Blazor Interview Questions

Blazor Interview Questions

What is Blazor?

Blazor is a web framework that allows developers to build interactive web UIs using C# instead of JavaScript.

What are the advantages of using Blazor?

Blazor offers advantages like code sharing between client and server, full-stack development in C#, and improved tooling support.

What are the different hosting models in Blazor?

Blazor supports three hosting models: Blazor Server, Blazor WebAssembly, and Blazor Hybrid.

Explain Blazor Server.

Blazor Server is a hosting model for Blazor applications where the application's logic is executed on the server, and the user interface is rendered on the client.

  • Server-Side Execution: Application logic runs on the server.
  • SignalR Connection: Uses SignalR for real-time updates between client and server.
  • Thin Client: Client handles UI rendering and user interactions, reducing client-side workload.
  • Reduced Initial Load: Smaller initial download size, faster load times.
  • Server Resources: Utilizes server resources for processing and maintaining state.
  • State Management: Application state is managed on the server.
  • Network Dependency: Requires a constant network connection.
  • Security: Inherits ASP.NET Core security, keeping sensitive data on the server.
  • Development and Debugging: Easier debugging with .NET tools on the server.

Explain Blazor WebAssembly.

Blazor WebAssembly enables running .NET code directly in the browser, allowing for client-side execution of the app.

What is the difference between Blazor Server and Blazor WebAssembly?

Blazor Server and Blazor WebAssembly are two hosting models for Blazor applications, each with distinct characteristics:

Feature Blazor Server Blazor WebAssembly
Application Logic Runs on the server Runs in the browser
Initial Download Smaller initial download size Larger initial download size
Communication UI updates sent to client over SignalR connection Entire application downloaded to client as WebAssembly
Network Dependency Requires constant connection to server Reduced dependency on server, runs independently on client
Performance Increased network latency, less client-side processing Reduced latency once downloaded, more client-side processing
Offline Support Limited offline support Better offline support once downloaded
Suitable For Real-time updates, applications with network connectivity Offline functionality, complex client-side interactions

How does Blazor Server handle state management?

Blazor Server manages state on the server, reducing the amount of data sent between the client and server.

How does Blazor WebAssembly handle state management?

Blazor WebAssembly handles state management using various methods. Component state is maintained using fields or properties but is reset on re-renders. Cascading parameters allow state sharing down the component tree. State containers (services) enable state sharing across unrelated components, registered typically as singletons. Browser storage (local/session storage) and IndexedDB are used for persistent state across sessions or reloads, accessed via JavaScript Interop. URL query parameters encode state for persistence and sharing. Additionally, Redux-like libraries such as Fluxor can manage complex application state predictably.

What is routing in Blazor?

Routing in Blazor refers to the process of navigating between different pages or components within a Blazor application.

@page "/home"

<h1>Welcome to the Home Page</h1>

How do you implement routing in Blazor?

Routing in Blazor can be implemented using the @page directive or the Router component from the Blazor framework.

  • Define Routes: Specify routes using the @page directive in each component file to determine the URL path associated with that component.
  • Configure Router: Set up routing in the App.razor file by using the Router component, defining how the application will handle different routes and corresponding components.
  • Navigation Links: Create navigation links using the NavLink component, allowing users to navigate between different routes within the application.
  • Program Configuration: Configure the application's entry point in the Program.cs file to set up the Blazor application's environment and dependencies, ensuring proper routing functionality.

What are components in Blazor?

Components in Blazor are reusable building blocks for UI elements, encapsulating both UI and logic.

How do you create a component in Blazor?

Components in Blazor can be created by defining a class with the @code directive and a corresponding .razor file.

  • Define Class: Create a new class inheriting from ComponentBase.
  • Markup File: Create a .razor file with the same name as the class.
  • Add Markup: Write the HTML markup for the component in the .razor file.
  • Code-Behind (Optional): Add C# logic in a separate code-behind file.
  • Use Component: Reference the component's tag name in other Blazor files to use it.

What is the purpose of @code block in Blazor components?

The @code block in Blazor components is used to define the C# code associated with the component, including event handlers and data manipulation logic.

Explain the concept of data binding in Blazor.

Data binding in Blazor allows you to establish a connection between UI elements and data sources, enabling automatic updates when the data changes.

What types of data binding are supported in Blazor?

Blazor supports both one-way and two-way data binding, allowing you to bind data from the component to the UI and vice versa.

<input type="text" @bind="name" />

@code {
    private string name;

How do you perform one-way data binding in Blazor?

