Develop Reference

How can to map to a wrapper class using Mapster?

Based on my project I need to create a wrapper for “IFormFile”, Actually I created a “AppFileProxy” class and “IAppFile” interface for this purpose :
IAppFile.cs :
public interface IAppFile
{
string Name { get; }
string FileName { get; }
string ContentType { get; }
long Length { get; }
void CopyTo(Stream target);
Task CopyToAsync(Stream target, CancellationToken cancellationToken = default);
Stream OpenReadStream();
}
AppFileProxy.cs :
public class AppFileProxy : IAppFile
{
private readonly IFormFile _formFile;
public AppFileProxy(IFormFile formFile)
{
_formFile = formFile ?? throw new ArgumentNullException(nameof(formFile));
}
public string Name => _formFile.Name;
public string FileName => _formFile.FileName;
public string ContentType => _formFile.ContentType;
public long Length => _formFile.Length;
public void CopyTo(Stream target)
{
_formFile.CopyTo(target);
}
public Task CopyToAsync(Stream target, CancellationToken cancellationToken = default)
{
return _formFile.CopyToAsync(target, cancellationToken);
}
public Stream OpenReadStream()
{
return _formFile.OpenReadStream();
}
}
Now, I want to Map “IFormFile” to “IAppFile” by using Mapster in the action controller as shown below :
CompanyDto.cs :
public class CompanyDto
{
public string Name { get; set; }
public IFormFile Logo { get; set; }
}
CompanyMapDto.cs :
public class CompanyMapDto : IRegister
{
public int Id { get; set; }
public string Name { get; set; }
public IAppFile Logo { get; set; }
public void Register(TypeAdapterConfig config)
{
config.ForType<CompanyDto, CompanyMapDto>()
.Map(dest => dest.Logo, src => new AppFileProxy(src.Logo));
}
}
action controller :
[HttpPost]
[Route("[controller]/[action]")]
public async Task<IActionResult> AddCompanyWithLogo([FromForm]CompanyDto dto)
{
CompanyMapDto company = dto.Adapt<CompanyMapDto>();
var stream = company.Logo.OpenReadStream();
return Ok();
}
But When I call action I get exception error for OpenReadStream() method :
System.NotImplementedException: The method or operation is not implemented.
at GeneratedType_1.OpenReadStream()
at MapsterInDotNet.Controllers.CompaniesController.AddCompanyWithLogo(CompanyDto dto) in C:\Users\Mohsen\source\repos\UseMapsterInDotNet\MapsterInDotNet\MapsterInDotNet\Controllers\CompaniesController.cs:line 52
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
How do I resolve this?

Well. I managed to make it work. You have to explicitly configurate mapping from IAppFile to IFormFile.
So instead of your configuration:
config.ForType<CompanyDto, CompanyMapDto>()
.Map(dest => dest.Logo, src => new AppFileProxy(src.Logo));
Use this:
TypeAdapterConfig<IFormFile, IAppFile>.ForType() // Or NewConfig()
.MapWith(src => new AppFileProxy(src));

What is the reason for this error? (.Net 5, C#)

I am coding a dynamic website, everything works but I noticed an error in the terminal.
Error:
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: Cannot perform runtime binding on a null reference
at CallSite.Target(Closure , CallSite , Object )
at AspNetCore.Views_Content_CategoryContent.ExecuteAsync() in C:\Users\lenovo\Desktop\Projeler\Wutemp\Views\Content\CategoryContent.cshtml:line 2
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ActionContext actionContext, IView view, ViewDataDictionary viewData, ITempDataDictionary tempData, String contentType, Nullable`1 statusCode)
at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewResultExecutor.ExecuteAsync(ActionContext context, ViewResult result)
at Microsoft.AspNetCore.Mvc.ViewResult.ExecuteResultAsync(ActionContext context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
--- End of stack trace from previous location ---
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()
--- End of stack trace from previous location ---
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
Controller (Edit: I accidentally deleted the ViewBag part):
[Route("Content/{url}/{id}")]
public IActionResult Index(int id)
{
var content = repoContents.TGet(id);
//If content has a category, go to CategoryContent
if(content.ContentCategory != null && content.ContentCategory != 0){
return RedirectToAction("CategoryContent", new
{
category = repoContentCategories.TGet((int)content.ContentCategory).Title,
url = content.URL,
id = content.ID
});
}
else{
ViewBag.Content = content;
return View();
}
}
What is the problem, and how can I solve it?

