Can .NET 2.0 assemblies run under .NET 4.0?

5
votes

I have developed a .NET solution that consists of several assemblies, most of which are small helper assemblies that target version 2.0 of the .NET Framework. The remaining assemblies are MVC 3 Web applications, which must necessarily target version 4.0 of the .NET Framework. My solution has no other external dependencies besides the .NET and MVC Frameworks.

My question is the following: When I deploy this solution to customers, do I have to deploy both versions of the .NET Framework, or can I just deploy version 4.0? Can .NET 2.0 assemblies run under .NET 4.0?

4
.netversioning
All three answers are equally valid, but, since I can accept only one, I accepted the one, that was posted first. - pyon

4 Answers

7
votes

Yes, the dependencies embedded in the assembly on .NET 2.0 assemblies are automatically translated to their 4.0 version. But it runs with a version of those assemblies it has never been tested on. They are highly compatible but contain several bug fixes, bugs that you might unknowingly have a dependency on. Nobody can give you a 100% guarantee.

Just try it.

3
votes

You only need the latest version. It's downward compatible.

1
votes

The answer is yes, assemblies developed for .NET 2.0 will run correctly under .NET 4.0

0
votes

Yes and no (at least for .Net 4.5). While it is backwards compatible, the default is to run the code on the associated .Net version as noted here:

The .NET Framework 4.5 and its point releases are backward-compatible with apps that were built with earlier versions of the .NET Framework. In other words, apps and components built with previous versions will work without modification on the .NET Framework 4.5. However, by default, apps run on the version of the common language runtime for which they were developed, so you may have to provide a configuration file to enable your app to run on the .NET Framework 4.5. For more information, see the Version compatibility for apps section earlier in this article.

After adding a MyLovely.exe.config file everything worked fine:

<configuration>
  <startup>
    <supportedRuntime version="v4.0"/>
  </startup>
</configuration>