I have the next scenario:
public class RequestBase { }
public class ResponseBase { }
public interface IService<TRequest, TResponse>
where TRequest : RequestBase where TResponse : ResponseBase
{
TResponse Execute(TRequest request);
}
public class MyRequest : RequestBase { }
public class MyResponse : ResponseBase { }
public class MyService : IService<MyRequest, MyResponse>
{
public MyResponse Execute(MyRequest request)
{
return new MyResponse();
}
}
now i am creating factory that will create my service:
class ServicesFactory
{
public IService<RequestBase, ResponseBase> Create()
{
var service = new MyService();
return (IService<RequestBase, ResponseBase>)service;
}
}
The problem is that the casting throw exception.
How can I cast the derived type to the base type?
Make your interface covariant on TResponse:
public interface IService<TRequest, out TResponse>
and you'll be able to convert MyService to IService<MyRequest, ResponseBase>. Note that it isn't possible to convert to IService<RequestBase, ResponseBase>, because not all RequestBases are MyRequests.
That said, you can decorate MyService with a different class that will check at runtime whether passed in RequestBase is actually MyRequest. This, of course, violates LSP if the interface expects any RequestBase.
Related
I don't want to make class B generic because there lots classes inheriting from class B. How to use the method "GetSomeData" of the generic class "classA" in a non generic class?
Here's my code:
public abstract class classA<T> : IInterface<T>
where T : new()
{
public String GetSomeData (Guid ID)
{
return somestring;
}
}
public abstract class ClassB : InterfaceB
{
//Use GetSomeData(Guid ID) here
}
what is the best way to invoke GetSomeData in class B?
First of all, your code doesn't look clean itself. C# coding conventions are not met & not all the components that are used present.
But to anser your question, you need to specify the concrete type T before using generic methods/classes.
For example working code may look like this:
public abstract class GenericParent<T>
where T : new()
{
public string GetSomeData(Guid id) => string.Empty;
}
// Non abstract type, to create be able to create an instance
public class GenericChild<T> : GenericParent<T> where T : new()
{
}
public abstract class ClassB
{
public void DoSomething()
{
// Creating instance of a generic type, specifying concrete T (in this case of type SomeClass)
var instance = new GenericChild<SomeClass>();
instance.GetSomeData(Guid.Empty);
}
}
// An example of type, that meets the "where" condition of T in the generic type
public class SomeClass
{
}
As per OOP principals Abstract classes can not be instantiated.
They could only be Inherited. Well there are couple of ways how you can access the instance variables and methods from the Abstract class as follows.
Make a sub-class inheriting the Abstract class; Create an object of sub-class and access all the Instance Variables and Methods.
public abstract class classA<T> : IInterface<T>
where T : ITask, new()
{
public String GetSomeData (Guid ID)
{
return somestring;
}
}
public class ChildOfClassA : ClassA<SomeType_of_Type_ITask>
{
}
public abstract class ClassB : InterfaceB
{
//Use GetSomeData(Guid ID) here
ChildOfClassA obj = new ChildOfClassA();
string result = obj.GetSomeData(Guid.NewGuid());
}
Make that method Static if its not tightly coupled to instance of the class. and then you can use it with ClassName.MethodName
public abstract class classA<T> : IInterface<T>
where T : ITask, new()
{
public **static** String GetSomeData (Guid ID)
{
return somestring;
}
}
public abstract class ClassB : InterfaceB
{
//Use GetSomeData(Guid ID) here
string result = classA.GetSomeData(Guid.NewGuid());
}
You can inherit this Abstract class in the class you want to use it and directly access it by base.MethodName or directly MethodName.
public abstract class classA<T> : IInterface<T>
where T : ITask, new()
{
public string GetSomeData (Guid ID)
{
return somestring;
}
}
public abstract class ClassB : ClassA<SomeType_of_Type_ITask>, InterfaceB
{
//Use GetSomeData(Guid ID) here
string result = [base.]GetSomeData(Guid.NewGuid()); //[base.] is optional even you can override this function or overload it.
}
In case 1 and 3 you will have to pass generic argument in order to inherit the Abstract class as in your case Abstract class accepts generic arguments.
For one week I'm getting the below type missmatch error. I search through the internet, looked at how to use generics, but I couldn't find what I'm doing wrong. could anyone please tell me how to fix this problem
static void Main(string[] args) {
JSonHttpClient httpClient;
// ....
public ListAlertsResponse ListAlerts(ListAlertsRequest listAlertsRequest) {
//HERE COUSES THE ERROR !!!
return (ListAlertsResponse)httpClient.DoGetRequest(listAlertsRequest);
}
}
error:
Error 5 Argument 1:
cannot convert from 'ListAlertsRequest' to BaseRequest<BaseResponse>'
My classes and interfaces
public class JsonHttpClient {
public BaseResponse DoGetRequest(BaseRequest<BaseResponse> request) {
return new BaseResponse(...) }
}
public interface Request {}
public interface Response {}
public abstract class BaseResponse : Response {}
public abstract class BaseRequest<T> : Request where T : BaseResponse {}
public class ListAlertsResponse : BaseResponse {}
public class ListAlertsRequest : BaseRequest<ListAlertsResponse> {}
You're sending a type ListAlertsRequest to DoGetRequest which needs a parameter of type BaseRequest<BaseResponse>. ListAlertsRequest is not of type BaseRequest<BaseResponse>
listAlertsRequest is not a subclass of BaseRequest
public class JsonHttpClient
{
public BaseResponse DoGetRequest<T>(BaseRequest<T> request) where T : BaseResponse
{
return new BaseResponse(...)
