Asp.Net Core render ViewComponent to variable

The Reasons

1. NullView is an internal class now. But that's a very simple class that does nothing. In other words, simply copy & paste it from the src into your source code.

2. The tutorials you linked above is used to render a plain view. However, since you're trying to render a view component instead of a view, you should avoid passing a view path directly. You should pass a ViewComponent Class Name (or Type) instead.

   Model = await _viewRender.RenderToStringAsync(
       "/Components/Test/Default.cshtml", // don't pass a view path since we're not rendering a view file but a view component
       "Test",                            // because the `ViewComponent` Name is Test
       new TestModel { StrToPrint = "Print From Service" });
   

3. According to the official docs, The runtime searches for the view in the following paths:

   1. /Views/{Controller Name}/Components/{View Component Name}/{View Name}
   2. /Views/Shared/Components/{View Component Name}/{View Name}
   3. /Pages/Shared/Components/{View Component Name}/{View Name}

   However, your Test ViewComponent resides in Pages/Components/Test/Default.cshtml, which can not be found by Razor by default. Either configure a custom View Location, or move it to the standard location such that Razor can find the view files.

4. Finally, rendering a ViewComponent as a page seems a bit of overkill. I would suggest you should use IViewComponentHelper to render the ViewComponent as an IHtmlContent such that I can write to a StringWriter:

   public class MyViewComponentContext 
   {
       public HttpContext HttpContext { get; set; }
       public ActionContext ActionContext { get; set; }
       public ViewDataDictionary ViewData { get; set; }
       public ITempDataDictionary TempData { get; set; }
   }
   private async Task<string> Render( MyViewComponentContext myViewComponentContext,string viewComponentName,object args) {
       using (var writer = new StringWriter())
       { 
           var helper = this.GetViewComponentHelper(myViewComponentContext, writer);
           var result = await helper.InvokeAsync(viewComponentName, args);  // get an IHtmlContent
           result.WriteTo(writer, HtmlEncoder.Default);
           await writer.FlushAsync();
           return writer.ToString();
       }
   }
   

Demo

If I fix the issues as I described above, when running your project I'll get the correct result: