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Introduction to Blazor: A Comprehensive Guide to Modern Web Development

This chapter provides a foundational understanding of Blazor, a cutting-edge framework for building interactive web user interfaces. We will explore its core characteristics, project structure, key features, and different rendering modes. This comprehensive guide is designed to equip you with the essential knowledge to begin developing your own Blazor applications.

1. Understanding Blazor

1.1 What is Blazor?

Blazor is a modern front-end web framework that is part of the .NET platform. It leverages HTML, CSS, and C# to enable developers to build rich and interactive user interfaces for web applications.

Front-end Web Framework: A software framework that provides a structure for designing the user interface and user experience of a website or web application. It typically handles the visual presentation and user interactions within the web browser.

A significant advantage of Blazor is its ability to utilize C# for both front-end and back-end development. This allows for a single development stack, where code and logic can be shared between the client and server sides of the application.

Single Development Stack: Refers to using the same programming language and technologies for both the front-end (client-side) and back-end (server-side) development of an application. In Blazor’s case, this stack is based on C# and .NET.

1.2 Key Features of Blazor

  • Component-Based Architecture: Blazor applications are built using reusable UI components.

    Component-Based Architecture: A design approach where applications are constructed from independent, reusable, and encapsulated units called components. Each component manages its own rendering and logic, promoting modularity and maintainability.

    A Blazor component is a self-contained unit of user interface (UI) that encapsulates its rendering logic and event handling. These components can be custom-built or utilize the many built-in components provided by the Blazor framework.

  • Versatile Rendering Modes: Blazor components offer flexibility in rendering, supporting both server-side and client-side rendering. This allows developers to optimize application performance and interactivity based on specific requirements. Components or even entire pages within a single application can be rendered from the server, the client, or a combination of both. We will explore render modes in detail later in this chapter.

  • Beyond Web Applications: Blazor’s capabilities extend beyond traditional web applications. Through a hybrid approach known as Blazor Hybrid, it can be used to build native mobile and desktop applications.

    Hybrid Approach (in application development): A development strategy that combines web technologies (like HTML, CSS, JavaScript, and in Blazor’s case, C# and .NET) with native platform features to build applications that can run on multiple platforms (web, mobile, desktop).

    Blazor Hybrid: A technology that allows embedding Blazor components into native client applications (like mobile or desktop apps). This combines the UI capabilities of Blazor with the native features of the target platform.

2. Setting Up Your First Blazor Project

Let’s walk through creating a basic Blazor Web App project using Visual Studio.

2.1 Creating a New Blazor Project in Visual Studio

  1. Open Visual Studio: Launch Visual Studio.
  2. Create a New Project: Select “Create a new project.”
  3. Choose the Blazor Web App Template: Search for and select the “Blazor Web App” template. This template is specifically designed for building Blazor applications.
  4. Configure Project Settings:
    • Project Name and Location: Choose a name and location for your project. For this initial setup, you can leave the default settings.
    • .NET Version: Ensure you are using .NET 8 (or the latest available version).
    • Interactive Render Mode: The default “Server” render mode is selected. For now, keep this default. We will explore render modes in depth later.
    • Interactivity Location: Leave the default “Per page/component” setting.
  5. Create the Project: Click the “Create” button to generate your Blazor project.

2.2 Running the Default Blazor Application

Once the project is created, Visual Studio will load the project structure. To run the default application:

  1. Start Without Debugging: Click on “Start Without Debugging” in Visual Studio (or press Ctrl+F5).
  2. Observe the Default Application: Your web browser will open, displaying the default Blazor web application. You will see:
    • A “Hello, world!” homepage.
    • A navigation menu on the left, featuring “Home,” “Counter,” and “Weather” pages.
    • A “Counter” page with a button that increments a counter.
    • A “Weather” page displaying boilerplate weather forecast data.

3. Exploring the Blazor Project Structure

Understanding the project structure is crucial for navigating and developing Blazor applications. Let’s examine the key files and folders within a newly created Blazor Web App project.

3.1 Essential Files and Folders

  • *.csproj (Project File): This file, with the .csproj extension, is a fundamental part of any C# based .NET project. It contains project properties and settings that dictate how the project is built and compiled.

    Project File (*.csproj): An XML-based file in .NET projects that describes the project’s configuration, including dependencies, target framework, build settings, and more. It guides the build process.

    Key configurations within the .csproj file include:

    • .NET Version: Specifies the .NET version the project targets (e.g., .NET 8).

    • Nullable Reference Types: Enables or disables nullable reference types, a C# feature for improved null safety.

    • Implicit Usings: Enables implicit namespace imports, automatically including common namespaces based on the project type.

      Namespace: In programming, a namespace is a declarative region that provides a scope to the identifiers (names of types, functions, variables, etc.) inside it, preventing naming collisions and organizing code.

      Implicit Usings (or Global Usings): A C# feature that automatically includes commonly used namespaces in every code file within a project, reducing the need for repetitive using directives at the top of each file.

