Question

what is the most robust method for adding a empty row (to select “nothing”) to a ListBox?

Sofar i used:

       Dim List = Enumerable.Repeat(New TABLE With {.Text = "", .ID = -1}, 1).AsQueryable().Union(From t In mainctx.TABLEs)
       ddlMangelKategorie.DisplayMember = "Text"
       ddlMangelKategorie.ValueMember = "ID"
       ddlMangelKategorie.DataSource = List.ToList

But this has some drawbacks:

• wordy
• must explicit write the Type (TABLE in this case), so i cant wrap this in a function
• have not found an solution, which works with anonymous types

I.e. if I add a

   From t In mainctx.TABLEs Select Text=col1, id=col2

to the query, this method does not work anymore.

Thanks

Answer 1

Here’s how I would do it using Union (notice that you don’t need Enumerable.Repeat nor AsQueryable).

Dim emptyTable As New TABLE With {.Text = "", .ID = -1}
Dim list = {emptyTable}.Union(mainctx.TABLEs).ToList()
ddlMangelKategorie.DataSource = list

With anonymous types:

Dim emptyTable = New With {.Text = "", .ID = -1}
Dim databaseTables = From t In mainctx.TABLEs 
                     Select Text = t.col1, ID = t.col2
Dim list = {emptyTable}.Union(databaseTables).ToList()
ddlMangelKategorie.DataSource = list