Custom tag helper not working

Question

I followed a few guides on creating a custom tag helper for ASP Core.

This is my helper:

using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.Asp         


        

Answer 1

I had the same problem, but it was the result of a rogue, accidental semi-colon at the end of the @addTagHelper line.

I had:

@addTagHelper *, ToolConstrolSystem;

Instead of:

@addTagHelper *, ToolConstrolSystem

While the solution will build and run fine, the tag helper will not work if the @addTagHelper line contains a semi-colon.

Answer 2

Another thing to check if you're finding you can't set your content with calls like:

output.Content.AppendHtml("<tags...>");
output.Content.SetHtmlContent("<tags...>");

Is to check that you didn't use your tag helper as an empty/void element, e.g.:

<my-tag-helper attr="value" />

To add content the tag helper must have a closing tag:

<my-tag-helper attr="value"></my-tag-helper>