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());
}
}
Related
I am little stuck with achieving something with multiple generic parameters. I have a service interface which will take a messagecontext interface as input to method.
public interface IService<T,U> where T : IMessageContext<U>
{
void ExecuteJob(T data);
bool CancelJob();
}
Then an abtract class which implements the interface.
public abstract class AbstractService<T,U> : IService<T,U> where T: IMessageContext<U>
{
public virtual bool CancelJob()
{
return true;
}
public abstract void ExecuteJob(T data);
}
The IMessage interface and default implementation is as shown below
public interface IMessageContext<U>
{
U Data { get; set; }
}
public class DefaultMessageContext : IMessageContext<string>
{
public string Data { get ; set; }
}
In this case, if we inherit the AbstractService class, it would be like below with the Generic parameters for T as DefaultMessageContext & U as string
public class ConcereteService : AbstractService<DefaultMessageContext,string>
{
public override void ExecuteJob(DefaultMessageContext data)
{
//Execute the job
}
}
Is there a way where I can just only mention the type for T as DefaultMessageContext as the type of U is already set in the class while implementing IMessageContext
Something like this
public class ConcereteService : AbstractNewService<DefaultMessageContext>
{
public override void ExecuteJob(DefaultMessageContext data)
{
//Execute the job
}
}
I could introduce another layer of abstraction where the type of U is set as string and only keep T open for implementation like AbstractStringService<T> : AbstractService<T,string>. But I don't want to do that.
Is there any other way to achieve it.
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;}
}
Im not sure if it is possible. I am running into a unique issue dealing with a clients api.
I am needing to extend a class and add a bool property that does not exist in the base class.
below is an example of what I am trying to accomplish.
public class baseClass
{
//.. No Editable Access
}
public class Extended
{
public bool flaggedAsDeleted(this baseClass bc)
{
//Idealy was looking for get; set; but I know that don't work
return true;// Need to know if possible to set property on baseClass or Alternative
}
public void flagAsDeleted(this baseClass bc)
{
flaggedAsDeleted = true;
}
}
public class program
{
public void doit()
{
baseClass bc = new baseClass();
bc.flagAsDeleted();
}
}
If you're trying to actually extend a class, you do it like this:
public class BaseClass
{
//.. No Editable Access
}
public class Extended : BaseClass
{
public bool FlaggedAsDeleted { get; set; }
}
If you're trying to add data to an existing class, you have two options:
Inheritance - as seen above.
Encapsulation - create a new object that holds an instance of the type you're adding to.
C# provides a feature called Extension Methods, which allows you to seemingly add methods to existing classes. However, these are really just syntactic sugar, as you're still constrained to the class's public API.
public class BaseClass
{
public int Value { get; set; }
}
public static class ExtensionMethods
{
public static void Increment(this BaseClass b)
{
b.Value += 1;
}
}
Extension methods do not allow you to add data to an existing class though.
This is not unique. This is a common problem solved using a Design Pattern called decorator.
I'm using Ninject.Extensions.Interception (more specifically, InterceptAttribute) and Ninject.Extensions.Interception.Linfu proxying to implement a logging mechanism in my C# app, but I am facing some problems when a proxied class implements several interfaces.
I've a class which implements an interface and inherits from an abstract class.
public class MyClass : AbstractClass, IMyClass {
public string SomeProperty { get; set; }
}
public class LoggableAttribute : InterceptAttribute { ... }
public interface IMyClass {
public string SomeProperty { get; set; }
}
public abstract class AbstractClass {
[Loggable]
public virtual void SomeMethod(){ ... }
}
When I try to get an instance of MyClass from ServiceLocator, the Loggable attribute causes it to return a proxy.
var proxy = _serviceLocator.GetInstance<IMyClass>();
The problem is the proxy returned only recognizes the AbstractClass interface, exposing SomeMethod(). Consequentially, I receive an ArgumentException when I try to access the inexistent SomeProperty.
//ArgumentException
proxy.SomeProperty = "Hi";
In this case, is there a way of using mixin or some other technique to create a proxy exposing multiple interfaces?
Thanks
Paulo
I ran in a similar problem and i did not found a elegant solution with only ninject means. So i tackled the problem with a more basic pattern from OOP: composition.
Applied to your problem something like this would be my suggestion:
public interface IInterceptedMethods
{
void MethodA();
}
public interface IMyClass
{
void MethodA();
void MethodB();
}
public class MyInterceptedMethods : IInterceptedMethods
{
[Loggable]
public virtual void MethodA()
{
//Do stuff
}
}
public class MyClass : IMyClass
{
private IInterceptedMethods _IInterceptedMethods;
public MyClass(IInterceptedMethods InterceptedMethods)
{
this._IInterceptedMethods = InterceptedMethods;
}
public MethodA()
{
this._IInterceptedMethods.MethodA();
}
public Method()
{
//Do stuff, but don't get intercepted
}
}
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();
}