csproj

  <Target Name="BeforeBuild" Inputs="Hello.ice" Outputs="generated/Hello.cs">
    <Exec Condition="Exists('D:/ZeroC/Ice-3.4.1/slice')" Command="D:/ZeroC/Ice-3.4.1/bin/slice2cs.exe  --Hello.ice" />
  </Target>

 

played around with this approach and it seems the following recipe works also:

1. Add your Slice files to a Visual Studio project and on their properties page assign them a custom Build Action name, e.g. "Slice".
   
2. Add the files to be generated (as empty code files, for instance) and on their properties page assign them a custom Build Action name, e.g. "SliceGenerated".
   
3. Add this <Compile> item in the project file:
   
   Code:

     <ItemGroup>
       . . .
       <Compile Include="@(SliceGenerated)">
         <Visible>False</Visible>
       </Compile>
       . . .
     </ItemGroup>

   The <Visible>False</Visible> tag prevents double display in the Visual Studio IDE.
   
4. Paste this to the end of the project file (part of it copied from ZeroC demo projects):
   
   Code:

     <Target Name="CompileSlice" Inputs="@(Slice)" Outputs="@(SliceGenerated)">
       <Exec Command="%25ICE_HOME%25/bin/slice2cs.exe -I&quot;../slice&quot; --output-dir generated @(Slice->'&quot;%(Identity)&quot;', ' ')" />
     </Target>
     <Target Name="AfterClean">
       <Delete Files="@(SliceGenerated)" />
     </Target>
     <PropertyGroup>
       <CompileDependsOn>
         CompileSlice;$(CompileDependsOn)
       </CompileDependsOn>
     </PropertyGroup>

   This last step requires that ICE_HOME is a defined environment variable, and that the parameters for slice2cs are properly set, like include directories (-I) and output directories ( --output-dir).