}
}
DoGetReq returns BaseResponse:
public BaseResponse DoGetRequest(BaseRequest request)
so either return the actual type you're hoping for (ListAlertsResponse), or write a routine to convert it, or (best imo), have ListAlertsResponse take BaseResponse in its constructor and grab whatever info is needed at that point.
A little improvement of T McKeown's answer:
public TResponse DoGetRequest<TResponse>(BaseRequest<TResponse> request)
where TResponse : BaseResponse
{
return default(TResponse);
}
Since BaseRequest is constrained by parameter T, you should put constraint on generic method too. Also, you can omit casting from caller code, using generic return type:
// response is already ListAlertsResponse
var response = httpClient.DoGetRequest(listAlertsRequest);
DoGetRequest returns BaseResponse which you can't cast to a type of a derived class ListAlertsResponse. Think about the following, what if:
public class BaseResponse
{
public int NumberA { get; set; }
}
And the derived class had
public class ListAlertsResponse : BaseResponse
{
public string StringB { get; set; }
}
What do you think this cast will set test.StringB to?
var test = (ListAlertsResponse)httpClient.DoGetRequest(listAlertsRequest);
The runtime doesn't know how to properly cast this for you, if you want to do this, you need to create a converter yourself, or better yet, not do this, you can cast into a base class, but not the other way around.
Basically, I'm trying to do something like this:
SomeRequest request = new SomeRequest();
SomeResponse response = request.GetResponse();
List<Stuff> stuff = response.GetData();
SomeRequest and SomeResponse are classes that both implement the IRequest and IResponse interfaces respectively:
public class SomeRequest : IRequest<SomeResponse>
{
public SomeResponse GetResponse() { ... }
}
public class SomeResponse : IResponse<List<Stuff>>
{
public List<Stuff> GetData() { ... }
}
My IResponse interface looks like this:
public interface IResponse<T>
{
T GetData();
}
The issue I'm running into is with my IRequest interface. I want my IRequest interface's generic (T) to be of type IResponse< T >.
public interface IRequest<T> where T : ?????
{
T GetResponse();
}
I can't figure out what I'm supposed to put after the "where T".
I found two solutions here: C# generic "where constraint" with "any generic type" definition?
The first solution is to specify IResponse< T> generic's type in IRequest like so:
public interface IRequest<T, U> where T : IResponse<U>
but that seems weird because the Request should only have knowledge of the Response and not the type that Response is supposed to return on GetData().
The second option is to create a non-generic interface IResponse and use that in IRequest's generic type constraint, which would look something like this:
public interface IResponse { }
public interface IResponse<T> { ... }
public interface IRequest<T> where T : IResponse
{
BaseResponse GetResponse();
}
This solution however caused a compile error in my SomeRequest class:
public class SomeRequest : IRequest<SomeResponse>
{
public SomeResponse GetResponse() { ... }
}
Error CS0738: SomeRequest does not implement interface member IRequest<SomeResponse>.GetResponse() and the best implementing candidate SomeRequest.GetResponse() return type SomeResponse does not match interface member return type IResponse
So now I'm out of ideas. Any help would be greatly appreciated!
How about:
public interface IRequest<T>
{
IResponse<T> GetResponse();
}
This way you can say things like: new MyRequest().GetResponse().GetData() without having to worry about the exact intermediate response type.
Is it possible you're overcomplicating it? Here's how I implemented what I think you want to do:
public interface IRequest<T>
{
T GetResponse();
}
public interface IResponse<T>
{
T GetData();
}
public class MyRequest : IRequest<MyResponse>
{
public MyResponse GetResponse()
{
return new MyResponse();
}
}
public class MyResponse : IResponse<MyData>
{
public MyData GetData()
{
return new MyData() { Name = "Test" };
}
}
public class MyData
{
public string Name { get; set; }
}
I have my two interfaces, my two implementations of those interfaces, and I can consume them like the following:
MyRequest request = new MyRequest();
MyResponse response = request.GetResponse();
MyData data = response.GetData();
I'm trying to implement the best code re-usability. The problem is that I can't access the base method located in the Base Abstract class form the Main Program through the repository.
If you go through the example below you will see a sample code of my situation.
So my question is how can I access methods located in the base abstract class from the main program.
