I have a design issue and am looking for the best design solution. I have added an example of the issue below.
public interface IVehicle<T>
{
int GetEngineSize();
}
public class Car : IVehicle<Car>
{
public int GetEngineSize()
{
throw new NotImplementedException();
}
public bool HasSpolier()
{
return true;
}
}
public class Bus : IVehicle<Bus>
{
public int GetEngineSize()
{
throw new NotImplementedException();
}
}
public abstract class BaseController<T>
{
public IVehicle<T> Repository { get; set; }
}
public abstract class CarController : BaseController<Car>
{
public CarController()
{
// How can I access the HasSpolier method from the IVehicle<T> without having to cast the Interface to concrete class Car
bool result = Repository.HasSpolier();
}
}
I'm not sure your generics are doing what you want here.
If instead of
IVehicle<T> Repository {get; set;}
You did
T Repository {get; set;}
You could make
public abstract class BaseController<T> where T : IVehicle
To ensure that they're of the IVehicle Interface
Then you'd have a typed repository and get access to your spoiler method.
You're doing IVehicle<Bus> but at least in the sample code, the T is never used in the interface. At this point the T is worthless.
Unless you implement the method in the interface, you can't access it without casting it to another class.
You'd have to cast your Repository to Car.
It would make using your interface pointless as the dependency on the implementation which you're trying to remove is re-introduced.
Also the type parameter on your interface isn't required, you don't use it anywhere else in the interface...
public interface IVehicle
{
int GetEngineSize();
}
Related
I have an interface such as this one:
public interface ITestInterface
{
int a { get; set; }
void DoSomething();
}
Some of my classes are deriving from this interface:
public class OneClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine(this.a.ToString());
}
}
public class AnotherClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine((this.a * 2).ToString());
}
}
Since I now need a (large) common method on all classes derived from my interface, I was trying to provide an additional base class for that:
public class MyBaseClass
{
public void LargeCommonMethod()
{
Console.WriteLine((this.a * 3).ToString()); // no 'a' on base class
}
}
This clearly doesn't work because the base class would also need to implement my interface in order to know about that a field.
I am now asking myself what the best approach would be here:
make MyBaseClass inherit from ITestInterface?
set LargeCommonMethod() to protected and provide all internal data it uses via arguments? (There's actually a lot of these..)
skip the interface all along and replace it with an abstract base class?
...?
C# 8 provides a feature precisely for this scenario.
Your classes all implement an interface
You want to add a method to the interface
You don't want a breaking change to all of the existing classes. If you add a method to the interface all of the classes will break unless you find some way to add the method to all of them. (That includes modifying them all to inherit from a new base class.)
That feature is default interface methods.
You can add your method and a default implementation to the interface:
public interface ITestInterface
{
int a { get; set; }
void DoSomething();
void LargeCommonMethod()
{
Console.WriteLine((this.a * 3).ToString());
}
}
Your existing classes that implement the interface will not break. When cast as the interface, you'll be able to call the method which is defined in the interface. You can still modify any class to provide its own implementation, overriding the interface's default implementation.
For the method to be available the object must be cast as the interface - ITestInterface.
A lot of developers - including myself - found this to be an odd feature. But this is the scenario it's for.
Some documentation
The most common scenario is to safely add members to an interface already released and used by innumerable clients.
If you require a base implementation for a method then an interface is clearly not the way to go.
I would choose an abstract class instead and get rid of the interface. There is no need to complicate the design basically.
The Adapter pattern could fit your Use case, when you want to keep the ITestInterface consistent:
public interface ITestInterface
{
int a { get; set; }
void DoSomething();
}
public class TestInterfaceAdapter : ITestInterface
{
private readonly ITestInterface _testInterface;
public int a {
get => _testInterface.a;
set => _testInterface.a = value;
}
public TestInterfaceAdapter(ITestInterface testInterface)
{
_testInterface = testInterface;
}
public void DoSomething()
{
_testInterface.DoSomething();
}
public void LargeCommonMethod()
{
Console.WriteLine((this.a * 3).ToString());
}
}
public class OneClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine(this.a.ToString());
}
}
public class AnotherClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine((this.a * 2).ToString());
}
}
This is class design question.
I have main abstract class
public abstract class AbstractBlockRule
{
public long Id{get;set;}
public abstract List<IRestriction> Restrictions {get;};
}
public interface IRestriction{}
public interface IRestriction<T>:IRestriction where T:struct
{
T Limit {get;}
}
public TimeRestriction:IRestriction<TimeSpan>
{
public TimeSpan Limit{get;set;}
}
public AgeRestriction:IRestriction<int>
{
public int Limit{get;set;}
}
public class BlockRule:AbstractBlockRule
{
public virtual List<IRestriction> Restrictions {get;set;}
}
BlockRule rule=new BlockRule();
TimeRestriction t=new TimeRestriction();
AgeRestriction a=new AgeRestriction();
rule.Restrictions.Add(t);
rule.Restrictions.Add(a);
I have to use non-generic Interface IRestriction just to avoid specifying generic type T in main abstract class. I'm very new to generics. Can some one let me know how to better design this thing?
