What are Razor Components?

Razor Components, now formally known as Blazor components, are reusable UI building blocks in ASP.NET Core. They allow you to create interactive and dynamic web UIs using C# instead of JavaScript. Think of them as the next generation of ASP.NET Web Forms, but built on modern web standards and offering improved performance and flexibility.

This tutorial delves into understanding Razor Components, their lifecycle, and how to use them effectively in your ASP.NET Core applications.

Core Concept: Reusable UI Elements

Razor Components are encapsulated units of UI. They combine HTML markup, C# code, and styling to create a specific part of the user interface. These components can then be reused throughout your application, promoting code reuse and maintainability.

Basic Razor Component Structure

Let's break down a simple Razor Component:

• @page "/mycomponent": This directive defines the route for this component, making it accessible at /mycomponent.
• HTML Markup: Defines the static parts of the component's UI.
• @currentCount: This is a Razor expression that displays the value of the currentCount variable.
• @onclick="IncrementCount": This binds the IncrementCount method to the button's click event. When the button is clicked, the IncrementCount method is executed.
• @code { ... }: This code block contains the C# logic for the component. Here, we have a field currentCount and a method IncrementCount.

@page "/mycomponent"
<h3>My First Razor Component</h3>

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

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

@code {
    private int currentCount = 0;

    private void IncrementCount()
    {
        currentCount++;
    }
}

Explanation of the Code Snippet

The provided code snippet demonstrates a basic counter component. When the button is clicked, the IncrementCount method is called, which increments the currentCount variable. The Razor engine then re-renders the component to update the UI with the new value of currentCount.

Real-Life Use Case: Creating a Reusable Alert Component

Imagine you need to display alerts throughout your application. You can create a reusable AlertComponent:

• AlertType: A parameter that allows you to specify the type of alert (e.g., "alert-success", "alert-danger").
• ChildContent: A parameter of type RenderFragment. This allows you to pass in any arbitrary HTML content to be rendered within the alert.

To use this component:

@* AlertComponent.razor *@

<div class="alert @AlertType" role="alert">
    @ChildContent
</div>

@code {
    [Parameter]
    public string AlertType { get; set; } = "alert-primary";

    [Parameter]
    public RenderFragment ChildContent { get; set; }
}

Best Practices: Component Parameters and Data Binding

Component Parameters: Use [Parameter] attribute to define properties that can be passed to the component from its parent. This allows for customization and data sharing.

Data Binding: Use @bind-value for two-way data binding between the component and a form element, automatically updating the component's state when the user interacts with the element.

Interview Tip: Understanding Component Lifecycle

Be prepared to discuss the Razor Component lifecycle, including methods like OnInitialized, OnParametersSet, OnAfterRender, and how to use them to perform initialization, data loading, and other tasks at different stages of the component's lifecycle. Understanding when each lifecycle method is called is crucial for correctly managing component state and side effects.

When to Use Razor Components

Use Razor Components when:

• You need reusable UI elements across your application.
• You want to build interactive UIs with C# instead of JavaScript.
• You want to improve code maintainability and reduce code duplication.
• You're building Single Page Applications (SPAs) with Blazor.

Memory Footprint Considerations

While Razor Components offer numerous advantages, it's important to be mindful of their memory footprint, especially in Blazor WebAssembly scenarios. Avoid creating excessive numbers of components or storing large amounts of data within component state. Consider using techniques like virtualization for large lists or implementing data caching strategies to minimize memory usage.

Alternatives to Razor Components

Alternatives to Razor Components include:

• JavaScript Frameworks (React, Angular, Vue.js): Well-established options for building dynamic UIs, but require writing JavaScript code.
• ASP.NET MVC/Razor Pages with JavaScript: A traditional approach that combines server-side rendering with client-side JavaScript for interactivity.
• Web Forms (Legacy): An older technology that is generally not recommended for new development.

Pros of Using Razor Components

• C# Language: Use a single language (C#) for both client-side and server-side development.
• Code Reusability: Build reusable UI components.
• Performance: Blazor WebAssembly provides near-native performance.
• .NET Ecosystem: Access to the vast .NET libraries and tooling.

Cons of Using Razor Components

• Initial Download Size (Blazor WebAssembly): Blazor WebAssembly apps have a larger initial download size compared to traditional web applications.
• Browser Support (Blazor WebAssembly): Requires modern browser support for WebAssembly.
• Debugging (Blazor WebAssembly): Debugging can sometimes be more challenging than with JavaScript frameworks.