  • Program.cs (Entry Point): This C# file serves as the entry point of your Blazor application. It is the first code executed when your application starts.

    Entry Point: The starting point of execution for a program. In a .NET web application, Program.cs typically contains the code that sets up the web server, configures services, and starts the application.

    Key functionalities within Program.cs include:

    • Web Application Builder: Uses WebApplication.CreateBuilder() to initialize the web application.

    • Service Configuration: Configures application services, such as Razor components and interactive server components, using builder.Services.

    • Application Building: Builds the web application instance (the app) using builder.Build().

    • Middleware Pipeline: Configures the middleware pipeline for the application.

      Middleware: Software that assembles into an application pipeline to handle requests and responses. It can perform various tasks like routing, authentication, serving static files, and error handling.

      Common middleware configured in Program.cs includes:

      • HTTP to HTTPS Redirection: Redirects HTTP requests to HTTPS for secure communication.

      • Static File Serving: Serves static files like HTML, CSS, JavaScript, and images from the wwwroot directory using app.UseStaticFiles().

        Static Files: Files in a web application that are served to the client’s browser exactly as they are stored on the server, without any server-side processing. Examples include HTML, CSS, JavaScript files, images, and other assets.

      • Cross-Site Request Forgery (CSRF) Protection: Adds middleware to protect against cross-site request forgery attacks.

      • Razor Components Endpoint Mapping: Maps the App component as the root component for Razor components with interactive server rendering using app.MapRazorComponents<App>().

    • Application Execution: Starts the application, making it ready to listen for and handle HTTP requests using app.Run().

  • wwwroot Folder (Static Web Assets): This folder houses static web assets that are directly served to the client’s web browser. It’s the location for files like HTML, CSS, JavaScript, images, and other static content.

    Static Web Assets: Files that are part of a web application and are served directly to the client’s browser without server-side processing. These typically include HTML, CSS, JavaScript, images, and other client-side resources.

  • Properties Folder: Contains project properties and settings.

    • launchSettings.json: Stores settings related to how the application is launched during development. These settings can be modified to suit specific project requirements or different development environments.

  • appsettings.json (Application Configuration): This file holds configuration settings for the application that are intended to be part of the application at runtime.

    Configuration Settings: Parameters and values that control the behavior of an application. These settings can be loaded from configuration files (like appsettings.json), environment variables, or other sources.

    Examples of settings stored in appsettings.json include:

    • Connection strings for databases.
    • Logging levels.
    • Default values for application parameters.
    • Third-party service configurations.

  • appsettings.Development.json (Development Configuration): Stores configuration settings specifically for the development environment. Similar files (e.g., appsettings.Staging.json, appsettings.Production.json) can be created for other environments (staging, production, etc.).

  • Components Folder: This is where all Blazor components of your application reside.

    • App.razor (Root Component): The root component of the application. It contains the root HTML document, the Blazor router, and the Blazor script tags.

      Root Component: The top-level component in a Blazor application, typically named App.razor. It’s responsible for setting up the application’s layout, routing, and other global configurations.

      Router (in Blazor): A component in Blazor that handles navigation within the application. It maps URLs to specific Razor components or pages, enabling client-side routing.

      URL (Uniform Resource Locator): The address of a resource on the internet. In web applications, URLs are used to identify and access different pages or components.

    • Routes.razor (Routing Configuration): Defines the routing configuration for the application. It specifies the mapping between URLs and the corresponding components or pages to render.

      Routing Configuration: The setup that defines how URLs in a web application are mapped to specific handlers, such as components or pages. In Blazor, this is managed by the Router component and defined in files like Routes.razor.

    • Pages Folder: Contains all the pages of your application, each implemented as a Razor component (e.g., Home.razor, Weather.razor, Counter.razor).

    • Layout Folder: Contains layout components that define the overall structure and appearance of your application’s pages.

      Layout Components: Blazor components that define the shared structure and UI elements for a set of pages. They typically include elements like headers, navigation menus, and footers, providing a consistent look and feel across the application.

      • MainLayout.razor: The primary layout component used by the application. It typically defines the overall page structure (header, navigation, footer, etc.).
      • NavMenu.razor: Contains the markup and code for the navigation menu component.

    • _Imports.razor (Global Imports): A special Razor file that contains using directives to import namespaces globally for all Blazor components within the project. This eliminates the need to specify namespaces in each individual component file.

      Using Directives: In C#, using directives are used to import namespaces into a code file, allowing you to use types from those namespaces without fully qualifying their names. In _Imports.razor, these directives apply globally to all Razor components in the project.

4. Blazor Components in Detail

Blazor applications are constructed using components. Let’s delve deeper into what components are and how they function.

4.1 Razor Files and Components

Blazor components are defined in Razor files, which typically have the .razor extension.

Razor File (*.razor): A file format used in Blazor (and ASP.NET MVC) that combines HTML markup with C# code. Razor files are used to define UI components and web pages.

