How to reference two versions of an API?

Question

I have a need to reference two different versions of the Sharepoint API dll. I have a webservice that needs to run under both Sharepoint 2 and Sharepoint 3, but also needs

Answer 1

This is how I spit out .NET 1.1 versions compiled against WSSv2 API and .NET 2.0 compiled against WSSv3 assembly. It will work for VS 2005 and 2008.

You will need to use MSBEE http://www.codeplex.com/Wiki/View.aspx?ProjectName=MSBee

Working with .NET 1.1 with Visual Studio 2008

Some tips

Open up *.csproj and find out where the SharePoint dll is referenced and change to something like this which changes the referenced assembly depending upon your target (FX1_1 means you are targeting .NET1.1 and therefore WSSv2)

<Reference Include="Microsoft.SharePoint">
  <HintPath Condition="'$(TargetFX1_1)'!='true'">pathto\WSS3\Microsoft.SharePoint.dll</HintPath>
  <HintPath Condition="'$(TargetFX1_1)'=='true'">pathto\WSS2\Microsoft.SharePoint.dll</HintPath>
</Reference>

Use conditional compilation for differences where necessary

#if FX1_1  
    // WSSv2 specific code  
#else  
    // WSSv3 specific code  
#endif

If you get a compiler error but the code looks right it may be that the error is only for .NET1.1 / WSSv2 and compiles fine in .NET2/WSSv3. Check the output tab to see for which target the error occurred

You will also need to master some MSBUILD ninja moves to keep a 1 step build process and keep yourself sane http://brennan.offwhite.net/blog/2006/11/30/7-steps-to-msbuild/ using MSBUILD you can get VS to compile both versions at the same time without resorting to the command line.

This will run the .NET1.1 compilation after .NET has finished and output some messages to the Output window to help you work out where errors occurred.

<Target Name="BeforeBuild">
    <Message Text="--- Building for .NET 1.1 ---" Importance="high" Condition="'$(TargetFX1_1)'=='true'" />
    <Message Text="--- Building for .NET 2.0 ---" Importance="high" Condition="'$(TargetFX1_1)'!='true'" />
</Target>
<Target Name="AfterBuild" Condition="'$(TargetFX1_1)'!='true'">
    <MSBuild Projects="$(MSBuildProjectFile)" Properties="TargetFX1_1=true;" />
</Target>

Answer 2

You could give an "extern alias" a go.

This is one of those times when the VB late binding (option strict off) approach works well. Roll on C# 4.0 and dynamic.

You might try writing an interface for the bits you need (in a base library), and write 2 dlls: one referencing each version of the sharepoint dll. For both projects, implement the interface (throwing NotSupportedException for the bits you can't do), and load the appropriate dll at runtime? (factory approach)

Just try it with a single method before you get too absorbed... don't do the whole thing until you know it works for the simplest of simple methods.