How Can C# Conditional Compilation Help Target Different Framework Versions?

Use C# conditional compilation to achieve framework targeting

In C# projects, conditional compilation allows developers to conditionally include or exclude code based on preprocessor directives. This technique is useful when targeting different framework versions.

Conditional compilation symbols

The standard conditional compilation symbols for the framework version are:

• NET40
• NET35
• NET20

Integrated conditional compilation

To use conditional compilation, create a #if block and specify the target framework symbol as the condition, as in the following example:

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

Define conditional compilation symbols

By default, Visual Studio sets these symbols based on the target framework selected in the project properties. However, you can define these symbols manually via:

• Project configuration: Add /p:DefineConstants="NET40" parameters to the build command.
• MSBuild: Use conditional $(Framework) == NET20 to set the DefineConstants property in the project file.

Manage different configurations

In order to manage different framework configurations, it is recommended to create build configurations for each target. This allows you to set different project options for each configuration, such as output paths and condition definitions.

Other notes

• Use the Condition attribute on a project file element (e.g. Compile) to conditionally include or exclude files based on the target framework.
• When necessary, use the Condition attribute on the Reference element to exclude the referenced assembly.
• Create an AfterBuild target to compile additional framework versions after the initial build. This ensures that the condition definitions are set correctly for each version.

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