ComponentTagHelper

ComponentTagHelper.cs

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;

namespace SampleTagHelpers
{
    [HtmlTargetElement("component")]
    public class ComponentTagHelper : TagHelper
    {
        private readonly IHtmlHelper _htmlHelper;

        public ComponentTagHelper(IHtmlHelper htmlHelper)
        {
            _htmlHelper = htmlHelper;
        }

        public Type Type { get; set; }

        public RenderMode RenderMode { get; set; }

        public object Parameters { get; set; }

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

        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
        {
            // TODO: Validate argument values, e.g. Type should be IComponent

            ((IViewContextAware)_htmlHelper).Contextualize(ViewContext);

            // There should probably be a non-generic overload of IHtmlHelper.RenderComponentAsync which would make the need for
            // the following reflection malarky go away.
            var renderHelper = typeof(HtmlHelperComponentExtensions)
                                    .GetMethod(name: nameof(HtmlHelperComponentExtensions.RenderComponentAsync),
                                                genericParameterCount: 1,
                                                types: new[] { typeof(IHtmlHelper), typeof(RenderMode), typeof(object) });
            
            var renderDelegate = renderHelper.MakeGenericMethod(Type)
                                                .CreateDelegate(typeof(Func<IHtmlHelper, RenderMode, object, Task<IHtmlContent>>));

            var renderAsyncThunk = (Func<IHtmlHelper, RenderMode, object, Task<IHtmlContent>>)renderDelegate;

            output.Content.SetHtmlContent(await renderAsyncThunk(_htmlHelper, RenderMode, Parameters));

            output.TagName = null;
        }
    }
}