How Can Conditional Compilation Optimize C# Code for Different Framework Targets?

Conditional compilation and target framework optimization of C# code

In C#, conditional compilation can be used to optimize code according to the target framework. Take a look at the following example:

<code class="language-csharp">#if NET40
using FooXX = Foo40;
#elif NET35
using FooXX = Foo35;
#else NET20
using FooXX = Foo20;
#endif</code>

To use this feature, symbols must be defined. One way is to use MSBuild to inject them into the project configuration:

<code class="language-xml">/p:DefineConstants="NET40"</code>

Alternatively, creating a separate build configuration in the project file is a more comprehensive solution:

<code class="language-xml"><PropertyGroup Condition="'$(Framework)' == 'NET20'">
  <DefineConstants>NET20</DefineConstants>
  <OutputPath>bin$(Configuration)$(Framework)</OutputPath>
</PropertyGroup></code>

Additionally, an AfterBuild target can recompile the project for a different version:

<code class="language-xml"><Target Name="AfterBuild">
  <MSBuild Condition="'$(Framework)' != 'NET20'" Projects="$(MSBuildProjectFile)" Properties="Framework=NET20" RunEachTargetSeparately="true" />
</Target></code>

This method ensures that each target framework is correctly defined and allows conditional exclusion or inclusion of specific files and references.

<code class="language-xml"><Compile Condition="'$(Framework)' == 'NET20'" Include="SomeNet20SpecificClass.cs" />
<Reference Condition="'$(Framework)' == 'NET20'" Include="Some.Assembly">
  <HintPath>..\Lib$(Framework)\Some.Assembly.dll</HintPath>
</Reference></code>

By effectively implementing conditional compilation, developers can optimize code and leverage different frameworks to achieve target functionality.

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