Calling TagHelpers from another TagHelper?

Question

Is there any way to get a TagHelper to render another TagHelper?

Example TagHelpers;

public class OuterTagHelper : TagHelper
{
    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        output.TagName = "";
        output.Content.SetContent("Hello <inner></inner>");
    }
}

public class InnerTagHelper : TagHelper
{
    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        output.TagName = "";
        output.Content.SetContent("World!");
    }
}

Example View;

<outer></outer>

Expected Result;

Hello World!

I know I probably should use a ViewComponent instead, but is it at all possible to achieve the expected behavior presented above?

Answer 1

If you need to use some of the existing tag helper type functionality then you can access it from IHtmlGenerator. This won't help to access custom tag helper functionality but if you just need the functionality of existing stuff like label, input then this will work

[HtmlTargetElement("input", Attributes = nameof(Wrap) + ", asp-for")]
[HtmlTargetElement("select", Attributes = nameof(Wrap) + ", asp-for")]
public class FormGroupWrapperTagHelper : TagHelper
{
    public FormGroupWrapperTagHelper(IHtmlGenerator generator)
    {
        Generator = generator;
    }

    [HtmlAttributeNotBound]
    [ViewContext]
    public ViewContext ViewContext { get; set; }

    protected IHtmlGenerator Generator { get; }

    public ModelExpression AspFor { get; set; }
    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        var generateValidationMessage = Generator.GenerateValidationMessage(ViewContext,
                                                                  AspFor.Name,
                                                                  message: null,
                                                                  tag: null,
                                                                  htmlAttributes: null);
.....
}