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ASP.NET Core MVC中，如何将视图文件生成的html代码通过字符串返回

下面的方法可以在ASP.NET Core MVC中，将视图文件生成的html代码通过字符串返回。

首先定义一个静态类ControllerExtensions，里面包含Controller的扩展方法RenderViewAsync，用于返回视图文件生成的html代码：

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 AspNetCore3000ViewGenerator.Models
{
    public static class ControllerExtensions
    {
        public static async Task<string> RenderViewAsync(this Controller controller, string viewName, object model, bool partial = false)
        {
            if (string.IsNullOrEmpty(viewName))
            {
                viewName = controller.ControllerContext.ActionDescriptor.ActionName;
            }

            controller.ViewData.Model = model;

            using (var writer = new StringWriter())
            {
                IViewEngine viewEngine = controller.HttpContext.RequestServices.GetService(typeof(ICompositeViewEngine)) as ICompositeViewEngine;
                ViewEngineResult viewResult = viewEngine.FindView(controller.ControllerContext, viewName, !partial);

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

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

                await viewResult.View.RenderAsync(viewContext);

                return writer.GetStringBuilder().ToString();
            }
        }
    }
}

然后可以在ASP.NET Core MVC的Controller中调用RenderViewAsync方法，返回一个视图文件生成的html代码：

using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using AspNetCore3000ViewGenerator.Models;

namespace AspNetCore3000ViewGenerator.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;

        public HomeController(ILogger<HomeController> logger)
        {
            _logger = logger;
        }

        public async Task<IActionResult> Index()
        {
            this.ViewData["Message"] = "This is a demo message!";//在Controller中设置ViewData的值后，就可以在下面调用RenderViewAsync方法生成视图Index.cshtml的html代码时，在视图Index.cshtml中获取到ViewData的值
            string html = await this.RenderViewAsync("Index", null);//获取HomeController下，通过视图Index.cshtml生成的html代码

            return View();
        }
    }
}

视图Index.cshtml的代码如下：

@{
    Layout = null;
}

<!DOCTYPE html>

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
</head>
<body>
    <div>
        <h1>Index view!</h1>
    </div>
    <div>
        @ViewData["Message"].ToString()<!--在视图Index.cshtml中，获取ViewData的值-->
    </div>
</body>
</html>