reading-notes

# View components in ASP.NET Core

view components in ASP.NET Core are powerful, reusable rendering components that offer separation of concerns and testability benefits similar to controllers and views. They are ideal for handling complex rendering logic, such as dynamic navigation menus, sign-in panels, or shopping carts.

To create a view component, you need to define a class derived from ViewComponent or decorated with the [ViewComponent] attribute. The class should include an InvokeAsync method that returns Task or a synchronous Invoke method that returns IViewComponentResult. These methods receive parameters directly from their invocation and not through model binding.

View components are typically invoked within views using the @await Component.InvokeAsync syntax, passing any required parameters. Alternatively, you can invoke a view component as a Tag Helper, specifying the component and its parameters in kebab case.

Lastly, while view components are commonly used within views, they can also be invoked directly from a controller by returning a ViewComponentResult from a controller action. This flexibility allows you to use view components wherever you need reusable rendering logic in your ASP.NET Core application. View Components in ASP.NET Core MVC provide a powerful way to create reusable, self-contained components with their own logic and views. Here’s a summary of key points:

View components are introduced in ASP.NET Core MVC 6 as a replacement for child actions and partial views. They offer separation of concerns and testability, making them ideal for complex rendering tasks.

Creating a Simple View Component:

View components can be created by inheriting from the ViewComponent class, decorating a class with the [ViewComponent] attribute, or naming a class with the “ViewComponent” suffix. They must be public, non-nested, and non-abstract classes. View components include an Invoke method that returns an IViewComponentResult to be rendered.

Rendering a View Component:

View components can be rendered in Razor views using the @Component.Invoke helper method. It’s recommended to use nameof(Navigation) instead of hardcoded strings to reference view components. The @using directive in _ViewImports.cshtml is used to import the namespace of the view component.

Returning Views from View Components:

View components can return views using the View helper method. The convention for locating views is in the Views/Shared/Components/{ComponentName}/Default.cshtml or Views/{ControllerName}/Components/{ComponentName}/Default.cshtml paths. Views can be named explicitly by passing a view name as a string to the View method.

Using View Models:

View components can use view models to encapsulate data. View models can be defined as nested classes within the view component class. Data can be passed to views through view models.

Asynchronous View Components:

View components can be asynchronous by implementing the InvokeAsync method and returning a Task. This is useful for performing asynchronous operations within view components.

Dependency Injection in View Components:

ASP.NET Core’s built-in dependency injection allows you to inject services into view components via constructor injection. You can use injected services to make decisions and customize the behavior of your view components. Overall, view components in ASP.NET Core MVC provide a flexible and powerful way to encapsulate rendering logic and create reusable components that can be easily integrated into your web application.