WM_SETFOCUS, where defined for C#?

I need to find out where WM_SETFOCUS is defined. For instance, I know it isn't System.Windows.Forms.WM_SETFOCUS

I've looked online, and everything seems to just use the name with no mention of how to let your compiler know the name.

I DO know the integer value it represents, but I really want to reference an authoritative assembly, and not just litter my code with constants.

I am using the value in a class which implements IMessageFilter.

ADDED DETAILS:

Using IMessageFilter, I am getting messages, and the messages have a Msg field (in开发者_JAVA技巧t) which identifies its type. Where can I find C# definitions of those integer values? (I don't need one named WM_SETFOCUS, I just need something with all the definitions of the values I am receiving.) Since Microsoft supplies IMessageFilter, shouldn't they also supply the information needed to make it useful?

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It would seem to be defined in System.Windows.Forms.NativeMethods.WM_SETFOCUS (Which, unfortunately is an internal class). It's also defined in Microsoft.VisualStudio.NativeMethods.WM_SETFOCUS

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If you're worried about littering your code with native methods, I would do as the framework does and create an internal NativeMethods static class, and dump everything interop-related in it. At least you can keep it all in one place.