Razor Class Libraries (RCL) in ASP.NET Core
💡 Concept Name
Razor Class Library (RCL)
📘 Quick Intro
A Razor Class Library (RCL) allows you to build reusable UI components, views, pages, and static assets in ASP.NET Core and share them across multiple web apps and projects.
🧠 Analogy / Short Story
Think of an RCL as a "UI toolkit" suitcase. You pack buttons, pages, layouts into it, and then carry it into any web app that needs it—no need to recreate the UI every time.
🔧 Technical Explanation
An RCL is a .NET library project that includes Razor files (.cshtml, .razor), C# code, and static assets. It's compiled into a DLL that can be consumed by ASP.NET Core apps. When an app references the RCL, its Razor views and pages are automatically discovered and used.
It’s especially useful for building design systems, component libraries, shared layouts, and partial views. You can even override RCL views in the consuming app.
🎯 Purpose & Use Case
- ✅ Share UI components across multiple ASP.NET Core apps
- ✅ Build internal design systems or theme libraries
- ✅ Avoid duplicating layout or partial views
- ✅ Modularize large applications
- ✅ Publish reusable NuGet packages for UI
💻 Real Code Example
// Create RCL project
dotnet new razorclasslib -n MyApp.UIComponents
// /Pages/Shared/_Header.cshtml in RCL
<div class="header">
<h1>Welcome to MyApp!</h1>
</div>
// _ViewImports.cshtml in consuming app
Highlight: Consuming app gets access to Razor views, partials, and static assets directly from the RCL.
❓ Interview Q&A
Q1: What is an RCL in ASP.NET Core?
A: It’s a reusable Razor-based class library containing UI, pages, or views.
Q2: What file types can be included in RCL?
A: Razor views (.cshtml), Razor components (.razor), static assets, and C# logic.
Q3: Can RCL be published to NuGet?
A: Yes, it’s ideal for reusable packages.
Q4: How to override a Razor view from RCL?
A: Add a view with the same path and name in the main app—it takes precedence.
Q5: Are static files supported in RCL?
A: Yes, placed under wwwroot and configured properly.
Q6: Can RCL include dependency injection services?
A: Yes, via a class like RclStartup or extension method for IServiceCollection.
Q7: What command creates a Razor class library?
A: `dotnet new razorclasslib -n ProjectName`
Q8: Can I use components from an RCL in Blazor?
A: Yes, RCLs are supported in Blazor WebAssembly and Server.
Q9: Where do RCL views reside?
A: Typically under /Areas or /Pages folders.
Q10: What’s the main benefit of RCLs?
A: Encapsulation and reuse of UI and logic across multiple apps.
📝 MCQs
Q1: What does RCL stand for in ASP.NET Core?
- A. Razor Configuration Logic
- B. Razor Class Library
- C. Rendered Code Library
- D. Razor Component Layout
Q2: Which CLI command creates a Razor Class Library?
- A. dotnet new classlib
- B. dotnet new razorclasslib
- C. dotnet generate rcl
- D. dotnet new rcl
Q3: Where should static files be placed in RCL?
- A. /Assets
- B. /wwwroot
- C. /Static
- D. /RclFiles
Q4: Can Razor views from RCL be overridden in main app?
- A. Yes
- B. No
- C. Only with build config
- D. Only if signed
Q5: What type of content can be shared using RCL?
- A. Razor views
- B. Static assets
- C. C# services
- D. All of the above
Q6: Can RCL be used with Blazor?
- A. Yes
- B. No
- C. Only with server-side Blazor
- D. Only in .NET Framework
Q7: What file is used to expose components in RCL?
- A. _GlobalImports.cshtml
- B. _ViewImports.cshtml
- C. _Config.cs
- D. Startup.cs
Q8: Where do you define tag helpers in RCL?
- A. In NuGet metadata
- B. In _ViewImports.cshtml
- C. In Startup.cs
- D. In .csproj
Q9: What is one primary benefit of using RCLs?
- A. Speeds up browser rendering
- B. Promotes code and UI reuse
- C. Prevents runtime errors
- D. Encrypts components
Q10: What extension do Razor components use?
- A. .cshtmlx
- B. .razorhtml
- C. .razor
- D. .component
💡 Bonus Insight
Microsoft’s official ASP.NET Identity UI and the default Blazor UI are implemented using RCLs—proving how powerful and reusable these libraries are in enterprise-level applications.
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