我在使用 asp.net 核心依赖项注入(inject)时遇到问题,我无法从 IServiceProvider 解析通用接口(interface)。这是我的设置:
通用接口(interface):
public interface IRequest<out TResponse> {...}
public interface IRequestHandler<TRequest, TResult>
where TRequest : IRequest<TResult> {...}
具体实现:
public class GetUsersQuery : IRequest<IEnumerable<GetUsersResult>> {...}
public abstract class RequestHandler<TRequest, TResult>
: IRequestHandler<TRequest, TResult>
where TRequest : IRequest<TResult> {...}
public class GetUsersQueryHandler
: RequestHandler<GetUsersQuery, IEnumerable<GetUsersResult>> {...}
然后我有一个服务工厂,我是这样注册依赖注入(inject)的:
public static void ConfigureServices(IServiceCollection services)
{
services.AddTransient<IRequestHandler<GetUsersQuery,
IEnumerable<GetUsersResult>>, GetUsersQueryHandler>();
}
我可以像这样成功解析我的处理程序:
var handler =
_services.GetService<IRequestHandler<GetUsersQuery, IEnumerable<GetUsersResult>>>();
但是,我想在这个工厂中有一个通用方法,它接收 IRequest 的具体实现并返回适当的处理程序,而无需事先知道确切的类型,如下所示:
public Task<TResult> Execute<TResult>(IRequest<TResult> request)
{
var handler =
_services.GetService<IRequestHandler<IRequest<TResult>, TResult>>();
return handler.ExecuteAsync(request);
}
然后像这样调用这个方法:
_serviceFactory.Execute(new GetUsersQuery(){});
不幸的是,这不起作用,处理程序未解析且为空。我觉得这应该是可能的。
你能告诉我我做错了什么以及如何实现吗?
最佳答案
此设计可能源自 this博客文章。同一篇博客文章显示了针对您的确切问题的解决方案:
public TResult Process<TResult>(IQuery<TResult> query)
{
var handlerType = typeof(IQueryHandler<,>)
.MakeGenericType(query.GetType(), typeof(TResult));
dynamic handler = container.GetInstance(handlerType);
return handler.Handle((dynamic)query);
}
在您的情况下,这转化为以下内容:
public Task<TResult> Execute<TResult>(IRequest<TResult> request)
{
var handlerType = typeof(IRequestHandler<,>)
.MakeGenericType(request.GetType(), typeof(TResult));
dynamic handler = _services.GetRequiredService(handlerType);
return handler.ExecuteAsync((dynamic)query);
}
关于dynamic
的使用,博文指出:
Unfortunately we need to call the Handle method using reflection (which is done, in this case, using the C# 4.0
dymamic
keyword), because at this point it is impossible to cast the handler instance, since the generic TQuery argument is not available at compile time.
关于c# - .NET Core 依赖注入(inject),解析泛型接口(interface),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/53231845/