I solved the problem.
I used model instead of ViewBag mentioned in comments it didn't work I kept getting the same error
I think the problem is due to the similarity of the route parts of the 2 Views.
Index:
[Route("Content/{url}/{id}")]
public IActionResult Index(int id)
{
var content = repoContents.TGet(id);
//If content has a category, go to CategoryContent
if(content.ContentCategory != null && content.ContentCategory != 0){
return RedirectToAction("CategoryContent", new
{
category = repoContentCategories.TGet((int)content.ContentCategory).Title,
url = content.URL,
id = content.ID
});
}
else{
ViewBag.Content = content;
return View();
}
}
CategoryContent:
[Route("Content/{category}/{url}/{id}")]
public IActionResult CategoryContent(int id)
{
ViewBag.Content = repoContents.TGet(id);
return View();
}
I solved the problem by changing the Route part of the ContentCategory page
[Route("Content/{category}/{url}/{id}")]
|
V
[Route("Category-Content/{category}/{url}/{id}")]

Value cannot be null. (Parameter 'value')

I have created a method where a user can log into my application and then a Token is sent to the user so it can be used to view any other views in the application.When i test the login method on postman i get the 500 server error as below instead of the token. I have seen similar questions/posts but haven't seen one that is related to JWT
Below is the output
System.ArgumentNullException: Value cannot be null. (Parameter 'value')
at System.Security.Claims.Claim..ctor(String type, String value, String valueType, String issuer, String originalIssuer, ClaimsIdentity subject, String propertyKey, String propertyValue)
at System.Security.Claims.Claim..ctor(String type, String value)
at Coop_Marketing.Controllers.AccountController.Login(LoginViewModel formdata) in /Users/Ken/Desktop/Coop_Marketing/Coop_Marketing/Coop_Marketing/Controllers/AccountController.cs:line 101
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
at Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
The Account controller with the login method is below
public async Task<IActionResult> Login([FromBody] LoginViewModel formdata)
{
// Get the User from database
var user = await _userManager.FindByNameAsync(formdata.Username);
var roles = await _userManager.GetRolesAsync(user);
var key = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(_appSettings.Secret));
double tokenExpiryTime = Convert.ToDouble(_appSettings.ExpireTime);
if(user !=null && await _userManager.CheckPasswordAsync(user,formdata.Password))
{
var tokenhandler = new JwtSecurityTokenHandler();
// Describe the token used by the user to log in
var tokenDescriptor = new SecurityTokenDescriptor
{
Subject = new ClaimsIdentity(new Claim[]
{
new Claim(JwtRegisteredClaimNames.Sub, formdata.Username),
new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
new Claim(ClaimTypes.NameIdentifier, user.Id),
new Claim(ClaimTypes.Role, roles.FirstOrDefault()),
new Claim("LoggedOn", DateTime.Now.ToString()),
}),
SigningCredentials = new SigningCredentials(key, SecurityAlgorithms.HmacSha256Signature),
Issuer = _appSettings.Site,
Audience = _appSettings.Audience,
Expires = DateTime.UtcNow.AddMinutes(tokenExpiryTime)
};
// Generate the token
var token = tokenhandler.CreateToken(tokenDescriptor);
return Ok(new {token= tokenhandler.WriteToken(token), expiration = token.ValidTo,username = user.UserName,userRole = roles.FirstOrDefault()});
}
// Return error
ModelState.AddModelError("","Username/Password was not Found");
return Unauthorized(new { LoginError = "Please check the Login Credentials - Invalid Username/Password was entered" });
}
}
}
And the LoginViewModel
public class LoginViewModel
{
[Required]
[Display(Name = "User Name")]
public string Username { get; set; }
[Required]
[DataType(DataType.Password)]
public string Password { get; set; }
}
The problem is with > var tokenDescriptor = new SecurityTokenDescriptor as per line 101 in the code which is mentioned in the output. However,I have failed to figure out why I am getting the error.

So it is like Claim has a null parameter. for that, you found this issue.
Update your code like below:-
.....
Subject = new ClaimsIdentity(new Claim[]
{
new Claim(JwtRegisteredClaimNames.NameId,formdata.UserName), //modified
new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
new Claim(JwtRegisteredClaimNames.Sub, user.Id.ToString()), //modified
new Claim(ClaimTypes.Role, roles.FirstOrDefault()),
new Claim("LoggedOn", DateTime.Now.ToString()),
}),
.....
Hope it will resolve your issue.

As you can see in the official documentation, the constructor will throw an argument null exception when the claim type/value is null.
So it seems you are passing a null value(s) to the Claim constructor when creating the Claim object array.
As #Jasen mentioned to make the debugging easier change the one-line Claims array creation just for debugging and put a breakpoint to identify which claim is the culprit.

