Null propagation feature and Razor views
asp.net-mvc-5, c#, c#-7.0, razor
Solution
It seems you can use C# 6 and C# 7 features indeed, although it needs a little work.
Add these packages:
- `Microsoft.CodeDom.Providers.DotNetCompilerPlatform` (1.0.4 currently)
- `Microsoft.Net.Compilers` (2.1.0 currently)
Make sure you have this section in your `web.config`:
<system.codedom>
<compilers>
<compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.4.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:7 /nowarn:1659;1699;1701" />
<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.4.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+" />
</compilers>
</system.codedom>
And the required imports in your `csproj` file (should be there automatically, but check it):
<Import Project="..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.1.0.4\build\net45\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.props" Condition="Exists('..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.1.0.4\build\net45\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.props')" />
<Import Project="..\packages\Microsoft.Net.Compilers.2.1.0\build\Microsoft.Net.Compilers.props" Condition="Exists('..\packages\Microsoft.Net.Compilers.2.1.0\build\Microsoft.Net.Compilers.props')" />
And this target in it:
<Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild"> ... </Target>
Previous answer:
You can't use that since the ASP.NET MVC Razor view engine doesn't use Roslyn to compile your views. Hence it can't use features available from C# 6 and higher (the null propagation operator = C# 6).
You have to write your code in the pre-C# 6 style, or use another package to take advantage of an alternative view engine, like the one Stack Exchange created (thanks for Marc Gravell to point to that): https://github.com/StackExchange/StackExchange.Precompilation.
According to their documentation, you have to include the package:
Install-Package StackExchange.Precompilation.Build -Pre
and then put this at the end of your `Application_Start` in `Global.asax.cs`:
ViewEngines.Engines.Add(new RoslynRazorViewEngine());
Problem
Hello I have a strange issue. I use the null propagation feature in my razor pages like this ``` @(Model.ligneDossierLie?.dossier_id) ``` my project is based on 4.6.1 Framework and I use the last codeDom compiler 1.0.4 and compiler 2.1.0 In the razor view I have an error message saying that I can't use a C# 6 feature with C#5. But my project is using c#7 .... I roll back to c#6 and it works fine. Is someone know how to use c#7 in this case? Thank you. Web.config ``` <system.codedom> <compilers> <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.4.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701"/> </compilers> </system.codedom> compilerOptions="/langversion:6 ``` was set on 7 and I roll back to 6. After that I didn't had the error anymore, My views are compiling and working correctly