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I am doing a UserControl where anyone can plugin a List.

Internally that List is sorted and programmatically added are the items to a internal ItemaSource.

Anyone who wants to use this UserControl must use the Property ElementsDataSource

public List<T> ElementsDataSource {get;set;}

List<T> is not working/compiling, instead I have to use List<object>.

But then I have to cast the objects inside the ElementsDataSource again to the generic type when I sort them internally and reuse them etc...

How can I offer a generic List Property to my user just like .NET is doing it?

Maybe my user is plugin in a List<Customer> or List<Department> etc... or am I totally wrong and should use List<Object> ?

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    please be explicit: what do you mean it "is not working/compiling"? Commented Nov 26, 2010 at 21:20

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See: Making a generic property

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If my class is a UserControl that will not work: public partial class ElementsView<T> : UserControl => error and I can not declare <T> in xaml ;-)
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If you don't want to make control class generic (this is your List<T> solution) then maybe you should try using List<ISomeInterface> that all classes used with this control implement?

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Note that .NET uses IEnumerable or Object as the type of such a property. It then uses reflection to decide how to process the data.

Instead, you can require that your caller do any sorting or filtering, and just provide you a prepared IEnumerable.

If you need to be able to display a collection of objects, and the collection must be sorted within the control, and the collection must have a "natural" sort order, then the object should implement the IComparable<T> interface. You could then discover this through relection. You would be requiring that the collection implement both IEnumerable<T> and IComparable<T> so that you could do a "natural" sort on the items in the collection.

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Hey John, no the sorting must happen inside the UserControl because the user should not care about that internal process. Just plugin the List<Customer> to the ElementsDataSource , customers are sorted concerning their sortid to be displayed in the UserControl in the proper order!
The sorting would normally be considered an external process if the user control is for the purpose of display. Controls should disply the data provided to them, unless they are changing sort order based on user input: clicking a grid header, for instance. Otherwise, they should just do what they are told to do.
Do not agree because => Its a Must-Feature or a part of that control to display the "elements" in that order, which they got added/saved last time, now reloading them again from database.
This could be a useful feature if the control is very specific to the business use case. I would still place this sorting feature in a separate piece of business-layer code, which would separate the presentation from the business requirements.
Hm... true its business requirement. I will give it more thoughts John, thanks for argueing ;-) but rethink John, this UserControl will be used at 20 places of our application. Should the developer really do 20x sorts on the list and then plug it into the ElementsDataSource? or just plug it and it gets sorted internally ?
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