support multiple versions of third party library

Question

I created a C# application (MyAppV1) that requires a third party API. My application needs to work with multiple versions of this API, but only a single version at one time. I have setup my solution to change the reference and using statement for different build configurations and I create multiple executable files that each target a different API version.

Presently I have this situation:

• MyAppV1_ThirdPartyV1.exe uses ThirdPartyV1.dll
• MyAppV1_ThirdPartyV2.exe uses ThirdPartyV2.dll
• MyAppV1_ThirdPartyV2_5.exe uses ThirdPartyV2.dll (they didn't change the library name for the minor version of their software)
• MyAppV1_ThirdPartyV3.exe uses ThirdPartyV3.dll

I would like to be able to maintain a list of the versions, perhaps in an App.config and load the appropriate dll library at runtime. I'm having trouble knowing where to begin with this. Is this an appropriate strategy? I'm not sure how best to handle this situation. Multiple versions of my application the only differ with the referenced library seems very clunky to me.

Much of the information I find is related to supporting multiple frameworks, handling the requirement of two versions of the same library downstream at the same time, or needing to load both at the same time. I can't find information on how to handle my particular situation.

Answer 1

This is possible on project level. You can build different configurations in solution and when you add references as below, it will take the desired DLLs

<Choose>  
  <When Condition="'$(Configuration)|$(Platform)'=='YourSpecialConfiguration1|x64'"><!-- attention here -->
    <ItemGroup>
      <Reference Include="your.dllv1.name">
        <HintPath>yourDllPath_v1\your.dllv1.dll</HintPath><!-- attention here -->
        <Private>true</Private>
      </Reference>
      <!-- more references here -->
    </ItemGroup>
  </When>
  <When Condition="'$(Configuration)|$(Platform)'=='YourSpecialConfiguration2|x64'"><!-- attention here -->
    <ItemGroup>
      <Reference Include="your.dllv2.name">
        <HintPath>yourDllPath_v2\your.dllv2.dll</HintPath><!-- attention here -->
        <Private>true</Private>
      </Reference>
      <!-- more references here -->
    </ItemGroup>
  </When>
  <Otherwise>
    <ItemGroup>
      <Reference Include="your.dllname">
        <HintPath>yourRegularPath\your.dllname.dll</HintPath><!-- attention here -->
        <Private>true</Private>
      </Reference>
      <!-- AND more references here -->
    </ItemGroup>
  </Otherwise>
</Choose> 

What you see above - option 1.

Option 2 - Different projects for each version. Downside - if you add a file or reference , you need to add to each project

Option 3 - Add all references but declare different namespace aliases (in reference property window) for each. Then in code do conditional compilation like

ISomething myVar;

#if V1
    myVar = new namespace1.ClassX();
#elif V2
    myVar = new namespace2.ClassX();
#else
    . . . .
#endif

And lastly:

"I would like to be able to maintain a list of the versions, perhaps in an App.config and load the appropriate dll library at runtime."

- you probably don't need non of these. You just need to produce your packages with different versions. Loading at runtime will require more coding work while still supplying all DLLs because you don't know what you going to load next time.