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Custom Tag Helper in ASP.NET Core

In the last tutorial we covered Built-In Tag Helpers in ASP.NET Core. Now we will learn to create Custom Tag Helper for transforming the html elements with C# codes. We will take a lot of examples so make sure to go through each of the sections on this tutorial.

This tutorial is a part of the series called Tag Helpers in ASP.NET Core. It contains 3 tutorials.

• 1. Introduction to Tag Helpers in ASP.NET Core
• 2. Built-In Tag Helpers in ASP.NET Core
• 3. Custom Tag Helper in ASP.NET Core

Built-In Tag Helpers in ASP.NET Core

Many of the ASP.NET Core Tag Helpers comes pre-built in the framework and are represented as asp-* attributes. They perform tasks like enhancing forms, validation messages, designing layouts and so on. In this section I am going to discuss about the built in Tag Helpers for Form, Input, Select, Label, Anchor, Text Area elements, CSS, JS and Cache.

This tutorial is a part of the series called Tag Helpers in ASP.NET Core. It contains 3 tutorials.

• 1. Introduction to Tag Helpers in ASP.NET Core
• 2. Built-In Tag Helpers in ASP.NET Core
• 3. Custom Tag Helper in ASP.NET Core

Introduction to Tag Helpers in ASP.NET Core

What are Tag Helpers in ASP.NET Core ? Tag Helpers are reusable components in ASP.NET Core. They are used to perform "defined transformations on HTML elements" from C# codes before being rendered on the views. With Tag Helpers we can enable server-side code to participate in creating and rendering the HTML elements. The most commonly used tag helpers are asp-controller and asp-action which assigns the controller & action for generating the URL. Example: <a asp-controller="Shop" asp-action="Clothes">Buy Clothes</a> will generate HTML <a href"/Shop/Clothes">Buy Clothes</a>.

How to Call Web API in ASP.NET Core [.NET 7.0]

On my previous tutorial called How to Create Web APIs in ASP.NET Core [RESTful pattern] I created a Web API. Now I will call this API (i.e. consume the API) in another project known as client.

How to Create Web APIs in ASP.NET Core [.NET 7.0 RESTful pattern]

Creating Web APIs in ASP.NET Core is very straightforward. You create controllers that have 3 things:

• 1. They should have [ApiController] attribute on them. This attribute tells that the controller will server HTTP API Responses.
• 2. They should derive from ControllerBase class instead of Controller class.
• 3. They should have attribute routing applied on them like [Route("someUrl/[controller]")].

The controller of a Web API looks like:

Areas and Routing in ASP.NET Core

ASP.NET Core Areas represent a functional segment of the application. It can be administration, billing, sales, etc. If our application becomes very large then it will have many controllers, Models & Views. We can create multiple Areas to distribute the application files into them. This will help us to manage our application in a better way.

ASP.NET Core Routing Generating URLs

ASP.NET Core Attribute Routing

ASP.NET Core Attribute Routing adds routes by applying C# attributes on the controller and actions methods. Note that if convention routes are also present then we can override them by adding attribute routes. This is because DOT NET gives preference to attribute routes.

Learn ASP.NET Core Route Constraint in details with lots of examples

ASP.NET Core Routing Constraints restricts route matching to a set of URLs. This is done by applying different types of constraints or rules in the route patterns.

Let’s start understanding this topic by creating a simple example project.

Learn ASP.NET Core Convention-Based Routing

What is ASP.NET Core routing? Routing is used to create URL patterns for a web app. These route patterns match the incoming HTTP requests and dispatches these requests to the endpoints in the app. Endpoints are those units that are responsible for handling these requests. Most commonly endpoints are the Controllers in an ASP.NET Core MVC app.

In the Program.cs class we can define one or more ASP.NET Core Routes to perform the following tasks: