Version independent reference dependencies in managed class libraries

Question

I'm working on an appender for log4net and I'm faced with the problem of how to manage dependencies on the log4net version my class library is built against vs. the actual version deployed on the site. My class library has to reference log4net dlls and as such it becomes tied to the version I'm referencing at built time. However, the sites this component will be deployed will have various log4net versions, some older than mine, some will be newer. How should I approach this problem? I don't want to release a new version of my appender for each log4net new version and place the burden of correctly matching them on my users. I also don't want to ask my appender users to do complex side-by-side manifest tricks. I just want my appender to be simply copied on the end user location and work out-of-the-box with whatever log4net version is present there.

Is this achievable? Am I missing something obvious?

Update:

The only working solution is to use the manifest. I tested with two 'homemade' log4net builds and adding the following configuration section solves my problem:

<runtime>
      <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
         <dependentAssembly>
            <assemblyIdentity name="log4net"
                              publicKeyToken="..."
                              culture="neutral" />
            <bindingRedirect oldVersion="1.2.10.0"
                             newVersion="..."/>
         </dependentAssembly>
      </assemblyBinding>
   </runtime>

where the publicKeyToken is the actual key token of the real log4net assembly, 1.2.10 is the version my appender is built with and the newVersion is the currently deployed version on site. The section can be added to the deployed appconfig or webconfig (it can be done in machine config too, but I rather not recommend that...).

Answer 1

Lot of projects have the same problem that you've just described. As far as I know, this is not something that you as a publisher can control. You can set a publisher policy that allows you to automatically specify that a certain version of your assembly should be used when older versions of your assemblies are referenced, but there is no way to specify this for assemblies that you do not control (like log4net).

On your user side, the administrator can specify that requests for an older version of log4net(which your assembly might reference) by redirected to a specific version via an assembly redirect.

Answer 2

You could handle the AssemblyResolve event:

AppDomain current = AppDomain.CurrentDomain;
current.AssemblyResolve += current_AssemblyResolve;

You could then use string manipulation on the Name property (from the ResolveEventArgs) to remove the version number and load the assembly without specifying its version.