Razor is a markup syntax that blends HTML and C#. It allows developers to embed C# code within HTML to define dynamic rendering logic, such as conditionals and expressions.

Markup Syntax: A system for annotating a document in a way that is syntactically distinguishable from the text. Razor syntax, used in Blazor, allows embedding C# code within HTML markup.

4.2 Pages as Components

Pages in a Blazor application are also Razor components, typically located within the Pages folder. For example, Home.razor defines the homepage.

  • @page Directive: The @page directive at the top of a Razor page component specifies the route for that page. This directive ensures that the component is rendered when a user navigates to the specified route.

    @page Directive: A Razor directive used at the top of a Razor page component to define the route (URL path) that will render this page. For example, @page "/counter" specifies that the component will be rendered when the user navigates to /counter.

    In Home.razor, the @page directive is likely set to /, indicating that it’s the root page of the application.

  • <PageTitle> Component: The <PageTitle> component is a built-in Blazor component used to set the title of the current page, which is displayed in the browser tab.

    <PageTitle> Component: A built-in Blazor component used to set the title of the HTML document, which is typically displayed in the browser tab or window title bar.

4.3 The Counter Component: A Practical Example

The Counter.razor component, found in the Pages directory, demonstrates basic Blazor component functionality.

  • @page Directive: Specifies the route for the counter page (e.g., @page "/counter").

  • @rendermode Directive: The @rendermode directive in Counter.razor enables interactive server rendering. This directive is crucial for making the component interactive, allowing it to handle user events.

    @rendermode Directive: A Razor directive used to specify the rendering mode for a Blazor component or page. It determines where and how the component is rendered (e.g., on the server, on the client using WebAssembly, or both).

    Interactive Server Rendering: A Blazor rendering mode where the component runs on the server, and UI updates and event handling are managed over a real-time connection (like WebSocket) with the browser.

  • Event Handling: The <button> element in Counter.razor has an @onclick attribute. The @onclick event is triggered when the button is clicked.

    @onclick Event: A Blazor event handler attribute that is triggered when a user clicks on an HTML element. It’s used to execute C# code in response to click events.

    The value of the @onclick attribute is set to @IncrementCount, which is a C# method defined in the @code block of the component.

  • @code Block: The @code block in a Razor component is used to write C# code. This block in Counter.razor typically contains:

    @code Block: A section within a Razor component (*.razor file) where you can write C# code. This code can include variables, methods, properties, and other logic that is used by the component.

    • currentCount Field: A C# variable (field) to store the current count value.
    • IncrementCount Method: A C# method that increments the currentCount variable when called (triggered by the @onclick event).

  • Displaying Data: The current count is displayed within a <p> element using C# syntax with the @ symbol (e.g., <p>Current count: @currentCount</p>). This is a basic form of data binding, where the value of the currentCount variable is dynamically displayed in the UI.

4.4 Reusing Components: Adding Counter to the Homepage

Components are reusable. To add the Counter component to the Home.razor homepage, you simply use an HTML-style tag with the component’s name: <Counter />.

4.5 Component Parameters

Components can accept parameters to customize their behavior and appearance.

  • [Parameter] Attribute: To define a component parameter, you create a public C# property in the @code block and decorate it with the [Parameter] attribute.

    [Parameter] Attribute: An attribute in Blazor used to decorate a public property in a component’s @code block, making it a component parameter. This allows you to pass data to the component from its parent component or page.

    In the example, an IncrementAmount parameter of type int is added to the Counter component.

  • Passing Parameter Values: When using a component, you can specify values for its parameters using HTML-style attributes that match the parameter property names. For example, in Home.razor, you can add <Counter IncrementAmount="10" /> to set the IncrementAmount parameter of the Counter component to 10. If no parameter value is specified, the parameter will use its default value (if any is set in the component’s code).

5. Handling User Interface Events

Blazor provides mechanisms for handling various UI events triggered by user interactions.

5.1 Common UI Events

Blazor supports handling a wide range of UI events, including:

  • Click Events: Triggered when an element is clicked (e.g., @onclick).
  • Mouse Events: Triggered by mouse actions like hovering, entering, and leaving elements (e.g., @onmouseover, @onmouseout).
  • Keyboard Events: Triggered when keys are pressed or released (e.g., @onkeydown, @onkeyup).
  • Form Events: Triggered by form interactions like input changes and form submissions (e.g., @oninput, @onsubmit).
  • Focus Events: Triggered when elements gain or lose focus (e.g., @onfocus, @onblur).

5.2 Event Handlers

Event handlers in Blazor are attached to HTML elements or Blazor components using special attributes that start with @on. The attribute name corresponds to the event name (e.g., @onclick, @oninput).

Event Handler: A function or method in code that is executed when a specific event occurs. In Blazor, event handlers are used to respond to user interactions with UI elements.

