How do I implement a dual listbox against a many to many datasource.

It is fairly straightforward to bind a many-to-many datasource to a conventional listbox or a checkbox list.  Behind the scenes these controls seem to know what has been selected and what has not, allowing for very simple binding.  An example of this is the auto-generated admin section produced by nettiers.

I would like to produce a user control with dual listboxes and arrows to add and remove from the selected list.  I would like to be able to bind as simply as a conventional listbox.

Has anyone done this and can they provide some advice?

I like to use this one.  I have done it a couple times.  I think you get the source code also so you could modify if need be.  It is a good example even if you don't like this control.

http://www.metabuilders.com/Tools/DualList.aspx

jeff

This looks like a great solution.

 I have managed to get the control set up and on the page.  I'm a bit confised though about how I bind to it.  Will I have to modify the control?

Here is my code:

<mbdl:DualList Id="BicSubjectDualList" runat="server"

RightDataTextField="Description" RightDataValueField="BicSubjectId" />

<data:BicSubjectDataSource ID="BicSubjectDataSource" runat="server" SelectMethod="GetAll" />

<data:XrefContactBicSubjectDataSource ID="XrefContactBicSubjectDataSource" runat="server" SelectMethod="GetByContactId">

<asp:QueryStringParameter Name="ContactId" QueryStringField="ContactId" Type="String" />

</Parameters>

<data:ManyToManyListRelationship ID="XrefUserRoleRelationship" runat="server">

<PrimaryMember ID="PrimaryMember1" runat="server"

DataSourceID="ContactDataSource"

EntityKeyName="ContactId" />

<LinkMember ID="LinkMember1" runat="server"

DataSourceID="XrefContactBicSubjectDataSource"

EntityKeyName="ContactId"

ForeignKeyName="BicSubjectId" />

<ReferenceMember ID="ReferenceMember1" runat="server"

DataSourceID="BicSubjectDataSource"

ListControlID="BicSubjectDualList"

EntityKeyName="BicSubjectId" />

</data:ManyToManyListRelationship>

I have basically substituted the DualList for the original Listbox.  I have set the left to my DataSource but I'm not sure how to get the right hand side into and out of the database. 

The control is sitting in a form that is a template.

Gordon

Okay, I have a plan and would like some feedback on it if someone has time.

If I place my dual control, as is, inside a user control and create a property to accept a DataSource, I should be able to wire up the selected and non selected items to the dual list and conversely get that list back out again when I submit the templated form.

My question is, does this sound reasonable?  What is the generic datasource that all "data:BlahDataSources" inherit from?

My confusion arises from not understanding how a list box can bind to a datasource and then use the many-to-many relationship to automatically select the current selections and also post any changes back without a code behind.

I essentialy want to emulate this behaviour with the dual list.

Must I pass my datasource and the m-m relationship or does the m-m relationship alter the datasource and provide some method of determining what has been selected, that I can access, alter and post back?