Cascading dropDownLists in a repeater. DropDownLists with SQL source code and add / remove

What is the trick for implementing the following interface in ASP.NET?

I think the screenshot should explain everything.

• Both dropDownLists work with SQL tables. [Categories], [Items] related to Category_ID PK / FK
• Number of lines (default 1 line with "Add" button)
• Selecting a category only changes the content of the dropDownList next to it, and the content remains unchanged when other rows are added / removed.
• The "Add" button saves the current setting and adds a new line with "Select a value" or eventually 1st category / 1st selected item

How to keep previously selected categories / items and filtering DropDown by category when adding, modifying, deleting items or some other PostBack on the website?

I tried to use Repeater with DataSet, however I ran into several different problems:

• Failed to save relationship between previous dropDowns
• Droppable DropDowns
• 2nd dropDown plays filtering when new line is added

I can post some code, but since it doesn't work completely, perhaps a completely different approach would be better. I basically started with this tutorial. The repeater currently looks like this:

<repeater>
<itemtemplate>
  <dropDown DataSource="categoriesDS" 
     value='<%# DataBinder.Eval(Container.DataItem, "Category") %>'.../>
  <dropDown DataSource="itemsDS" 
     value='<%# DataBinder.Eval(Container.DataItem, "Item") %>'.../>
  <button CommandName='<%# DataBinder.Eval(Container.DataItem, "Button") %>' 
     Text='<%# DataBinder.Eval(Container.DataItem, "Button") %>' .../>
</itemtemplate>
</repeater>

      

        
        
        
      

    

Thanks in advance for any suggestions or solutions, and I hope this is helpful to others.