在 ASP.NET Core 2.x 中手动创建 HttpContext

Question

我正在尝试将 Razor 视图呈现为来自托管服务的字符串。通过使用 IRazorViewEngine 我可以使用类似以下的内容将视图呈现为字符串：

 _viewEngine.FindView(actionContext, viewName, false);
var viewDictionary = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
                {
                    Model = model
                };

                var viewContext = new ViewContext(
                    actionContext,
                    viewResult.View,
                    viewDictionary,
                    new TempDataDictionary(actionContext.HttpContext, _tempDataProvider),
                    sw,
                    new HtmlHelperOptions()
                );
                viewContext.RouteData = httpContext.GetRouteData();   //set route data here

                await viewResult.View.RenderAsync(viewContext);

然而，由于缺少 HttpContext 而未从 Controller 中调用它时，它就会分崩离析。我已经尝试手动构建 HttpContext，但是我在 Microsoft Mvc 代码深处遇到了很多错误和空异常，这非常难以调试。我试过像 RazorLight which don't suit my needs because it doesn't properly support the @inject directive. I think my best solution is to try and mock up a fake HttpContext/ControllerContext to pass to the native ViewEngine. However, when I create a new DefaultHttpContext, I get a NullReferenceException around here 这样的库，但是很难跟踪代码并找到它的来源。

有没有办法创建一个新的HttpContext？

Answer 1

试试这个：

public class YourClass 
{
   private readonly IHttpContextAccessor _httpContextAccessor;
   public YourClass(IHttpContextAccessor httpContextAccessor)
   {
      _httpContextAccessor = httpContextAccessor;
   }

   public void YourMethod()
   {
      // access HttpContext with __httpContextAccessor.HttpContext
   }
}

然后在Startupclass中注册IHttpContextAccessor如下：

public void ConfigureServices(IServiceCollection services)
{
    services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();

    // Or you can also register as follows

    services.AddHttpContextAccessor();
}

Answer 2

您可以通过创建一个 DefaultHttpContext 来模拟它，但是 MVC 需要一些在根 DI 范围中不存在的范围内的服务，因此您必须为您的渲染创建一个 ServiceProvider 范围。

这是一个呈现视图的示例 IHostedService（我在 WebApplication 模板中用 MVC 做了运行）：

public class ViewRenderService : IHostedService
{
    private readonly IRazorViewEngine _razorViewEngine;
    private readonly ITempDataProvider _tempDataProvider;
    private readonly IServiceProvider _serviceProvider;

    public ViewRenderService(IRazorViewEngine razorViewEngine,
        ITempDataProvider tempDataProvider,
        IServiceProvider serviceProvider)
    {
        _razorViewEngine = razorViewEngine;
        _tempDataProvider = tempDataProvider;
        _serviceProvider = serviceProvider;
    }

    public async Task<string> RenderToStringAsync(string viewName, object model)
    {
        using (var requestServices = _serviceProvider.CreateScope())
        {
            var httpContext = new DefaultHttpContext { RequestServices = requestServices.ServiceProvider };
            var routeData = new RouteData();
            routeData.Values.Add("controller", "Home");
            var actionContext = new ActionContext(httpContext, routeData, new ActionDescriptor());

            using (var sw = new StringWriter())
            {
                var viewResult = _razorViewEngine.FindView(actionContext, viewName, false);

                if (viewResult.View == null)
                {
                    throw new ArgumentNullException($"{viewName} does not match any available view");
                }

                var viewDictionary = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
                {
                    Model = model
                };

                var viewContext = new ViewContext(
                    actionContext,
                    viewResult.View,
                    viewDictionary,
                    new TempDataDictionary(actionContext.HttpContext, _tempDataProvider),
                    sw,
                    new HtmlHelperOptions()
                );

                await viewResult.View.RenderAsync(viewContext);
                return sw.ToString();
            }
        }
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        var html = await RenderToStringAsync("About", null);
        return;
    }

    public async Task StopAsync(CancellationToken cancellationToken)
    {
    }
}

注意：此示例基于此处找到的博客 post，但经过修改后可在 IHostedService 中使用。 https://ppolyzos.com/2016/09/09/asp-net-core-render-view-to-string/

在 ASP.NET Core 2.x 中手动创建 HttpContext

Manually creating an HttpContext in ASP.NET Core 2.x

c#

httpcontext

asp.net-core-mvc

asp.net-core