Cook Computing

Barry's MSBuild session on Saturday was the first time I'd studied an MSBuild project file. I was initially puzzled by the existence of multiple <ItemGroup> elements in a project, for example in a C# project file generated by VS2005 where the references are separate from the source files. I wondered whether this had any significance or was possibly just an artefact of the way the file was generated. After some experimentation it seems that the contents of multiple <ItemGroup> elements are treated as if they were in a single <ItemGroup> element. For example, this project:

<Project DefaultTargets="Build"
    xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <Reference Include="System" />
  </ItemGroup>
  <ItemGroup>
    <Compile Include="Program.cs" />
    <Compile Include="Properties\AssemblyInfo.cs" />
  </ItemGroup>
  <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
</Project>

works in the same way as this project:

<Project DefaultTargets="Build" 
    xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <Reference Include="System" />
    <Compile Include="Program.cs" />
    <Compile Include="Properties\AssemblyInfo.cs" />
  </ItemGroup>
  <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
</Project>

Update: Barry posted a follow-up on his blog, describing scenarios in which you could use multiple ItemGroups.