Aspnetcore.docs: Author asp-route-mycustomvalue="true" like helpers?

[weitzhandler]

Hi,

I came looking on how to author a TagHelper that applies on the helper name itself.
For example asp-attribute-if-class="@condition".

Can you please include information about this in the documentation or link it?

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Document Details

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• ID: 19ecfbee-8b84-9ef2-65b6-8c2542f6370f
• Version Independent ID: 9a0cbaa2-65c9-1618-1003-5fd2e7f6192f
• Content: Author Tag Helpers in ASP.NET Core
• Content Source: aspnetcore/mvc/views/tag-helpers/authoring.md
• Product: aspnet-core
• Technology: aspnetcore-mvc
• GitHub Login: @Rick-Anderson
• Microsoft Alias: riande

[serpent5]

I think I can help with this. @weitzhandler Can you provide a more specific example of what it is you’re looking to achieve?

[weitzhandler]

@serpent5 thanks for your good intention!

I've already found the solution, but what I meant is how to author a tag-helper that reads anything after the tag, plus the assigned value.

For instance:

<input asp-class-if-active="@item.IsActive"/>

Will generate the element and add the active class if the condition is true, otherwise, that class won't be generated.

<input class="active"/>

Here's the code:

```c#
[HtmlTargetElement("", Attributes = ClassPrefix + "")]
public class IfAttributeClassTagHelper : TagHelper
{
private const string ClassPrefix = "asp-if-class-";

    [HtmlAttributeName("class")]
    public string CssClass { get; set; }

    IDictionary<string, bool> _ClassValues;

    [HtmlAttributeName("", DictionaryAttributePrefix = ClassPrefix)]
    public IDictionary<string, bool> ClassValues
    {
        get
        {
            return _ClassValues ?? (_ClassValues =
                new Dictionary<string, bool>(StringComparer.OrdinalIgnoreCase));
        }
        set { _ClassValues = value; }
    }

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        var items = ClassValues.Where(e => e.Value).Select(e => e.Key).ToList();

        if (!string.IsNullOrEmpty(CssClass))
            items.Insert(0, CssClass);

        if (items.Any())
        {
            var classes = string.Join(" ", items);
            output.Attributes.Add("class", classes);
        }
    }
}

```

Would be nice if the HtmlAttributeName and it's underlying functionality would have been documented.

Thanks a load again!

[gbjbaanb]

So true, all the built-in taghelpers have asp-XYZ attributes, but the doc doesn't explain how to create our own. This is quite an omission!

[Rick-Anderson]

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