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Custom Tag Helpers

1. Description​

Custom Tag Helpers let you create reusable, HTML-like components that run server-side code to render HTML. They are classes that inherit from TagHelper and are used in Razor views via custom element/attribute names.

2. Why It Is Important​

They encapsulate repeated rendering logic, improve view readability, and integrate with Tag Helper pipeline (attributes, context, child content).

3. Real-World Examples​

  • A PagerTagHelper to render pagination controls.
  • A BadgeTagHelper to render styled status badges (e.g., <span badge status="active">Active</span>).

4. Syntax & Explanation​

Example: a simple BadgeTagHelper that outputs a colored span.

BadgeTagHelper.cs:

using Microsoft.AspNetCore.Razor.TagHelpers;

[HtmlTargetElement("badge")]
public class BadgeTagHelper : TagHelper
{
    public string Status { get; set; } // attribute: status

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        output.TagName = "span";
        var css = Status == "active" ? "badge badge-success" : "badge badge-secondary";
        output.Attributes.SetAttribute("class", css);
    }
}

Usage in .cshtml:

<badge status="active">Active</badge>

Registration: Tag Helpers are discovered automatically if the assembly is referenced; ensure _ViewImports.cshtml has @addTagHelper *, YourAssemblyName (usually available by default in ASP.NET Core projects).

5. Use Cases​

  • Encapsulate UI widgets (tables, pagers, badges).
  • Keep view markup consistent and DRY.
  • Provide attribute-driven components for designers and developers.

6. Mini Practice Task​

  1. Implement a PagerTagHelper that accepts Page, TotalPages attributes and renders previous/next links.
  2. Create a btn tag helper that renders a bootstrap-styled button with asp-action support.