One-way data binding in Blazor can be achieved by using the @ symbol followed by the data source or property.

How do you perform two-way data binding in Blazor?

Two-way data binding in Blazor can be achieved using the @bind directive, which binds both the value and the event handler for changes.

  • Bind Property to UI: Use the @bind directive to establish a two-way data binding between a UI element and a C# property within a Blazor component.
  • Automatic Synchronization: Any changes made to the UI element (e.g., input field) by the user automatically update the bound C# property, and vice versa.
  • Simplifies Data Handling: Two-way data binding streamlines data synchronization between the UI and C# code, reducing the need for manual handling of data updates.
  • Example: Binding an input field to a C# property enables seamless interaction, where changes in the input field instantly reflect in the C# property and vice versa, enhancing user experience and developer productivity.
  • Enhanced User Interaction: Two-way data binding facilitates responsive and interactive user interfaces by ensuring that changes made by the user are immediately reflected in the application's state.
  • Efficient Development: By automating the synchronization of data between the UI and C# code, two-way data binding streamlines the development process, enabling developers to focus on building features rather than managing data synchronization manually.

What is dependency injection in Blazor?

Dependency injection in Blazor is a design pattern used to provide instances of dependent objects to components, promoting modularity and testability.

How do you implement dependency injection in Blazor?

Dependency injection in Blazor can be implemented by registering services in the application's service collection and injecting them into components using constructor injection.

  • Service Registration: Register services in Startup.cs or module file.
  • Constructor Injection: Inject services into components via constructor.
  • Utilize Services: Access and use injected services within components.
  • Scoped Lifetime: Consider using scoped lifetime for services when needed.
  • Testing: Simplifies testing by decoupling components from concrete implementations.

What are services in Blazor?

Services in Blazor are reusable components or utilities that provide specific functionality to the application, such as data access or logging.

How do you create and use services in Blazor?

Services in Blazor can be created as classes implementing a specific interface and registered in the application's service collection for use throughout the application.

What is the lifecycle of a Blazor component?

The lifecycle of a Blazor component consists of various stages like initialization, rendering, and disposal, each with corresponding lifecycle methods.

What are the lifecycle methods of a Blazor component?

Blazor components have several lifecycle methods that allow developers to execute code at different stages of a component's lifecycle. Here are the main lifecycle methods:

  • OnInitialized: Invoked when the component is initialized, but parameters have not been set yet.

  • OnParametersSet: Invoked when parameter values are set or changed, allowing the component to react to parameter changes.

  • OnAfterRender: Invoked after the component has been rendered in the browser. It has two variants:

    • OnAfterRender(bool firstRender): Invoked after the initial render and subsequent re-renders. The firstRender parameter indicates whether this is the first render.
    • OnAfterRenderAsync(bool firstRender): Asynchronous variant of OnAfterRender.
  • OnInitializedAsync: Asynchronous version of OnInitialized, allowing asynchronous initialization logic.

  • OnParametersSetAsync: Asynchronous version of OnParametersSet, enabling asynchronous parameter initialization or updates.

  • ShouldRender: Determines whether the component should re-render. By default, it returns true, but you can override it to optimize rendering.

  • OnAfterRenderAsync: Asynchronous variant of OnAfterRender, allowing asynchronous post-render logic.

  • Dispose: Invoked when the component is being disposed of, allowing for cleanup of resources and subscriptions.

How do you handle events in Blazor?

Events in Blazor can be handled by defining event handlers in the component's code block and associating them with UI elements in the markup.

What is event propagation in Blazor?

Event propagation in Blazor refers to the process of passing events from child components to parent components or vice versa.

How do you pass data between components in Blazor?

Data can be passed between components in Blazor using parameters, event callbacks, or by sharing a common state container like a service or a parent component.

  • Parameters: Pass data from parent to child components using parameters.
  • Event Callbacks: Raise events in child components to notify parent components of data changes.
  • Shared State: Share data using a service or a common ancestor component.
  • Choose Method: Select the appropriate method based on component relationship and data flow requirements.

What is the role of Razor syntax in Blazor?

Razor syntax in Blazor allows developers to embed C# code directly into HTML markup, enabling dynamic content generation and logic execution.

What are the advantages of using Razor syntax in Blazor?

The advantages of using Razor syntax in Blazor include improved readability, reduced context switching between markup and code, and enhanced IDE support.

How do you conditionally render content in Blazor?

Content can be conditionally rendered in Blazor using Razor syntax constructs like if statements or the @if directive.

What is the purpose of the @code directive in Blazor?

The @code directive in Blazor is used to define the C# code associated with the component, separating the code from the markup for better organization.

