StarBlog Blog Development Notes (12): Razor Page Dynamic Compilation

Series Articles

• Developing a blog project StarBlog based on .NetCore - (1) Why do you need to write your own blog?
• Developing a blog project StarBlog based on .NetCore - (2) Environment setup and creating the project
• Developing a blog project StarBlog based on .NetCore - (3) Model design
• Developing a blog project StarBlog based on .NetCore - (4) Batch import of markdown blogs
• Developing a blog project StarBlog based on .NetCore - (5) Starting to build the Web project
• Developing a blog project StarBlog based on .NetCore - (6) Page development: blog post list
• Developing a blog project StarBlog based on .NetCore - (7) Page development: post detail page
• Developing a blog project StarBlog based on .NetCore - (8) Displaying the category hierarchy
• Developing a blog project StarBlog based on .NetCore - (9) Batch import of images
• Developing a blog project StarBlog based on .NetCore - (10) Image waterfall layout
• Developing a blog project StarBlog based on .NetCore - (11) Implementing visit statistics
• Developing a blog project StarBlog based on .NetCore - (12) Razor page dynamic compilation
• ...

Preface

I haven't updated the blog development notes for a while recently—got lazy = =..

Over the weekend, I polished some detailed features of the blog project and got ready to deploy it live~

This article was originally meant to document the implementation of a few features (theme switching, project monitoring, and a random image API), but while writing pages I found it annoying to have to restart every time I changed a Razor page, so I went through some pitfalls, and that's how this article came about.

Razor Page Dynamic Compilation

Although .Net6 started supporting partial code hot reload, it's still pretty half-baked—I often modify Razor pages but clicking Apply still has no effect~

I'd rather go back to the dynamic compilation that was commonly used before .NetCore3.1~

First, install Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation via NuGet, then configure it in Program.cs

Originally, adding MVC services looked like this

builder.Services.AddControllersWithViews(
    options => { options.Filters.Add<ResponseWrapperFilter>(); }
)

Change it to this (enable dynamic compilation only in development mode)

var mvcBuilder = builder.Services.AddControllersWithViews(
    options => { options.Filters.Add<ResponseWrapperFilter>(); }
);
if (builder.Environment.IsDevelopment()) {
    mvcBuilder.AddRazorRuntimeCompilation();
}

You can also do it without modifying C# code, via an environment variable. Edit the launchSettings.json file and add an environment variable

This way, RuntimeCompilation will be loaded dynamically when the program starts.

"environmentVariables": {
    "ASPNETCORE_ENVIRONMENT": "Development",
    "ASPNETCORE_HOSTINGSTARTUPASSEMBLIES": "Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation"
}

There's also a more thorough approach: don't compile cshtml files when publishing, so you can modify Razor pages after deployment.

Configure it in the project file (xxx.csproj)

<PropertyGroup>
    <RazorCompileOnBuild>false</RazorCompileOnBuild>
    <MvcRazorCompileOnPublish>false</MvcRazorCompileOnPublish>
</PropertyGroup>

This way, when publishing, all Razor views will not be precompiled, and all views will be published together, making it convenient to modify Razor pages in the production environment.

However, note that in a published production environment, modifying view files will not take effect immediately; you need to restart the application (for IIS-hosted environments, you need to restart the site) for the changes to take effect.

You can also configure conditional compilation. For details, see: https://www.cnblogs.com/thinksea/articles/14772837.html

This way, after you modify a Razor page and save, it will automatically recompile, making it convenient to see the effect in real time after changing the page.

Error After Configuring Dynamic Compilation

I ran into a problem here that I hadn't encountered in previous .NetCore3.1 projects

After adding dynamic compilation, the program threw an error on startup

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'source')
   at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Linq.Enumerable.OfType[TResult](IEnumerable source)
   at Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionDescriptorProvider..ctor(IEnumerable`1 pageRouteModelProviders, IOptions`1 mvcOptionsAccessor, IOptions`1 pag
esOptionsAccessor)
   ...省略一大堆报错信息
   at Program.<Main>$(String[] args) in StarBlog\StarBlog.Web\Program.cs:line 96

After searching, I found a Github issues: https://github.com/dotnet/aspnetcore/issues/40609

Do you have the 6.0.201 SDK / 6.0.3 Microsoft.AspNetCore.App runtime installed? Patch builds of packages typically require a corresponding version of the runtime to be installed.

I checked my dotnet SDK version—it's 6.0.101. Looks like an SDK bug; updating the version should fix it~

(Ten minutes later) The update is done, and the problem is indeed solved!

References

• .Net Core 5.0 Razor precompilation, dynamic compilation, and mixed compilation: https://www.cnblogs.com/thinksea/articles/14772837.html
• .NET Hot Reload support for ASP.NET Core: https://docs.microsoft.com/en-us/aspnet/core/test/hot-reload?view=aspnetcore-6.0
• Razor file compilation in ASP.NET Core: https://docs.microsoft.com/en-us/aspnet/core/mvc/views/view-compilation?view=aspnetcore-6.0&tabs=visual-studio
• Can't get RazorPageOptions from DI with version 6.0.3 of Mvc.Razor.RuntimeCompilation: https://github.com/dotnet/aspnetcore/issues/40609