How to fill dx combobox depend of another dx combobox

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Gridview

combobox

ASP.NET-Core

Hi everybody... I'm a beginner at asp.net webform, Can you please help me fix my problem? i have dx:ASPxGridView contain of 4 Column "productId","ProductName","Brand",and "Unit". I can get the value for 3 first column, but I need to get the item text for the "Unit" column depend on the productId Combobox column which contains 3 columns "ProductId, ProductNam, Brand". after Combobox changing value.

thank.....

What I have tried:

function OnClick(s, e) {
             var item = listBox.GetSelectedItem();
             memo.SetText(item.GetColumnText(2));
             memo4.SetText(item.GetColumnText(0));
            proId.SetText(item.GetColumnText(0));
            memo2.SetText(item.GetColumnText(1));
            setTimeout(function () { grid.FocusEditor(3); }, 1);

         }

 <dx:ASPxGridView ID="grid" runat="server" AutoGenerateColumns="False"  ClientInstanceName="grid"  OnCellEditorInitialize="grid_CellEditorInitialize" RightToLeft="True" Width="1293px" Theme="Metropolis" >
        <SettingsEditing Mode="Inline">
        </SettingsEditing>
        <Settings ShowFilterRow="True" />
               <SettingsBehavior AllowSelectSingleRowOnly="true" AllowSelectByRowClick="true" />
<SettingsCommandButton>
<ShowAdaptiveDetailButton ButtonType="Image"></ShowAdaptiveDetailButton>

<HideAdaptiveDetailButton ButtonType="Image"></HideAdaptiveDetailButton>
</SettingsCommandButton>
           <Columns>
                 <dx:GridViewDataComboBoxColumn Caption="ProductId" fieldName="ProId" Name="listBox" 
                Visible="true"  VisibleIndex="1">
                                 
                 <PropertiesComboBox  TextField="ProdName"  
                                   ValueField="ProductId"
                       DataSourceID="ProdNumDataSource"
                        ClientInstanceName="listBox">
                                
                          <Columns>
                        <dx:ListBoxColumn Caption="Product Id" FieldName="ProductId" Name="ColProductid"  />
                        <dx:ListBoxColumn Caption="Productc Name" FieldName="ProdName" Name="ColProductName" />
                        <dx:ListBoxColumn Caption="Brand" FieldName="BrandName"  />
                              
                         </Columns>
                         
                </PropertiesComboBox>

                <SettingsHeaderFilter>
                    <DateRangePickerSettings EditFormatString="" />
                </SettingsHeaderFilter>

            </dx:GridViewDataComboBoxColumn>

    <dx:GridViewDataTextColumn Caption="ProductName"  Visible="true" VisibleIndex="2" >

<SettingsHeaderFilter>
<DateRangePickerSettings EditFormatString=""></DateRangePickerSettings>
</SettingsHeaderFilter>

                        <PropertiesTextEdit ClientInstanceName="memo2"></PropertiesTextEdit>
              
                     </dx:GridViewDataTextColumn>
               <dx:GridViewDataTextColumn Caption="Brand" FieldName="brand" VisibleIndex="3">
                   <PropertiesTextEdit ClientInstanceName="memo">
                   </PropertiesTextEdit>
                   <SettingsHeaderFilter>
                       <DateRangePickerSettings EditFormatString="" />
                   </SettingsHeaderFilter>
               </dx:GridViewDataTextColumn>
               <dx:GridViewDataTextColumn Caption="Quantity" FieldName="quantity" VisibleIndex="4">
                  
                   <SettingsHeaderFilter>
                       <DateRangePickerSettings EditFormatString="" />
                   </SettingsHeaderFilter>
               </dx:GridViewDataTextColumn>
                 <dx:GridViewDataComboBoxColumn Caption="Unit" fieldName="Unit" name="memo4"
                Visible="true"  VisibleIndex="5">
                            
                 <PropertiesComboBox  TextField="UnitName" 
                                   ValueField="UnitId"
                       DataSourceID="UnitsDataSource"
                        ClientInstanceName="memo4">
                                 
                          <Columns>
                        <dx:ListBoxColumn Caption="UnitId Id" FieldName="UnitId"  Name="ColProductid" />
                        <dx:ListBoxColumn Caption="UnitName" FieldName="UnitName" Name="ColProductUnit" />
                    </Columns>
                         
                </PropertiesComboBox>

                <SettingsHeaderFilter>
                    <DateRangePickerSettings EditFormatString="" />
                </SettingsHeaderFilter>
  
            </dx:GridViewDataComboBoxColumn>
   </Columns>

       </dx:ASPxGridView>

<asp:SqlDataSource ID="ProdNumDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:phoenixConnectionString %>" SelectCommand="SELECT Products.ProductId, Products.ProdName, Brands.BrandName FROM Products  INNER JOIN Brands ON Products.Brand = Brands.BrandId where ProductId >0">
  </asp:SqlDataSource>
 <asp:SqlDataSource ID="invoice" runat="server" ConnectionString="<%$ ConnectionStrings:phoenixConnectionString %>" SelectCommand="SELECT Bills.AutoDocNum, BillDetails.ProId, BillDetails.quantity, BillDetails.ModuleQuantity, BillDetails.PriceCost, BillDetails.SecondUnit, BillDetails.Unit, BillDetails.module, BillDetails.brand FROM BillDetails INNER JOIN Bills ON Bills.DocNum = BillDetails.DocNum ">
</asp:SqlDataSource>
<asp:SqlDataSource ID="UnitsDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:phoenixConnectionString %>" SelectCommand="SELECT Units.UnitName, ProductsDetail.UnitId, ProductsDetail.productId, ProductsDetail.ItemNo FROM Units INNER JOIN ProductsDetail ON Units.UnitId = ProductsDetail.UnitId">
</asp:SqlDataSource>