  • Define C# Code: The @code directive allows developers to embed C# code directly within a Blazor component file, facilitating the integration of C# logic with the component's UI markup.

  • Encapsulate Component Logic: By placing C# code within the @code block, developers can encapsulate component-specific logic, such as data manipulation, event handling, and lifecycle methods, directly within the component file.

  • Access Component Parameters and Properties: The @code block provides access to the component's parameters and properties, allowing developers to interact with and manipulate them as needed within the component's C# code.

  • Improve Readability and Maintainability: Embedding C# code directly within the component file enhances code readability and maintainability by keeping related code blocks together in a single location, making it easier to understand and manage component logic.

How do you handle forms in Blazor?

Forms in Blazor can be handled using standard HTML form elements along with event handlers and data binding to manage form submission and validation.

What is form validation in Blazor?

Form validation in Blazor refers to the process of ensuring that user input meets specified criteria before submitting the form, preventing invalid data from being processed.

How do you implement form validation in Blazor?

Form validation in Blazor can be implemented using data annotations, custom validation logic, or third-party validation libraries like FluentValidation.

What are partial classes in Blazor?

Partial classes in Blazor allow developers to split the definition of a class across multiple files, making it easier to manage large and complex components.

How do you use partial classes in Blazor?

Partial classes in Blazor can be created by defining separate parts of the class in different files with the same class name and marking them as partial.

What is the role of layout components in Blazor?

Layout components in Blazor provide a consistent structure and styling for multiple pages or components within the application, promoting code reuse and maintainability.

How do you create and use layout components in Blazor?

Layout components in Blazor can be created by defining a component with the @layout directive and referencing it in other components using the @inherits directive.

What are CSS isolation and how does it work in Blazor?

CSS isolation in Blazor allows developers to scope CSS styles to individual components, preventing style conflicts and making it easier to maintain CSS code.

How do you enable CSS isolation in Blazor components?

CSS isolation in Blazor can be enabled by creating a companion .css file with the same name as the component and adding the :scope selector to target component-specific styles.

  • Create a CSS File: Name it the same as your component but with a .razor.css extension.
  • Define Component-Specific Styles: Write your CSS within this file, targeting elements using classes unique to your component.
  • Apply CSS Classes: Use these classes in your component's markup to style its elements.
  • Build Process: Ensure your build process includes compilation of CSS files. Blazor's default build process supports CSS isolation.

What is the purpose of Razor class libraries in Blazor?

Razor class libraries in Blazor enable the encapsulation and reuse of UI components, pages, and views across multiple applications, promoting code sharing and modularity.

How do you create and consume Razor class libraries in Blazor?

Razor class libraries can be created as separate projects containing Razor components and referenced in Blazor applications like any other .NET class library.

What is JavaScript Interop in Blazor?

JavaScript Interop in Blazor allows developers to call JavaScript functions from .NET code and vice versa, enabling integration with existing JavaScript libraries and APIs.

@code {
    private async Task CallJavaScriptFunction()
        await JSRuntime.InvokeVoidAsync("alert", "Hello from Blazor!");

How do you perform JavaScript Interop in Blazor?

JavaScript Interop in Blazor can be achieved using the IJSRuntime interface to invoke JavaScript functions from .NET code and register .NET methods to be called from JavaScript.

What are the security considerations in Blazor applications?

Security considerations in Blazor applications include protecting against cross-site scripting (XSS) attacks, enforcing authentication and authorization, and securing client-server communication.

How do you implement authentication and authorization in Blazor?

Authentication and authorization in Blazor can be implemented using built-in ASP.NET Core authentication mechanisms like cookies, tokens, or external identity providers such as Azure AD or OAuth.

What is the role of the ComponentBase class in Blazor?

The ComponentBase class in Blazor serves as the base class for all Blazor components, providing essential functionality for rendering, lifecycle management, and event handling.

How do you extend the functionality of Blazor components?

The functionality of Blazor components can be extended by creating custom base classes that inherit from ComponentBase and implementing additional methods or properties as needed.

What are render fragments in Blazor?

Render fragments in Blazor are pieces of UI content defined using Razor syntax that can be passed as parameters to components, enabling dynamic composition of UI elements.

        <p>This content will be rendered inside MyComponent.</p>

@code {
    public RenderFragment ChildContent { get; set; }

How do you optimize performance in Blazor applications?

Performance in Blazor applications can be optimized by reducing unnecessary re-renders, minimizing the size of the application bundle, implementing lazy loading, and using server-side caching where appropriate.