Your approach is typical (for example, IEnumerable<T> implements IEnumerable like this). If you want to provide maximum utility to consumers of your code, it would be nice to provide a non-generic accessor on the non-generic interface, then hide it in the generic implementation. For example:
public abstract class AbstractBlockRule
{
public long Id{get;set;}
public abstract List<IRestriction> Restrictions { get; set; }
}
public interface IRestriction
{
object Limit { get; }
}
public interface IRestriction<T> : IRestriction
where T:struct
{
// hide IRestriction.Limit
new T Limit {get;}
}
public abstract class RestrictionBase<T> : IRestriction<T>
where T:struct
{
// explicit implementation
object IRestriction.Limit
{
get { return Limit; }
}
// override when required
public virtual T Limit { get; set; }
}
public class TimeRestriction : RestrictionBase<TimeSpan>
{
}
public class AgeRestriction : RestrictionBase<TimeSpan>
{
}
public class BlockRule : AbstractBlockRule
{
public override List<IRestriction> Restrictions { get; set; }
}
I also showed using a base restriction class here, but it is not required.
The runtime treats IRestriction<TimeSpan> and IRestriction<int> as different distinct classes (they even have their own set of static variables). In your case the only classes common to both IRestriction<TimeSpan> and IRestriction<int> in the inheritance hierarchy are IRestriction and object.
So indeed, having a list of IRestriction is the only sensible way to go.
As a side note: you have a property Limit in there that you might want to access regardless of whether you're dealing with an IRestriction<TimeSpan> or IRestriction<int>. What I would do in this case is to define another property object Limit { get; } on IRestriction, and hide it in the actual implementation. Like this:
public interface IRestriction
{
object Limit { get; }
}
public interface IRestriction<T> : IRestriction
where T : struct
{
new T Limit { get; set; }
}
public class TimeRestriction : IRestriction<TimeSpan>
{
public TimeSpan Limit { get; set; }
// Explicit interface member:
// This is hidden from IntelliSense
// unless you cast to IRestriction.
object IRestriction.Limit
{
get
{
// Note: boxing happens here.
return (object)Limit;
}
}
}
This way you can access Limit as object on all your IRestriction when you don't care what type it is. For example:
foreach(IRestriction restriction in this.Restrictions)
{
Console.WriteLine(restriction.Limit);
}
Interfaces are contracts that need to be followed by the entity that implements the contract.
You have created two contract with the same name IRestriction
As far as I can see, what you are basically may need is a flag for classes that can be restricted, which should implement the IRestriction non-generic interface.
The second interface seems to be restrictable objects that also contain a limit property.
Hence the definition of the second IRestriction interface can be ILimitRestriction or whatever name suits your business needs.
Hence ILimitRestriction can inherit from IRestriction which would mark classes inheriting ILimitRestriction still objects of IRestriction
public abstract class AbstractBlockRule
{
public long Id{get;set;}
public abstract List<IRestriction> Restrictions {get;};
}
public interface IRestriction{}
public interface IRestrictionWithLimit<T>:IRestriction where T:struct
{
T Limit {get;}
}
public TimeRestriction:IRestrictionWithLimit<TimeSpan>
{
public TimeSpan Limit{get;set;}
}
public AgeRestriction:IRestrictionWithLimit<int>
{
public int Limit{get;set;}
}
public class BlockRule:AbstractBlockRule
{
public virtual List<IRestriction> Restrictions {get;set;}
}
I have an interface
public interface IStrategy<T> where T : BaseModel
{
T GetModel(Guid userId);
}
and a concrete class inheriting the interface specifying that it should be a ConcreteModel
public class ConcreteStrategy: IStrategy<ConcreteModel>
{
ConcreteModel GetModel(Guid userId) { ... }
}
Now in the following method I can pass a new instance of ConcreteStrategy and everything works
public class Manager
{
public TModel GetContentModel<TModel>(IStrategy<TModel> strategy, Guid userId)
where TModel : ModelBase
{
return strategy.GetContentModel(userId);
}
}
But if I try to assign it to a property like this I get an error
public class Strategies
{
public static IStrategy<ModelBase> MyStrategy { get; set; }
}
Strategies.MyStrategy = new ConcreteStrategy();
Is there a way I can achieve this in C# ?
I want to be able to make a factory method that encapsulates the logic for which strategy to use and just return an instance of some type of strategy class (like ConcreteStrategy).
