[英]Why is typeof(T) != instance.getType()?
I'm working on a factory which shall return a generic implementation of an interface according to a type.我正在开发一个工厂,它将根据类型返回接口的通用实现。
My main question is being illustrated by我的主要问题是由
Why are these typeof(TException).= exception?GetType(), Respectively?为什么这些 typeof(TException).= exception?GetType() 分别是? what do I have to change to have the correct type for TException?我必须更改什么才能获得正确的 TException 类型?
The above code results in a InvalidCast exception because it tries to cast to IDocumedisExceptionHandler<DocumedisException>
instead of IDocumedisExceptionHandler<FhirParsingException>
上面的代码导致 InvalidCast 异常,因为它尝试强制转换为IDocumedisExceptionHandler<DocumedisException>
而不是IDocumedisExceptionHandler<FhirParsingException>
Factory implementation:工厂实施:
internal class DocumedisExceptionHandlerFactory : IDocumedisExceptionHandlerFactory
{
private readonly IDictionary<Type, object> _exceptionHandlers = new ConcurrentDictionary<Type, object>();
public void RegisterExceptionHandler<TException>(IDocumedisExceptionHandler<TException> exceptionHandler)
where TException : DocumedisException
{
_exceptionHandlers.Add(typeof(TException), exceptionHandler);
}
public IDocumedisExceptionHandler<TException> GetDocumedisExceptionHandler<TException>(TException exception)
where TException : DocumedisException
{
_exceptionHandlers.TryGetValue(exception.GetType(), out var exceptionHandler);
return (IDocumedisExceptionHandler<TException>) exceptionHandler;
}
}
Side question: Would there be a better way then using object
as dictionary value?附带问题:有没有比使用object
作为字典值更好的方法?
Registration of the handler in startup:在启动时注册处理程序:
var exceptionHandlerFactory = app.ApplicationServices.GetService<IDocumedisExceptionHandlerFactory>();
exceptionHandlerFactory.RegisterExceptionHandler(new FhirParsingExceptionHandler());
Where FhirParsingExceptionHandler
implements IDocumedisExceptionHandler
FhirParsingExceptionHandler
实现IDocumedisExceptionHandler
internal class FhirParsingExceptionHandler : IDocumedisExceptionHandler<FhirParsingException>
{
public void HandleException(FhirParsingException exception, out HttpStatusCode httpStatusCode, out OperationOutcome.IssueType issueType, out string message)
{
httpStatusCode = HttpStatusCode.BadRequest;
issueType = OperationOutcome.IssueType.Invalid;
message = exception.Message;
}
}
Handler definition (where TException
is contravariant):处理程序定义(其中TException
是逆变的):
public interface IDocumedisExceptionHandler<in TException>
where TException : DocumedisException
{
void HandleException(TException exception, out HttpStatusCode httpStatusCode, out OperationOutcome.IssueType issueType, out string message);
}
And FhirParsingException
extends DocumedisException
: FhirParsingException
扩展DocumedisException
:
public class FhirParsingException : DocumedisException
{
[...]
}
Retrieval of the handler from the middleware:从中间件中检索处理程序:
public async Task Invoke(HttpContext context)
{
try
{
await _next.Invoke(context);
}
catch (Exception ex)
{
if (ex is DocumedisException documedisException)
{
await HandleDocumedisExceptionAsync(context, documedisException);
}
else
{
throw;
}
}
}
private async Task HandleDocumedisExceptionAsync<TException>(HttpContext context, TException ex, MedicationAnalyzerErrorCode? errorCode = null)
where TException : DocumedisException
{
var exceptionHandler = _documedisExceptionHandlerFactory.GetDocumedisExceptionHandler(ex);
[...]
}
typeof(TException)
gives you the compile time type of exception
. typeof(TException)
为您提供exception
的编译时类型。 exception.GetType()
gives you the runtime type of exception
. exception.GetType()
为您提供exception
的运行时类型。 These two need not be the same at all, the only guarantee the compiler makes is that the runtime type of exception
will be assignable to a TException
variable.这两者根本不需要相同,编译器唯一保证的是exception
的运行时类型可以分配给TException
变量。
Consider the following:考虑以下:
class Animal { }
class Turtle: Animal { }
bool CheckTypes<T>(T animal) where T: Animal
{
return typeof(T) == animal.GetType();
}
And now you have:现在你有:
Animal animal = new Turtle();
Feed(animal);
Rest assured, CheckTypes
will return false
; Rest 放心, CheckTypes
将返回false
; the type of the generic type argument is Animal
but the runtime type of animal
is really Turtle
.泛型类型参数的类型是Animal
但 Animal 的运行时类型Turtle
animal
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.