5.2.1 Example: @onclick Event in Counter.razor

As seen in the Counter.razor component, the @onclick attribute on the <button> element is used to attach the IncrementCount method as an event handler.

5.2.2 Example: @oninput Event for Text Input

The @oninput event is triggered whenever the value of an <input> element changes.

  • Input Element: An <input type="text" /> element is used to create a text input field.

  • @oninput Attribute: The @oninput attribute is added to the <input> element to handle input changes.

  • Event Handler Method: A C# method (e.g., HandleInput) is created to process the @oninput event. The method is assigned as the value of the @oninput attribute: @oninput="HandleInput".

  • ChangeEventArgs Argument: Event handler methods for input events often receive a ChangeEventArgs argument. This argument provides information about the event, such as the new value of the input.

    ChangeEventArgs: An event argument type in Blazor that is used with input events like @oninput. It provides information about the event, including the new value of the input element.

    To access the input value from the ChangeEventArgs, you can use args.Value. Since args.Value is of type object?, you may need to cast it to a string (e.g., (string)args.Value) and handle potential null values.

  • Lambda Expressions for Simple Event Handlers: For simple event handling logic, you can use lambda expressions directly within the event attribute. For example, you could increment currentCount directly in the @onclick attribute using a lambda expression: @onclick="@(() => currentCount++)".

    Lambda Expression: A concise way to define anonymous functions (functions without a name) in C#. They are often used for short, inline event handlers in Blazor.

5.2.3 Example: @onmouseover Event for Mouse Hover

The @onmouseover event is triggered when the mouse cursor moves over an element.

  • @onmouseover Attribute: Add the @onmouseover attribute to an element (e.g., a <div>).

  • Event Handler Method: Create a method (e.g., HandleMouseOver) to handle the @onmouseover event. Assign this method as the value of the @onmouseover attribute: @onmouseover="HandleMouseOver".

  • MouseEventArgs Argument: Event handlers for mouse events receive a MouseEventArgs argument, providing information about the mouse event (e.g., mouse coordinates).

    MouseEventArgs: An event argument type in Blazor that is used with mouse events like @onmouseover, @onmouseout, @onmousemove, etc. It provides information about the mouse event, such as mouse coordinates and button states.

5.2.4 Example: @onkeydown Event for Keyboard Input

The @onkeydown event is triggered when a key is pressed down while an element has focus.

  • @onkeydown Attribute: Add the @onkeydown attribute to an element (e.g., an <input> or <div>).

  • Event Handler Method: Create a method (e.g., HandleKeyDown) to handle the @onkeydown event. Assign this method as the value of the @onkeydown attribute: @onkeydown="HandleKeyDown".

  • KeyboardEventArgs Argument: Event handlers for keyboard events receive a KeyboardEventArgs argument, providing information about the keyboard event, such as the key pressed.

    KeyboardEventArgs: An event argument type in Blazor that is used with keyboard events like @onkeydown, @onkeyup, @onkeypress. It provides information about the keyboard event, such as the key that was pressed or released.

    To get the value of the key pressed, use the args.Key property from the KeyboardEventArgs.

5.2.5 Example: @onfocus and @onblur Events for Focus Management

  • @onfocus Event: Triggered when an element gains focus (e.g., when an input field is clicked).

  • @onblur Event: Triggered when an element loses focus (e.g., when clicking outside an input field).

    • @onfocus and @onblur Attributes: Add these attributes to an element (e.g., <input>).

    • Event Handler Methods: Create methods (e.g., HandleFocus, HandleBlur) for each event. Assign these methods as values to the respective attributes: @onfocus="HandleFocus" and @onblur="HandleBlur".

    • FocusEventArgs Argument: Event handlers for focus events receive a FocusEventArgs argument.

      FocusEventArgs: An event argument type in Blazor that is used with focus events like @onfocus and @onblur. It provides information about the focus event.

6. Data Binding in Blazor

Data binding is a fundamental concept in Blazor that connects the application’s UI to underlying data sources. It enables synchronization between the UI and data, ensuring a responsive and dynamic user experience.

Data Binding: A technique in UI frameworks that establishes a connection between the UI elements (like text boxes, labels) and data properties in the application’s code. Changes in the data automatically update the UI, and vice versa, depending on the type of binding.

6.1 One-Way Data Binding

One-way data binding occurs when data flows in a single direction, typically from the C# code to the UI. It is primarily used to display data in the UI.

One-Way Data Binding: A type of data binding where data flows in only one direction, typically from the data source (e.g., C# code) to the UI. Changes in the data source update the UI, but changes in the UI do not automatically update the data source.

One-way data binding is achieved using the @ symbol in Razor syntax to display the value of a C# variable or expression in the HTML markup (e.g., <p>Value: @text</p>).

6.2 Two-Way Data Binding

Two-way data binding allows data to flow in both directions: from the C# code to the UI and from the UI back to the C# code. This means that changes made in the UI (e.g., typing in an input field) automatically update the corresponding C# variable, and changes in the C# variable update the UI.

