如何从自定义中间件返回视图？答案

【问题标题】：how to return view from custom middleware?如何从自定义中间件返回视图？
【发布时间】：2022-08-16 18:10:00
【问题描述】：

我的目标是使用中间件拦截 404 状态代码并返回自定义视图（中断执行）。

我尝试了一些例子。而且，只有await context.Response.WriteAsync(\"test 404 response error\"); 有效。但这不是我需要的。

如何做到这一点？

我的下一个示例不起作用（我的意思是我得到了空白页面或默认的 Chrome 未找到页面）：

public class CustomError404Middleware
{
    private readonly RequestDelegate _next;

    public CustomError404Middleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        await _next(context);

        if (context.Response.StatusCode == 404 && !context.Response.HasStarted)
        {
            //Re-execute the request so the user gets the error page
            var originalPath = context.Request.Path.Value;
            context.Items[nameof(Defaults.ORIGINAL_PATH)] = originalPath;
            context.Request.Path = \"Error/404\";
            // context.Request.Path = \"/Error/404\";

            await _next(context);
        }
    }
}

配置：

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseMigrationsEndPoint();
            }
            else
            {
                app.UseExceptionHandler(\"/Home/Error\");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            // app.UseStatusCodePages();

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseRouting();
            app.UseAuthentication();
            app.UseAuthorization();

            app.UseMiddleware<RequestLoggerMiddleware>();
            app.UseMiddleware<CustomError404Middleware>();

.............. skipped (Rollbar, CORS) ..............

            app.UseSession();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: \"dashboard\",
                    pattern: \"{controller=Home}/{action=Index}\");
                endpoints.MapRazorPages();
                endpoints.MapMetrics();
            });

控制器和视图：

    [AllowAnonymous]
    public class ErrorController : Controller
    {
        [ActionName(\"404\")]
        public IActionResult PageNotFound()
        {
            ViewData[nameof(Defaults.ORIGINAL_PATH)] = \"unknown\";

            if (HttpContext.Items.ContainsKey(nameof(Defaults.ORIGINAL_PATH)))
            {
                ViewData[nameof(Defaults.ORIGINAL_PATH)] = HttpContext.Items[Defaults.ORIGINAL_PATH] as string;
            }

            return View();
        }
    }

@ViewData[nameof(Defaults.ORIGINAL_PATH)]

<div>
    <p>
        test
    </p>
</div>

标签： middleware .net-5 404-page

【解决方案1】：

为了达到类似的目的，我在中间件类中创建了一个辅助方法

private Task GetViewResultTask(HttpContext context, string viewName)
{
    var viewResult = new ViewResult()
    {
        ViewName = viewName
    };

    var executor = context.RequestServices.GetRequiredService<IActionResultExecutor<ViewResult>>();
    var routeData = context.GetRouteData() ?? new Microsoft.AspNetCore.Routing.RouteData();
    var actionContext = new ActionContext(context, routeData,
    new Microsoft.AspNetCore.Mvc.Abstractions.ActionDescriptor());
    return executor.ExecuteAsync(actionContext, viewResult);
}

然后从我真正想要返回视图的中间件（可能在一些条件逻辑之后，或者做一些其他事情之后），我会

await GetViewResultTask(context, "~/Views/Home/NotRegistered.cshtml");
return;

【讨论】：

你好。这是某种死灵张贴:) 但照原样......我无法通过您提供的解决方案取得成功。解决方案有问题，或者我没有足够的经验。所以，我用“重新执行”做到了谢谢。

【解决方案2】：

最后，经过所有尝试，我使用内置的“重新执行”解决了问题

//startup.cs
app.UseStatusCodePagesWithReExecute("/Error/{0}");

控制器和视图：

//controller
[HttpGet]
[ActionName("404")]
public async Task<IActionResult> Error404()
{
    return await Task.Run(() => View(ErrorModel(HttpContext)));
}

private ErrorViewModel ErrorModel(HttpContext context)
{
    return new ErrorViewModel(OriginalUrl(context), RequestId(context));
}

private string OriginalUrl(HttpContext context)
{
    var feature = HttpContext.Features.Get<IStatusCodeReExecuteFeature>();

    return feature?.OriginalPath;
}

private string RequestId(HttpContext context)
{
   return Activity.Current?.Id ?? context.TraceIdentifier;
}

//view just as a sample
<div class="h-100 mt-4">
    <div class="d-flex justify-content-center align-items-center h-100">
        <div class="text-center">
            <p class="font-weight-bold" style="font-size:10rem">404</p>
            <br />
            <p class="font-weight-bold" style="font-size:3rem">Requested page not found</p>
            <br />
            <p class="font-weight-bold">ID: @Model.RequestId</p>
            <p class="font-weight-bold">URL: @Model.OriginalUrl</p>
        </div>
     </div>
 </div>

【讨论】：