How to Render Views as Strings in ASP.NET Core?

Rendering Views as Strings in .NET Core

In ASP.NET Core, rendering views as strings is a crucial capability often required for scenarios like reporting, dynamic content generation, or testing. This article will guide you through the process of achieving this in .NET Core, addressing the specific issue faced while converting existing code from ASP.NET to .NET Core.

Using Controller Extensions for View Rendering

To render views as strings in .NET Core, an effective approach is to create a controller extension method. This method provides a convenient way to access and render views from any controller within your application. Here's an example implementation:

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using System.IO;
using System.Threading.Tasks;

namespace CoreApp.Helpers
{
    public static class ControllerExtensions
    {
        public static async Task<string> RenderViewAsync<TModel>(this Controller controller, string viewName, TModel model, bool partial = false)
        {
            // Handle missing view name
            if (string.IsNullOrEmpty(viewName))
            {
                viewName = controller.ControllerContext.ActionDescriptor.ActionName;
            }

            // Set the view data
            controller.ViewData.Model = model;

            using (var writer = new StringWriter())
            {
                // Obtain the view engine
                IViewEngine viewEngine = controller.HttpContext.RequestServices.GetService(typeof(ICompositeViewEngine)) as ICompositeViewEngine;

                // Find the view
                ViewEngineResult viewResult = viewEngine.FindView(controller.ControllerContext, viewName, !partial);

                // View not found
                if (viewResult.Success == false)
                {
                    return $"A view with the name {viewName} could not be found";
                }

                // Render the view
                ViewContext viewContext = new ViewContext(
                    controller.ControllerContext,
                    viewResult.View,
                    controller.ViewData,
                    controller.TempData,
                    writer,
                    new HtmlHelperOptions()
                );

                await viewResult.View.RenderAsync(viewContext);

                // Return the rendered view as a string
                return writer.GetStringBuilder().ToString();
            }
        }
    }
}

Using the Extension Method

To use the extension method, simply add the following code to your controller:

var viewHtml = await this.RenderViewAsync("Report", model);

For rendering a partial view:

var partialViewHtml = await this.RenderViewAsync("Report", model, true);

Enhancements Over the Original Code

The provided extension method includes several enhancements over the original code:

• Strong-typing for the model
• Error checking for view not found
• Ability to render both views and partial views
• Asynchronous execution
• No dependency injection or additional services required

By utilizing this approach, you can easily render and access views as strings in .NET Core, providing flexibility for various scenarios where dynamic content generation is necessary.

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