Two-Way Data Binding: A type of data binding where data flows in both directions between the data source and the UI. Changes in either the data source or the UI automatically update the other, maintaining synchronization.

Two-way data binding in Blazor is primarily achieved using the bind attribute.

bind Attribute: A Blazor attribute used for two-way data binding. It’s typically applied to input elements (like <input>, <select>, <textarea>) to bind their value to a C# property.

  • @bind Attribute Usage: To implement two-way data binding, use @bind="propertyName" on an input element, where propertyName is the name of a C# property in your component’s @code block. For example: <input type="text" @bind="text" />.

6.3 Binding Events: Controlling Binding Behavior

By default, the @bind attribute updates the bound property on the change event of the input element. However, you can customize the binding event using the bind:event syntax.

  • bind:event Attribute: This attribute allows you to specify the event that triggers the data binding update. For example, @bind:event="oninput" will update the bound property on every input event (i.e., with each keystroke).

    bind:event Attribute (or bind-event): An extension to the @bind attribute in Blazor that allows you to specify the UI event that triggers the data binding update. For example, bind:event="oninput" updates the bound property on every input event.

6.4 bind:after Attribute: Executing Code After Binding

The bind:after attribute allows you to specify a C# method to be executed immediately after the data binding occurs. This is useful for performing actions that should happen after a property is updated due to user input, such as triggering a search or validation.

bind:after Attribute (or bind-after): An extension to the @bind attribute in Blazor that allows you to specify a C# method to be executed immediately after the data binding process is complete. This is useful for triggering actions that should occur right after a bound property is updated.

  • bind:after Attribute Usage: Use @bind:after="methodName" along with the @bind attribute, where methodName is the name of a C# method in your component’s @code block. For example: <input type="text" @bind="searchText" @bind:after="Search" />.

7. Blazor Render Modes: Understanding Interactivity

Blazor offers different render modes that determine where and how components are rendered, impacting interactivity and performance.

Render Mode: In Blazor, a setting that dictates where and how a component is rendered: either on the server, on the client (using WebAssembly), or initially on the server and then switching to the client. Render modes significantly impact application interactivity, performance, and resource usage.

7.1 Static Server-Side Rendering

  • Default Render Mode: By default, Blazor components are statically rendered from the server.

  • Process: When a request is routed to a component, the server renders the HTML for the component and sends it as a response to the browser.

  • No Interactivity: In static server-side rendering, no state is maintained on the server, and there is no active connection with the browser after the initial HTML is sent. Components rendered in this mode are non-interactive, meaning they cannot directly handle UI events from users.

  • Use Cases: Static components are suitable for scenarios where you only need to display static content and do not require user interaction (e.g., displaying blog posts, informational pages).

  • Enhanced Navigation: Blazor enhances page navigation in static server-side rendering. Enhanced navigation intercepts navigation requests and performs fetch requests to the server, updating only the necessary parts of the DOM without full page reloads.

    Enhanced Navigation (in Blazor): A feature that improves the user experience in Blazor applications by intercepting navigation requests and updating only the changed portions of the page, rather than performing full page reloads. This makes navigation feel faster and smoother.

    Fetch Request: A web API that allows web browsers to make HTTP requests to servers to retrieve resources or submit data. In enhanced navigation, Blazor uses fetch requests to get updated content from the server.

    DOM (Document Object Model): A programming interface for HTML and XML documents. It represents the page structure as a tree of objects. Blazor updates the DOM to reflect changes in the UI.

  • Enhanced Form Handling: Similarly, enhanced form handling can be optionally enabled for forms within statically rendered components. It works in a similar way to enhanced navigation by using fetch requests for form submissions.

    Enhanced Form Handling (in Blazor): A feature that improves form submissions in Blazor applications by intercepting form submissions and using fetch requests to communicate with the server. This allows for partial page updates and a smoother user experience compared to traditional full form postbacks.

7.2 Streaming Rendering

  • Purpose: Streaming rendering is designed for scenarios where parts of a web page or component can be rendered as data becomes available from the server, especially when long-running asynchronous tasks are involved (e.g., fetching data from an API or database).

    Streaming Rendering: A rendering technique where the server sends HTML content to the client in chunks or streams as it becomes available, rather than waiting for the entire page to be rendered before sending anything. This improves perceived loading times, especially for pages with long-running tasks.

  • Process: The server starts sending HTML content to the client as soon as it’s ready, without waiting for the entire page or component to be fully rendered.

  • Placeholder Content: Often, placeholder content (e.g., “Loading…”) is displayed to the user while waiting for the rest of the content to load.

  • Example: Weather Page: The default Blazor Weather page demonstrates streaming rendering. You might see a “Loading…” message initially, followed by the weather forecast data once it’s fetched from the server (simulated in the example).

  • @attribute [StreamRendering]: To enable streaming rendering for a component, you can add the @attribute [StreamRendering] directive at the top of the Razor file.

