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Lesson 1376 of 1,90812. Modern Frontend with Razor and BlazorFree lesson

Refactoring Legacy Razor to Blazor

Strategically migrate parts of an MVC application to a Blazor-based architecture.

In this lesson, you will learn how to strategically decompose a monolithic MVC Razor application into modular Blazor components without triggering a full-scale rewrite.

When refactoring legacy Razor views to Blazor, the most common trap is the "all-or-nothing" mentality. Instead, we use the "Island Architecture" strategy. In this approach, you identify specific, high-interaction segments of a legacy Razor page—such as a complex search filter, a dynamic data table, or an interactive form—and encapsulate them into standalone Blazor components.

The Strategy: Hybrid Integration

To begin, you don’t need to remove your Controller or your _Layout.cshtml. You can host Blazor components directly inside your existing Razor views using the Component Tag Helper.

Imagine you have a legacy Index.cshtml that renders a heavy, static report. You want to add a real-time, interactive dashboard widget to the sidebar. Instead of porting the whole page, you create a Blazor component:

<!-- Inside your legacy Index.cshtml -->
<div class="sidebar">
    <component type="typeof(Dashboard.Widgets.RealTimeStats)" 
               render-mode="ServerPrerendered" 
               param-UpdateInterval="5000" />
</div>

Key Considerations

  1. State Sharing: Your legacy MVC app relies on Session or HttpContext.Items, while Blazor operates on an active circuit. When refactoring, move shared data into a scoped service that both the MVC controller and the Blazor component can inject.
  2. Shared Models: Ensure your domain models reside in a common Class Library (.csproj) referenced by both the MVC project and the Blazor project. Avoid duplicating DTOs.
  3. Authentication: If you are using Cookie-based auth in MVC, ensure your App.razor is configured to handle the AuthenticationStateProvider so that your Blazor components can identify the logged-in user seamlessly.

By treating these legacy pages as "hosts" for modern Blazor "islands," you maintain system stability while incrementally migrating logic into a type-safe, component-based environment. This reduces the risk of deployment regressions and allows your team to modernize features one at a time, based on business priority rather than technical debt alone.

Key Takeaway: Use the Component Tag Helper to surgically inject Blazor components into legacy Razor views, allowing for an incremental migration that preserves existing infrastructure while enabling modern interactivity.