The error I am getting is:
Cannot implicitly convert type IStrategy<ModelBase> to IStrategy<ConcreteModel>
You need to make your interface covariant:
public interface IStrategy<out T> where T : BaseModel
Note that it will work only if T only appears in an output position in the interface (which is the case in the code you have shown, but I don't know if it's your real code).
i have another question open here on SO and after thinking about it, i may be approaching this in the wrong way.
i have 4 classes, that have the same properties and methods.
some of the classes, have their own properties and methods ( not overrides of the existing ones ).
currently i create each class as:
public class ClassOne
{
public ClassOne()
{
}
public int ID {get;set;}
// More properties here
public void Set(){
// Do Stuff to save this
}
// More Methods here
}
cant i create one class that will generate all of the 4 classes?
and in the classes themselfs i only create specific properties/methods for that class?
repeating the code seems very odd to me, im sure there must be a way to do this, just dont know how.
Your situation is one of the main reasons why inheritance was invented. So with that, you can write
public class Base
{
// Properties and methods common to all
}
public class ClassOne : Base
{
// Properties and methods specific to ClassOne
}
public class ClassTwo : Base
{
// Properties and methods specific to ClassTwo
}
public class ClassThree : Base
{
// Properties and methods specific to ClassThree
}
public class ClassFour : Base
{
// Properties and methods specific to ClassFour
}
As requested, more code, using interfaces and abstract classes:
An interface is just a blueprint, defining what properties and methods are required to be compatible with other "BaseClasses"
public interface IBaseClass
{
public int ID {get;set;}
public void Set();
}
Abstract classes can contain code, but can not be instantiated, they are form of starting point for a class, but not a complete class themselves.
public abstract class ABaseClass : IBaseClass
{
public int ID {get;set;}
public void Set(){
// Do Stuff to save
}
}
Each class inherits from the abstract class and can then override and implement whatever it wants, customizing it however is necessary.
public class ClassOne : ABaseClass
{
}
public class ClassTwo : ABaseClass
{
}
public class ClassThree : ABaseClass
{
}
public class ClassFour : ABaseClass
{
}
ps. not entirely sure if my syntax is 100% correct
Could you simply make a base class with your properties and inherit from that class?
Why not use inheritance??
public class ClassOne
{
public ClassOne()
{
}
public virtual int ID {get;set;}
// More properties here
public virtual void Set(){
// Do Stuff to save this
}
// More Methods here }
public class ClassTwo : ClassOne
{
public string ClassTwoString { get; set; }
}
public class ClassThree : ClassOne
{
public string ClassThreeString { get; set; }
}
Can you make them all inherit off of the same class? If so, that sounds ideal.
Barring the possibility of making them inherit, you could write an interface that describes the methods and properties which each of them use. Then you can call each instance of the class through the same interface.
Barring again that possibility, you could write a reflective assignor/accessor. But you shouldn't do that.
In this post I talked about using a generic base class to enable me to create repository classes without duplicating loads of basic plumbing code.
Each Repository is accessed through an interface. In the code below, I will only show one of the methods for the sake of brevity:
Interface:
IQueryable<Suggestion> All { get; }
Generic base class
public IQueryable<T> All
{
get { return _unitOfWork.GetList<T>(); }
}
Concrete class (implements the interface and extends the generic base class)
public IQueryable<Suggestion> All
{
get { return _unitOfWork.GetList<Suggestion>(); }
}
I anticipated that I would be able to simply strip the method out of the concrete class, and the compiler would use the generic base class implementation instead and work out that was intended to satisfy the interface. But no!
When I strip the method out I get the old 'does not implement interface member' error.
If I can't do this, have my efforts to use a generic base class not been pointless? Or is there a way around this?
Can you make the interface itself generic then implement a typed version in your concrete class?
public interface IRepository<T>
{
List<T> All { get; }
}
public class Repository<T>
{
public List<T> All
{
get { return new List<T>(); }
}
}
public class SuggestionRepository : Repository<Suggestion>, IRepository<Suggestion>
{ }
I'd still suggest using the generic interface since it will save you from repeating yourself, but this works too.
public interface ISuggestionRepository
{
List<Suggestion> All { get; }
}
public class Repository<T>
{
public List<T> All
{
get { return new List<T>(); }
}
}
public class SuggestionRepository : Repository<Suggestion>, ISuggestionRepository
{ }
Use the virtual keyword and put your interface on your concrete implementation..
public interface IMyInterface<T>
{
IQueryable<T> All { get; }
}
public abstract class MyBaseClass<T> : IMyInterface<T>
{
public virtual IQueryable<T> All
{
get { return _unitOfWork.GetList<T>(); ; }
}
}
public class MyClass : MyBaseClass<Suggestion>, IMyInterface<Suggestion>
{
}