7.3 Interactive Render Modes: Enabling User Interaction

To create fully interactive Blazor components that can handle UI events from the browser, you need to use interactive render modes. Blazor provides three primary interactive render modes:

7.3.1 Interactive Server Rendering

  • Communication via WebSocket: Interactive server rendering manages UI events on the server via a WebSocket connection with the browser.

    WebSocket: A communication protocol that provides full-duplex (bidirectional), persistent connection between a client (like a web browser) and a server over a single TCP connection. It’s used in Blazor’s interactive server rendering to enable real-time communication for UI updates and event handling.

  • Process:

    1. UI events (e.g., button clicks) are transmitted from the browser to the server through the WebSocket connection.
    2. Blazor on the server processes the event and updates the component’s state.
    3. The server renders the updated component and sends the DOM diff (changes) back to the browser via the WebSocket connection.
    4. The browser applies the DOM diff to update the UI.

  • Server Dependency: Interactive server rendering requires a persistent, active connection between the browser and the server.

  • Potential Latency: Network latency can affect the responsiveness of the UI, as every user interaction requires communication with the server.

  • Server Resources: Maintaining WebSocket connections for each user can increase server resource usage, especially with a large number of concurrent users.

  • Enabling Interactive Server Rendering: Use the @rendermode InteractiveServer directive at the top of a Razor component or page to enable interactive server rendering.

7.3.2 Interactive WebAssembly Rendering

  • Client-Side Execution: Interactive WebAssembly rendering executes the component’s code directly in the browser using a WebAssembly-based .NET runtime.

    WebAssembly (Wasm): A binary instruction format for a stack-based virtual machine. Web browsers can execute WebAssembly code at near-native speed. Blazor WebAssembly uses this to run .NET code directly in the browser.

  • Process:

    1. When the application is first loaded, the .NET runtime and application code are downloaded to the browser.
    2. The component runs entirely client-side within the browser’s WebAssembly environment.
    3. UI events are handled directly in the browser, and UI updates are rendered locally without server communication for each interaction.

  • Initial Load Time: Interactive WebAssembly rendering typically has a longer initial load time as the .NET runtime and application code need to be downloaded. However, these are cached by the browser for subsequent visits.

  • Client-Side Resources: The workload is offloaded to the client’s browser, reducing server load.

  • No Server Connection Required (After Initial Load): Once the application is loaded, no continuous server connection is needed for UI interactions.

  • Enabling Interactive WebAssembly Rendering: Use the @rendermode InteractiveWebAssembly directive to enable interactive WebAssembly rendering.

7.3.3 Interactive Auto (Auto) Rendering

  • Hybrid Approach: Interactive Auto render mode combines the benefits of interactive server rendering and interactive WebAssembly rendering.

    Interactive Auto (Auto) Rendering: A Blazor render mode that initially renders a component on the server (like interactive server rendering) for faster initial load, and then switches to client-side rendering using WebAssembly in the background. This aims to provide a balance between initial load speed and subsequent interactivity.

  • Process:

    1. Initial Server Rendering: The component is initially rendered on the server (like interactive server rendering) for faster initial page load.
    2. Background WebAssembly Download: In the background, the .NET WebAssembly runtime and the client-side part of the application are downloaded to the browser.
    3. Automatic Switch to WebAssembly: Once the download is complete, the component automatically switches to WebAssembly-based rendering for future interactions.

  • Benefits:

    • Faster Initial Load: The initial page load is faster as the component is initially rendered on the server.
    • Subsequent Client-Side Interactivity: After the initial load and WebAssembly download, the component becomes fully interactive client-side, similar to interactive WebAssembly rendering, without requiring constant server communication.

  • Initial Server Dependency (Temporary): There is an initial dependency on the server for the first render, but this dependency is removed once the switch to WebAssembly rendering is complete.

  • Enabling Interactive Auto Rendering: Use the @rendermode InteractiveAuto directive to enable interactive Auto rendering.

7.4 Project Setup for Interactive Render Modes

To explore interactive WebAssembly and Auto render modes effectively, you can create a new Blazor Web App project and choose “Interactive Auto (Auto)” as the interactivity type during project creation. This project template is configured to support both server-side and client-side rendering.

  • Project Structure with Client Project: When you create a Blazor Web App with interactive Auto or WebAssembly rendering, the solution structure typically includes two projects: a server project and a client project.
    • Server Project: Contains server-side code and components, similar to previous Blazor Web projects.
    • Client Project: Contains code and components that will be downloaded to the browser and run client-side using WebAssembly. Components intended to run in WebAssembly are placed in the client project.
  • Interactivity Location (Per page/component vs. Global): When creating a Blazor Web App, you can choose the interactivity location:
    • Per page or component: Interactivity is configured individually for each page or component using the @rendermode directive.
    • Global: Interactivity is set globally for the entire application. In this case, all components will use the same render mode (e.g., interactive Auto).
    • For finer control and optimization, “Per page/component” interactivity is generally recommended.