Classes/Interfaces
public abstract class BaseEntity
{
public override abstract String ToString();
}
public abstract class BaseClass<T> where T : BaseEntity
{
public T GetById(int id)
{
//Dummy Code
return new T();
//
}
}
public interface IFooRepository
{
IList<Foo> GetOrderedObjects();
}
public interface FooRepository : BaseClass<Foo>, IFooRepository
{
public IList<Foo> GetOrderedObjects()
{
//GetById method is accessible from the repository - Fine
var obj = this.GetById(5);
//Dummy Code
return new List<Foo>();
//
}
}
//Main App
public class void Main()
{
private IFooRepository _fooRepository;
public void ProgramStartsHere()
{
//This is ok.
var list = _fooRepository.GetOrderedObjects();
//Problem is here - GetById method is not accessible from the main program through the FooRepository
var obj = _fooRepository.GetById(10);
}
}
GetById isn't defined in the interface
I would make an
public interface IBaseRepository<T> where T : BaseEntitiy {
T GetById<T>(int id);
}
Then BaseClass implements IBaseRepository<T>
and IFooRepository inherits from IBaseRepository<Foo>
EDIT :
A full example, similar to #Olivier J-D one, with idea (maybe wrong), that GetOrderedObject may be same for all your entities.
public abstract class BaseEntity
{
public override abstract String ToString();
}
//all generic methods
public interface IRepositoryBase<T>
where T : BaseEntity, new()
{
T GetById(int id);
IList<T> GetOrderedObjects();
}
//all methods specific to foo, which can't be in a generic class
public interface IFooRepository :IRepositoryBase<Foo>
{
void Update(Foo model);
}
//implementation of generic methods
public abstract class BaseClass<T> : IRepositoryBase<T>
where T : BaseEntity, new() // ===> Add new() constraint here
{
public T GetById(int id)
{
return new T();
}
public IList<T> GetOrderedObjects() {
var obj = this.GetById(5);
//Dummy Code
return new List<Foo>();
//
}
}
//implementation of Foo specific methods
public class FooRepository : BaseClass<Foo>, IFooRepository
{
public void Update(Foo model) {
//bla bla
}
}
Add a new Interface which declares the GetById method and let IFooRepository and BaseClass<T> inherit from it. You will have to add a generic type parameter to IFooRepository as well. (I renamed IFooRepository to IRepository<T>, since it is generic now.)
public abstract class BaseEntity
{
public override abstract String ToString();
}
public interface IRetriever<T>
where T : BaseEntity, new()
{
T GetById(int id);
}
public interface IRepository<T> : IRetriever<T>
where T : BaseEntity, new()
{
IList<T> GetOrderedObjects();
}
public abstract class BaseClass<T> : IRetriever<T>
where T : BaseEntity, new() // ===> Add new() constraint here
{
public T GetById(int id)
{
return new T();
}
}
public class FooRepository : BaseClass<Foo>, IRepository<Foo>
{
public IList<Foo> GetOrderedObjects()
{
var obj = this.GetById(5);
return new List<Foo>();
}
}
This will work fine then
IRepository<Foo> _fooRepository = new FooRepository();
var list = _fooRepository.GetOrderedObjects();
var obj = _fooRepository.GetById(10);
Your _fooRepository inherits from IFooRepository, not FooRepository, so it doesn't have access to GetById(10);
You must expose the GetById method in your repository interface.
public interface IFooRepository
{
IList<Foo> GetOrderedObjects();
Foo GetById(int id);
}
Alternatively you can use a type parameter constraint, as stated by Raphaël Althaus
IFooRepository doesn't inherit from BaseClass, so you have to cast _fooRepository to FooRepository. Then you can access GetById()
Cast it to the base class.
var obj = ((BaseClass<Foo>)_fooRepository).GetById(10);
I am trying to create a function like
public static TResponse Run<TService, TResponse>(Controller mvcController, IServiceController serviceController, Func<TService, TResponse> action, bool suppressErrors)
where TService : ICommunicationObject
where TResponse : ResponseBase<TResponse>
{
TResponse response = serviceController.Run<TService, TResponse>(action);
if (!suppressErrors)
response.Result.Errors.ToList().ForEach(i => mvcController.ModelState.AddModelError(UniqueKey.ValidationMessage, i.Message));
return response;
}
and class has been defined as
[DataContract]
public class ResponseBase<T> where T: new()
{
public ResponseBase()
{
Result = new Result<T>();
}
[DataMember]
public Result<T> Result { get; set; }
}
I am getting the compilation error as TResponse must be a non abstract type with a parameterless constructor in order to use it as parameter TResponse
Any help would be appreciated..
Although you've defined the new() constraint for T in ResponseBase<T>, the compiler requires you to declare the same constraint in other classes that use ResponseBase<T> generically.
All you have to do is add the new() constraint to TResponse in your method:
public static TResponse Run<TService, TResponse>(Controller mvcController, IServiceController serviceController, Func<TService, TResponse> action, bool suppressErrors)
where TService : ICommunicationObject
where TResponse : ResponseBase<TResponse>, new()