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Does GetCustomAttributes() preserve the attribute order in .NET?

Asked 2009-01-26T14:47:53.293
18

The title pretty much says it all. When I'm doing some reflection through my classes, will the MemberInfo.GetCustomAttributes() method preserve the order of attributes on a member, or not? The official documentation does not say anything one way or the other.


In case you're wondering why I would need this, here's the full explanation. It's lengthy and not needed for the question as it is posed now, but perhaps someone can come up with an alternative solution to the greater problem which does not involve relying on attribute enumeration order.

I'm trying to make a flexible framework for an (ASP.NET) application that is expected to have a pretty long lifetime. Over the course it will gain many forms that will have to be accessible from the menu. To make life easier for the developers to come I've made a MenuItemAttribute which you can apply to a form's class. This attribute has an unlimited amount of string parameters in its constructor which allows a developer to specify where exactly will the form reside in the menu. A typical usage example would be something like [MenuItem("Company", "Clients", "Orders")] which would then mean that the menu should have an item "Company" under which there would be an item "Clients" under which there would be an item "Orders" - which would then open the form. A single form can have several of these attributes if needed - it will then be acessible from several places in the menu.

Obviously the whole menu is built in runtime by enumerating through all the classes in my assemblies and searching for this attribute. However recently I've gotten a request that the menu items should be sorted in a predefined way. Forms that have related functionality should be next to each other in the menu. Note that this is NOT alphabetical sorting, but a predefined order that the developers specify.

This then brings the problem - how do I specify the order in these attributes? Since one <

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The lexical ordering of elements in a file is absolutely not guaranteed to be persisted in anyway in the resulting CIL assemblies nor to be respected in the results returned from Reflection. This ordering is not even guaranteed to be the same over repeated calls within the same app domain!

Note that MS have broken this ordering in other parts of reflection in the past (Noting as they did it that this actually caused some issues for some of their code), thus even if it happens to work at the moment there is nothing stopping this breaking in future or on different platforms.

Consider changing your attribute model to allow expressing the semantic information directly rather than relying on ordering.

answered 2009-01-26T15:08:42.393

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