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I have the need to make a call to the System.Xaml library in .NET 4.0. Is it possible to make a call to this library if your project is targeted to 3.5?

Jon Seigel
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mrwayne
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    Well, you could compile that other lib as an exe, perhaps add a wrapper to it, and make the two modules communicate through sockets, files, shell ... but that would surely be ugly. – Hamish Grubijan May 03 '10 at 22:36
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    Have a look at the [Reactive Extensions](http://msdn.microsoft.com/en-us/data/gg577609) from Microsoft. It's a kind of backwards compatibility library for 3.5 – David d C e Freitas May 10 '11 at 12:41
  • Possible duplicate of [how to integrate .net library (.dll) from higher version (.net 4) with binaries from lower version (.net 2)](https://stackoverflow.com/questions/4377219/how-to-integrate-net-library-dll-from-higher-version-net-4-with-binaries) – Liam Oct 12 '17 at 12:11

4 Answers4

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No. You'll need to target your project to run in .NET 4, and to use the CLR v4, in order to use .NET 4 assemblies.

On a different note - there is no real advantage here. Just change your application to target .NET 4. If you are going to add a dependency on the .NET 4 framework assemblies, you might as well just target .NET 4 in the first place...

Reed Copsey
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  • The problem is, at the moment i only have VS2008, and i need a particular feature of Xaml (Serialization) in .net 4.0. I was hoping to be able to load it with reflection or something. – mrwayne May 04 '10 at 07:10
  • You can get hold of VS2010 very soon. Re-shuffle the projects' order. – Hamish Grubijan May 04 '10 at 14:07
  • @mrwayne: You can always use VS 2010 Express (available now): http://www.microsoft.com/express/ – Reed Copsey May 04 '10 at 18:18
  • Yeah, unfortunately its a bit more complicated than that, i'm in a work place that would need the entire development team to be upgraded, which means the software needs to be backwards compatibility tested moving to .net 4 ect ect. – mrwayne May 04 '10 at 22:26
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    @mrwayne: If you're working in that type of environment, adding a dep. on .NET 4 is probably not a good idea, either. I'd wait until your company does a full migration to .NET 4. – Reed Copsey May 04 '10 at 23:13
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Here's a kind of Rube Goldberg-esque solution which involves wrapping your .NET 4 DLL methods in COM, and then calling that COM wrapper from .NET 3.5:

https://www.codeproject.com/Articles/204406/How-To-Use-a-NET-Based-DLL-From-NET-Based-Appl

Community
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Matthew Lock
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No, you can't the assembly is mapped differently, one thing that you could do but that's a pain is to create a type in memory that reassembles your net 4.0 dll.

You could use CECIL to get IL instructions.

If you don't know IL very much don't even try to do it.

BartoszAdamczewski
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This question is similar to "how can I use a .NET 2 assembly in .NET 1.x application". It is impossible to add the assembly for new CLR as a reference, but like Hamish pointed out, inter process communication may help.

Lex Li
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