Blazor Component

  • A component in Blazor is an a self-contained chunk of user interface (UI), such as a page, dialog, or data entry form
  • component class is usually written in the form of a Razor markup page with a .razor file extension (components in Blazor are formally referred to as Razor components)
  • Components are .NET classes built into .NET assemblies that:
    • Define flexible UI rendering logic
    • Handle user events
    • Can be nested and reused
    • Can be shared and distributed as Razor class libraries or NuGet packages
  • Razor allows you to switch between HTML markup and C# in the same file with IntelliSense support
  • Unlike Razor Pages and MVC, which are built around a request/response model, components are used specifically for client-side UI logic and composition
  • Links

Single File Approach

  • Markup and logic (C# + HTML) in the same file
  • C# code in @code { ... } block
  • It will eventually become tedious to maintain due to constant scrolling between between markup and logic
  • While a single file approach provides benefits in its simplicity, and is great for small components, it simply doesn’t scale well
  • Avoid for complex component


@page "/counter"


<p>Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    private int currentCount = 0;

    private void IncrementCount()

Code-Behind Approach

Once our component requires complex markup or logic it’s easy to get lost in the large file and/or confused by two different ways of expressing code. Keeping the code and UI separate supports all sorts of best practices

Why Code-Behind?

  • Keep code and presentation separated
  • Use dependency injection
  • Avoid repeating code
  • Loose coupling
  • Scalability

Naming convention:

  • razor file: Foo.razor
  • code behind C# class file: Foo.razor.cs
  • C# class name: class FooBase {...}
  • we are using [componentName]Base for class name because razor markup will be parsed into a component class and we are gonna inherit from code behind class (so, code behind class is base class)

Code behind class is a standard .NET class and inherited by (parsed) razor. Imagine as following

  • .razor is parsed into partial class
  • code behind .cs is partial class
  • resulting class is combination of both and therfore .razor has access to properties in .cs


@page "/counter"
@inherits CounterBase


<p>Current count: @CurrentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>


public class CounterBase: ComponentBase
	protected int CurrentCount { get; set; }

	public void IncrementCount()

Note: Code behind class properties should be protected or public so that razor markup can access them