8. CRUD Operations in Blazor: Building Data-Driven Applications

CRUD stands for Create, Read, Update, and Delete. These are the fundamental operations for managing data in most applications. This section explores how to implement CRUD operations in Blazor applications.

CRUD (Create, Read, Update, Delete): An acronym representing the four basic operations that are performed on data in persistent storage: Create (add new data), Read (retrieve existing data), Update (modify existing data), and Delete (remove data).

8.1 Setting Up a Blazor Project for CRUD Operations

  1. Create a New Blazor Web App Project: Create a new Blazor Web App project, choosing “Interactive Server Rendering” for interactivity.

  2. Define a Data Model: Create a C# class to represent the data you want to manage. This class will serve as your data model. For example, a Student class with properties like ID, Name, Age, and Birthday. Place this model class in a Models folder within your project.

  3. Add a Database Context: Create a DB context class using Entity Framework Core. This class will manage the connection to your database and provide access to your data models.

    DB Context (Database Context): In Entity Framework Core (EF Core), a DB context is a class that represents a session with the database. It’s used to query and save data, manage connections, and perform database operations.

    • Install the necessary NuGet packages for Entity Framework Core (e.g., Microsoft.EntityFrameworkCore.SqlServer, Microsoft.EntityFrameworkCore.Tools).
    • Create a class that inherits from DbContext (from Microsoft.EntityFrameworkCore).
    • Define a DbSet<YourModel> property for each data model you want to manage in the database.
    • Configure the database connection string in your appsettings.json file.

  4. Scaffolding CRUD Pages: Blazor provides scaffolding tools to automatically generate Razor components for CRUD operations based on your data model and DB context.

    • Right-click on the Pages folder in your project.
    • Select “Add” -> “New Scaffolded Item…“.
    • Choose “Razor Component” from the left menu.
    • Select “Razor Component using Entity Framework (CRUD)” in the main panel and click “Add”.
    • In the “Add Razor Component using Entity Framework (CRUD)” dialog:
      • Model Class: Select your data model class (e.g., Student).
      • DbContext Class: Select your DB context class.
      • Click “Add”.

    This scaffolding process will generate Razor components for:

    • Create: A page to create new records (Create.razor).
    • Read (Index): A page to list and view records (Index.razor).
    • Read (Details): A page to view details of a single record (Details.razor).
    • Update (Edit): A page to edit existing records (Edit.razor).
    • Delete: A page to delete records (Delete.razor).

  5. Create a Database: Use SQL Server Management Studio or Visual Studio’s Server Explorer to create a new SQL Server database.

  6. Update Connection String: In appsettings.json, replace the placeholder connection string with the connection string for your newly created database.

  7. Add Migrations and Update Database: Use Entity Framework Core migrations to create the database schema based on your data model.

    • Open the Package Manager Console in Visual Studio (Tools -> NuGet Package Manager -> Package Manager Console).
    • Run the command Add-Migration InitialCreate (or a descriptive name for your initial migration).
    • Run the command Update-Database to apply the migrations and create the database tables.

8.2 Understanding the Generated CRUD Components

8.2.1 Index Page (Index.razor)

  • Route: Typically set to /students (or a similar route based on your model name).

  • Functionality: Displays a list of records from your data model in a table.

  • QuickGrid Component: Uses the QuickGrid component to display data in a tabular format.

    QuickGrid Component: A built-in Blazor component designed for displaying data in a grid or table format. It offers features like sorting, filtering, and pagination and can efficiently handle large datasets.

    • Items Attribute: The Items attribute of the QuickGrid is bound to the data source (e.g., DbContext.Students.ToList()).
    • PropertyColumn Components: <PropertyColumn> components are used to define each column in the table, specifying which property of the data model to display in each column.
    • TemplateColumn Component: A <TemplateColumn> is used for the last column, which contains links to “Edit,” “Details,” and “Delete” pages for each record. These links are constructed using the record’s ID.
    • Formatting Columns: You can use the Format attribute of <PropertyColumn> to format data display (e.g., formatting a DateTime property to display only the date part). You can also use the Type property to change the column header text.

8.2.2 Create Page (Create.razor)

  • Route: Accessed via a link from the Index page (e.g., “Create New”).

  • Functionality: Provides a form to create new records.

  • EditForm Component: Uses the EditForm component to handle form submission and data binding.

    EditForm Component: A Blazor component designed for creating and editing forms. It simplifies form handling, validation, and data binding to a model.

    • Model Attribute: The Model attribute of the EditForm is bound to an instance of your data model (e.g., a new Student object).

    • OnValidSubmit Attribute: The OnValidSubmit attribute is set to a C# method (e.g., AddStudent) that will be executed when the form is submitted successfully (after validation).

    • FormName Attribute: The FormName attribute is used to uniquely identify the form, especially in cases where you have multiple forms on the same page.

    • Enhanced Attribute: The Enhanced attribute is often enabled to enhance form handling with fetch requests, similar to enhanced navigation.

