Advanced ASP.NET Core MVC: Mastering View Components

Welcome to this in-depth tutorial on View Components in ASP.NET Core MVC. View Components are powerful tools for encapsulating reusable UI logic, making your applications cleaner, more modular, and easier to maintain.

What are View Components?

View Components are similar to partial views, but they are designed for more complex scenarios. They consist of a class (like a controller) and a view (like a partial view). They are ideal for:

• Displaying dynamic data.
• Implementing reusable UI elements that don't require a full controller action.
• Separating concerns for complex UI sections.

Creating a Basic View Component

Let's start by creating a simple View Component that displays a list of categories.

1. The View Component Class

Create a new class, for example, CategoryList.cs, in a ViewComponents folder in your project.

public class CategoryList : ViewComponent
{
    public IViewComponentResult Invoke()
    {
        // In a real application, you would fetch this data from a database or service.
        var categories = new List<string> { "Electronics", "Books", "Clothing", "Home Goods" };
        return View(categories);
    }
}

2. The View Component's View

Create a corresponding Razor view. The convention is to place it in Views/Shared/Components/CategoryList/Default.cshtml.

@model IEnumerable<string>

<div class="category-widget">
    <h4>Categories</h4>
    <ul>
        @foreach (var category in Model)
        {
            <li><a href="#">@category</a></li>
        }
    </ul>
</div>

// Optional: You can also specify a different view name if needed.

3. Invoking the View Component in a View

In your regular Razor view (e.g., Views/Home/Index.cshtml), you can invoke the View Component using the <vc:category-list></vc:category-list> tag helper.

@{
    ViewData["Title"] = "Home Page";
}

<div class="text-center">
    <h1 class="display-4">Welcome</h1>
    <p>Learn about View Components in ASP.NET Core.</p>

    <!-- Invoking the View Component -->
    <vc:category-list></vc:category-list>
</div>

Advanced Features

Handling Parameters

View Components can accept parameters to customize their behavior. The Invoke method overload is used for this.

Example: View Component with a Maximum Count Parameter

public class CategoryListWithCount : ViewComponent
{
    public IViewComponentResult Invoke(int maxCount)
    {
        // Fetch data, applying the maxCount filter
        var categories = new List<string> { "Electronics", "Books", "Clothing", "Home Goods", "Toys", "Groceries" }
            .Take(maxCount)
            .ToList();

        return View(categories);
    }
}

Invoke in the view:

<vc:category-list-with-count max-count="3"></vc:category-list-with-count>

Named Views

If you need to return different views based on certain conditions, you can use named views.

public IViewComponentResult Invoke()
{
    var hasData = true; // Example condition
    if (hasData)
    {
        return View("Default", new[] { "Data1", "Data2" });
    }
    else
    {
        return View("Empty");
    }
}

You would then create Empty.cshtml in the same component folder.

View Component Selectors

You can use the [ViewComponent(Name = "CustomName")] attribute to specify a different name for your View Component.

Best Practices

• Keep View Components focused on a single, reusable UI element.
• Avoid complex logic within View Components; delegate to services.
• Use dependency injection to resolve services within your View Component.
• Test your View Components thoroughly.