Polymorphic model binding for generic type parameter

I'm sending a partial object along with a file.
var formData = new FormData();
formData.append('model', JSON.stringify({ ... }));
formData.append('file', file, file.name)
// send formData to backend
My controller method is using Delta<T> from OData.
[HttpPatch("{id}")]
public async Task<IActionResult> Patch(
[FromRoute] Guid id,
[ModelBinder(BinderType = typeof(FormDataJsonBinder))] Delta<AbstractModel> model,
IFormFile file = null
)
However I'm not sending Delta<AbstractModel> as AbstractModel is an abstract class. So I'm really sending Delta<DerivedModel> or Delta<AnotherDerivedModel> etc...
My problem is that ASP.NET keeps throwing saying that it cannot cast to Delta<DerivedModel>
System.InvalidCastException: Unable to cast object of type 'Microsoft.AspNet.OData.Delta`1[DerivedModel]' to type 'Microsoft.AspNet.OData.Delta`1[AbstractModel]'.
at lambda_method308(Closure , Object , Object[] )
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
Here's my FormDataJsonBinder
public class FormDataJsonBinder : IModelBinder
{
public async Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null) throw new ArgumentNullException(nameof(bindingContext));
// Fetch the value of the argument by name and set it to the model state
string fieldName = bindingContext.FieldName;
var valueProviderResult = bindingContext.ValueProvider.GetValue(fieldName);
if (valueProviderResult == ValueProviderResult.None) return Task.CompletedTask;
else bindingContext.ModelState.SetModelValue(fieldName, valueProviderResult);
// Do nothing if the value is null or empty
string value = valueProviderResult.FirstValue;
if (string.IsNullOrEmpty(value)) return Task.CompletedTask;
try
{
// Delta is a special case
if (bindingContext.ModelType.IsAssignableTo(typeof(Delta)))
{
var jsonObject = JObject.Parse(value);
// This extracts type T from Delta<T>
var innerModelType = bindingContext.ModelType.GenericTypeArguments.First();
if (jsonObject["#odata.type"] is not null)
{
var odataType = jsonObject["#odata.type"].Value<string>();
innerModelType = Type.GetType(odataType);
}
var innerModel = JsonConvert.DeserializeObject(value, innerModelType);
var deltaType = typeof(Delta<>).MakeGenericType(innerModelType);
var delta = Activator.CreateInstance(deltaType) as IDelta;
foreach (var property in jsonObject.Properties())
{
delta.TrySetPropertyValue(property.Name, innerModel.GetType().GetProperty(property.Name)?.GetValue(innerModel));
}
bindingContext.Result = ModelBindingResult.Success(delta);
}
else
{
// Deserialize the provided value and set the binding result
var result = JsonConvert.DeserializeObject(value, bindingContext.ModelType);
bindingContext.Result = ModelBindingResult.Success(result);
}
}
catch (JsonException)
{
bindingContext.Result = ModelBindingResult.Failed();
}
return Task.CompletedTask;
}
}
I also tried using a IModelBinderProvider as recommended here, but that also just throws "cannot cast to Delta<DerivedModel>"

The solution was to create the Delta object the right way.
var delta = Activator.CreateInstance(bindingContext.ModelType, innerModelType) as IDelta;

Threading issue when using IViewComponentHelper to convert ViewComponent to HTML string

