox which I was able to get filtering correctly on user input. Now I want to save the selected item to the database. But when I try to get the SelectedItem it is null.</p>
  
  <p>ASP</p>
  
  <pre><code>&lt;dxe:ASPxComboBox ID="cboInstructor" runat="server" Width="100%"
              EnableCallbackMode="True" CallbackPageSize="10"
              IncrementalFilteringMode="Contains" ValueType="System.Int32" ValueField="employee_id"
              OnItemsRequestedByFilterCondition="cboInstructor_OnItemsRequestedByFilterCondition_SQL"
              OnItemRequestedByValue="cboInstructor_OnItemRequestedByValue_SQL" TextFormatString="{0} {1}"
              DropDownStyle="DropDown"
          &gt;
              &lt;Columns&gt;
                  &lt;dxe:ListBoxColumn FieldName="display_forename" Caption="Forename" /&gt;
                  &lt;dxe:ListBoxColumn FieldName="display_surname" Caption="Surname" /&gt;
              &lt;/Columns&gt;
          &lt;/dxe:ASPxComboBox&gt;
  
          &lt;asp:SqlDataSource ID="SqlDataSourceInstruct" runat="server" ConnectionString="Server=testserver;User ID=root;Password=password;Persist Security Info=True;Database=central" ProviderName="MySql.Data.MySqlClient" SelectCommand="GetUser" SelectCommandType="StoredProcedure"&gt;
              &lt;SelectParameters&gt;
                  &lt;asp:Parameter Name="filter" Type="String" /&gt;
                  &lt;asp:Parameter Name="startIndex" Type="Int32" /&gt;
                  &lt;asp:Parameter Name="endIndex" Type="Int32" /&gt;
              &lt;/SelectParameters&gt;
          &lt;/asp:SqlDataSource&gt;
          &lt;asp:SqlDataSource ID="SqlDataSourceInstructPopulate" runat="server" ConnectionString="Server=testserver;User ID=root;Password=password;Persist Security Info=True;Database=central" ProviderName="MySql.Data.MySqlClient" SelectCommand="GetUser" SelectCommandType="StoredProcedure"&gt;
          &lt;/asp:SqlDataSource&gt;
  
          &lt;asp:Button ID="btnTest" runat="server" Text="Test" OnClick="btnTest_Click" /&gt;
  </code></pre>
  
  <p>CS</p>
  
  <pre><code>    protected void Page_Load(object sender, EventArgs e)
      {
  
      }
  
      protected void cboInstructor_OnItemsRequestedByFilterCondition_SQL(object source, ListEditItemsRequestedByFilterConditionEventArgs e)
      {
          ASPxComboBox comboBox = (ASPxComboBox)source;
  
          SqlDataSourceInstruct.SelectParameters.Clear();
          SqlDataSourceInstruct.SelectParameters.Add("filter", TypeCode.String, string.Format("%{0}%", e.Filter));
          SqlDataSourceInstruct.SelectParameters.Add("startIndex", TypeCode.Int32, (e.BeginIndex + 1).ToString());
          SqlDataSourceInstruct.SelectParameters.Add("endIndex", TypeCode.Int32, (e.EndIndex + 1).ToString());
          comboBox.DataSource = SqlDataSourceInstruct;
          comboBox.DataBind();
      }
  
      protected void cboInstructor_OnItemRequestedByValue_SQL(object source, ListEditItemRequestedByValueEventArgs e)
      {
          long value = 0;
          if (e.Value == null)
              return;
          if (!Int64.TryParse(e.Value.ToString(), out value))
              return;
          ASPxComboBox comboBox = (ASPxComboBox)source;
          SqlDataSourceInstructPopulate.SelectCommand = @"SELECT employee_id, display_surname, display_forename FROM user_record WHERE employee_id = @ID ORDER BY display_forename";
          SqlDataSourceInstructPopulate.SelectCommandType = System.Web.UI.WebControls.SqlDataSourceCommandType.Text;
          SqlDataSourceInstructPopulate.SelectParameters.Clear();
          SqlDataSourceInstructPopulate.SelectParameters.Add("ID", TypeCode.Int64, e.Value.ToString());
          comboBox.DataSource = SqlDataSourceInstructPopulate;
          comboBox.DataBind();
          comboBox.ValueField = "employee_id";
      }
  
      protected void btnTest_Click(object sender, EventArgs e)
      {
          int iTest = (int)cboInstructor.SelectedItem.GetValue("employee_id");
      }
  </code></pre>
  
  <p>At the line:</p>
  
  <pre><code>int iTest = (int)cboInstructor.SelectedItem.GetValue("employee_id");
  </code></pre>
  
  <p><code>cboInstructor.SelectedItem</code> is null. Anyone have an idea why?</p>