View Components are self-contained, reusable UI building blocks in ASP.NET Core MVC. They are designed to encapsulate rendering logic that’s more complex than what you’d typically put in a partial view but doesn’t warrant the complexity of a full controller and view.
Best Practices Naming: View Component classes should end with the suffix ViewComponent (e.g., ProductListViewComponent). Structure: Place View Components in the ViewComponents folder. The associated view file should be placed in Views/Shared/Components/{ViewComponent Name}/{View Name}.cshtml. Data: Pass data to the View Component using a strongly typed model or view model. Asynchronous: Use asynchronous methods (InvokeAsync) to avoid blocking threads when performing data access or other I/O operations. Simplicity: Keep the View Component’s logic focused on rendering the UI element. Avoid complex business logic within the component.
Things to Avoid Overuse: Don’t use View Components for simple UI elements that can be handled by partial views. Tight Coupling: Avoid tightly coupling View Components to specific controllers or actions. Make them reusable across different parts of your application. Complex Logic: View Components should not be responsible for handling business logic. Instead, delegate that to your models or services. Direct Database Access: Avoid directly accessing your database from within a View Component. Use services for data access.
When to Use View Components Complex UI Elements: When a UI element requires more complex rendering logic than a simple partial view. Data-Driven Elements: When you need to fetch data or perform some computation before rendering the UI element. Reusable Widgets: When you want to create a reusable widget that can be used in different parts of your application.
Implement View Components Create a View Component Class: Derive from ViewComponent and implement an Invoke or InvokeAsync method. Create a View: Create a Razor view file (.cshtml) within the Views/Shared/Components/{ViewComponent Name} folder. Invoke in Your View: Use the @await Component.InvokeAsync(“ViewComponent Name”, arguments) helper in your main view to render the View Component.
Code // GridViewComponent.cs (View Component) public class GridViewComponent : ViewComponent { public async Task<IViewComponentResult> InvokeAsync() { // Data for the view component (could come from a database, service, etc.) PersonGridModel model = new PersonGridModel() { GridTitle = “Persons List”, Persons = new List<Person>() { new Person() { PersonName = “John”, JobTitle = “Manager” }, // more people } };
// ViewBag is not ideal; prefer using a strongly typed model ViewData[“Grid”] = model;
return View(“Sample”); // This will look for the view in Views/Shared/Components/Grid/Sample.cshtml } }
<vc:grid></vc:grid> // alternative syntax (not preferred, as it is not strongly typed)
Explanation: The GridViewComponent class is a view component that fetches a list of people and passes it to the “Sample” partial view along with a grid title using ViewBag. Views/Home/Index.cshtml and Views/Home/About.cshtml invoke the Grid view component using @await Component.InvokeAsync(“Grid”) (or, less ideally, the vc:grid tag helper), rendering the person list in a grid format.
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Partial Views in Asp.net Core MVC