I'm trying to use IViewComponentHelper in a multi threaded manner. But it's throwing :( (see full exception at bottom of post)
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.AspNetCore.Http.DefaultHttpContext.get_Items()
I have no idea why.
Here's my setup: (simplified for brevity)
Controller:
public async Task<IActionResult> Get()
{
var pdfStream = await _pdfService.GenerateAsync();
return File(pdfStream, "application/pdf");
}
PdfService:
public class PdfService
{
private readonly PdfSDK _pdfSDK;
public constructor(PdfSDK pdfSDK)
{
_pdfSDK = pdfSDK;
}
public async Task<Stream> GenerateAsync()
{
List<Task<PdfDocument>> tasks = await _context.Foos.Select(x => DoWorkAsync(x));
var pdfs = await Task.WhenAll(tasks);
var mergedPdf = _pdfSDK.MergePdfs(pdfs);
return mergedPdf.Stream;
}
private async Task<PdfDocument> DoWorkAsync(Foo foo)
{
var html = await _renderViewComponentService.RenderViewComponentAsStringAsync<MyViewComponent>(foo);
var document = await _pdfSDK.HtmlToDocumentAsync(html);
return document;
}
}
PdfSDK:
public class PdfSDK
{
public async Task<PdfDocument> HtmlToDocumentAsync(string html)
{
using var pdfEngine = new PdfEngine();
var pdf = await pdfEngine.HtmlAsPdfAsync(html);
return pdf;
}
public PdfDocument MergePdfs(params PdfDocument[] pdfs)
{
var pdf = PdfDocument.Merge(pdfs);
return pdf;
}
}
MyViewComponent:
public class MyViewComponent : ViewComponent
{
public IViewComponentResult Invoke(Foo args)
{
return View(args);
}
}
Default.cshtml
#model Foo
<h1>Hello from #Foo.Id<h1>
RenderViewComponentService:
public class RenderViewComponentService
{
private readonly IServiceProvider _serviceProvider;
private readonly ITempDataProvider _tempDataProvider;
private readonly IViewComponentHelper _viewComponentHelper;
public RenderViewComponentService(
IServiceProvider serviceProvider,
ITempDataProvider tempDataProvider,
IViewComponentHelper viewComponentHelper
)
{
_serviceProvider = serviceProvider;
_tempDataProvider = tempDataProvider;
_viewComponentHelper = viewComponentHelper;
}
public async Task<string> RenderViewComponentAsStringAsync<TViewComponent>(object args)
where TViewComponent : ViewComponent
{
var viewContext = GetFakeViewContext();
(_viewComponentHelper as IViewContextAware).Contextualize(viewContext);
// this appears to call InvokeAsync in TViewComponent, but it'll also call Invoke (synchronously) if it's implemented
// see https://learn.microsoft.com/en-us/aspnet/core/mvc/views/view-components?view=aspnetcore-3.1#perform-synchronous-work
var htmlContent = await _viewComponentHelper.InvokeAsync<TViewComponent>(args); // exception is thrown here!
using var stringWriter = new StringWriter();
htmlContent.WriteTo(stringWriter, HtmlEncoder.Default);
var html = stringWriter.ToString();
return html;
}
private ViewContext GetFakeViewContext(ActionContext actionContext = null, TextWriter writer = null)
{
actionContext ??= GetFakeActionContext();
var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
var tempData = new TempDataDictionary(actionContext.HttpContext, _tempDataProvider);
var viewContext = new ViewContext(
actionContext,
NullView.Instance,
viewData,
tempData,
writer ?? TextWriter.Null,
new HtmlHelperOptions());
return viewContext;
}
private ActionContext GetFakeActionContext()
{
var httpContext = new DefaultHttpContext
{
RequestServices = _serviceProvider,
};
var routeData = new RouteData();
var actionDescriptor = new ActionDescriptor();
return new ActionContext(httpContext, routeData, actionDescriptor);
}
private class NullView : IView
{
public static readonly NullView Instance = new NullView();
public string Path => string.Empty;
public Task RenderAsync(ViewContext context)
{
if (context == null) { throw new ArgumentNullException(nameof(context)); }
return Task.CompletedTask;
}
}
}
Exception:
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.AspNetCore.Http.DefaultHttpContext.get_Items()
at Microsoft.AspNetCore.Mvc.Routing.UrlHelperFactory.GetUrlHelper(ActionContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorPageActivator.<>c__DisplayClass4_0.<.ctor>b__0(ViewContext context)
at Microsoft.Extensions.Internal.PropertyActivator`1.Activate(Object instance, TContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorPagePropertyActivator.Activate(Object page, ViewContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorPageActivator.Activate(IRazorPage page, ViewContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
at Microsoft.AspNetCore.Mvc.ViewComponents.ViewViewComponentResult.ExecuteAsync(ViewComponentContext context)
at Microsoft.AspNetCore.Mvc.ViewComponents.DefaultViewComponentInvoker.InvokeAsync(ViewComponentContext context)
at Microsoft.AspNetCore.Mvc.ViewComponents.DefaultViewComponentHelper.InvokeCoreAsync(ViewComponentDescriptor descriptor, Object arguments)
at MyProject.Services.RenderViewComponentService.RenderViewComponentToStringAsync[TViewComponent](Object args) in MyProject\Services\RenderViewComponentService.cs:line ??
at MyProject.Services.PdfService.DoWorkAsync(Foo foo) in MyProject\Services\PdfService.cs:line ??
at MyProject.Services.PdfService.GenerateAsync() in MyProject\Services\PdfService.cs:line ??
at MyProject.Controllers.MyController.Get() in MyProject\Controllers\MyController.cs:line ??
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker
invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task
lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.HeaderPropagation.HeaderPropagationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
I think the problem is how I Contextualize the IViewComponentHelper. But I'm at a loss on how else to do it.
Can you spot anything I'm doing wrong?