    • Input Components: Input components like <InputText>, <InputNumber>, and <InputDate> are used to create form fields for each property of the data model. The bind-Value attribute of these input components is used for two-way data binding to the corresponding properties of the model.

    • Validation Components:

      • DataAnnotationsValidator: Adds support for data annotations-based validation (using attributes like [Required], [Range]) defined in your data model class.

        Data Annotations Validator: A Blazor component that enables client-side and server-side validation based on data annotation attributes (e.g., [Required], [StringLength], [Range]) applied to properties in your data model class.

      • ValidationMessage Component: Displays validation error messages for individual form fields.

        ValidationMessage Component: A Blazor component that displays validation error messages associated with a specific form field. It typically appears next to the input field it’s related to.

      • ValidationSummary Component: Displays a summary of all validation errors for the form.

        ValidationSummary Component: A Blazor component that displays a summary of all validation errors for the entire form. It’s typically placed at the top of the form to provide an overview of validation issues.

    • Data Annotations in Model: To enable validation, you can add data annotations attributes to the properties of your data model class. These attributes define validation rules (e.g., [Required], [Range]).

8.2.3 Edit Page (Edit.razor)

  • Route: Accessed via the “Edit” link from the Index page, typically including the record’s ID in the URL (e.g., /students/edit/{id:int}).

  • Functionality: Provides a form to edit existing records.

  • EditForm Component: Uses the EditForm component, similar to the Create page.

  • Data Loading: The Edit page typically retrieves the record to be edited from the database based on the ID passed in the URL. This is often done in the @code block’s OnInitializedAsync method.

  • [SupplyParameterFromQuery] Attribute: The [SupplyParameterFromQuery] attribute can be used to get parameter values from the query string of the URL. In the context of CRUD pages generated by scaffolding, it is more common to use [SupplyParameterFromRoute] to get the ID from the route parameters. However, the transcript mentions [SupplyParameterFromQuery], which might be applicable if the ID was passed in the query string instead of route parameters. In typical Blazor routing for Edit pages, route parameters are generally used.

    [SupplyParameterFromQuery] Attribute: A Blazor attribute used to bind a component parameter to a value from the query string of the current URL. For example, if the URL is /page?id=123, you can use [SupplyParameterFromQuery] public int Id { get; set; } to access the value 123.

    Query String: The part of a URL that follows the question mark (?). It’s used to pass data to the server in the form of key-value pairs (e.g., ?param1=value1&param2=value2).

    [SupplyParameterFromRoute] Attribute: A Blazor attribute used to bind a component parameter to a value from the route parameters of the current URL. For example, if the route is /items/{id:int}, and the URL is /items/42, you can use [SupplyParameterFromRoute] public int Id { get; set; } to access the value 42.

  • Data Binding and Form Fields: Input components are used to display and edit the properties of the loaded record, with two-way data binding using @bind-Value.

  • UpdateStudent Method: The OnValidSubmit attribute of the EditForm is set to a method (e.g., UpdateStudent) that handles saving the changes to the database. This method typically updates the record in the DB context, saves changes, and navigates back to the Index page.

8.2.4 Delete Page (Delete.razor)

  • Route: Accessed via the “Delete” link from the Index page, typically including the record’s ID in the URL (e.g., /students/delete/{id:int}).
  • Functionality: Provides a confirmation page to delete a record.
  • Confirmation Message: Displays a message asking for confirmation before deletion.
  • EditForm Component: Uses an EditForm component to handle the delete confirmation and action.
  • Data Loading and Display: Similar to the Edit page, the Delete page loads the record to be deleted based on the ID from the URL and displays its details.
  • DeleteStudent Method: The OnValidSubmit attribute of the EditForm is set to a method (e.g., DeleteStudent) that handles the deletion process. This method typically removes the record from the DB context, saves changes, and navigates back to the Index page.

8.2.5 Details Page (Details.razor)

  • Route: Accessed via the “Details” link from the Index page, typically including the record’s ID in the URL (e.g., /students/details/{id:int}).
  • Functionality: Displays read-only details of a single record.
  • Data Loading and Display: Loads the record from the database based on the ID from the URL and displays its properties in a read-only format.

8.3 Enhancing Validation: Interactive Validation

To enable real-time validation (validation as soon as you click out of an input field), you need to make your component page interactive.

  • @rendermode InteractiveServer Directive: Add the @rendermode InteractiveServer directive at the top of your Razor component page to enable interactive server rendering. This will enable client-side validation using Blazor’s interactive features.

Conclusion

This chapter has provided a comprehensive introduction to Blazor, covering its fundamental concepts, project structure, components, event handling, data binding, render modes, and CRUD operations. By understanding these core principles, you are well-equipped to start building your own interactive and data-driven web applications with Blazor. For further practice, consider exploring the suggested “food menu web app project” mentioned at the end of the transcript to reinforce your newly acquired knowledge.