In ISerialized, Resharper is complaining that "Only implementations of 'SerializeShape" are used. Is there something more I should be doing, or is my use of an interface simply over-kill in this instance? My 'requirements' are that any use of class Shape implement SerializeShape. I am attempting to use Interface in a plausible, conventional way, but maybe I am not?
I have an interface of such:
namespace Shapes
{
internal interface ISerialized<in T>
{
string SerializeShape();
}
}
I have a class of such:
using System.Runtime.Serialization;
using Newtonsoft.Json;
namespace Shapes
{
[DataContract]
public class Shape : ISerialized<Shape>
{
[DataMember] public double Perimeter { get; set; }
[DataMember] public double Area { get; set; }
[DataMember] public string ShapeName { get; set; }
[DataMember] public string ShapeException { get; set; }
public string SerializeShape(Shape shape)
{
return JsonConvert.SerializeObject(shape, Formatting.Indented);
}
}
}
In essence if all you do is have a class implement an interface, then there is no use for the interface. It must be referenced inlieu of the class to be of any real benefit. A brief contrived example to explain in code:
public interface IFoo
{
string Bar();
}
public class Foo : IFoo
{
public string Bar()
{
return "Foo";
}
}
public class FooTwo : IFoo
{
public string Bar()
{
Return "FooTwo";
}
}
public class FooBar
{
public void UseFoo()
{
IFoo foo = new Foo();
string result = foo.Bar();
}
public void UseFooTwo()
{
IFoo fooTwo = new FooTwo()
string result = fooTwo.Bar();
}
}
As you can see both methods in FooBar use IFoo instead of the actual implementation of Foo or FooTwo. This allows you (or someone who is implementing a portion of code you wrote) to honor the contract that is IFoo. If they had done FooTwo fooTwo = new FooTwo() then they aren't really getting any benefit of FooTwo implementing IFoo.
I know this is an old question, but I just ran into a similar situation.
It seems as if this warning pops up because you aren't using it from an outside class. Maybe you just haven't created the call to it or, in my case, it's being used only internal to the class implementing the interface.
If this warning pops up as soon as you write the interface or when implementing the interface, then you simply haven't used the method yet. Once you call the method from other code using the interface, then the warning will go away.
In my case, the method was possibly used outside the class at one point, but through iterations of the code, it's now only being used internally. If I wanted to, I could change the method from public to private and remove the method declaration from the interface.
Aside: Because I only have one class implementing the interface, I could delete the interface entirely and just have the implementing class on it's own, which would entirely avoid this warning altogether. However, this interface has several references, including automated tests. Removing the interface is beyond the scope of the changes I need/want to make, so I'm not going to do it.
Is there a way to have a generic field in a class to specialize to a specific type in the constructor?
For example:
class concreteClass1
{
private int a;
public concreteClass1( int a)
{
this.a = a;
}
}
class concreteClass2
{
string b;
public concreteClass2(string b)
{
this.b = b;
}
}
class A<T>
{
private T field;
public A(int x)
{
field = new concreteClass1(x); //error here CS0029
}
public A(string y)
{
field = new concreteClass2(y); //error here CS0029
}
}
So T can be either concreteClass1 or concreteClass1 and their respective ctors will have different signatures.
I would refactor this to use dependency injection. That way the class doesn't contain code to create other classes that it depends on, like myConcreteField = new ConcreteA<T>(4);. Dependency injection is used to keep code from getting tied into difficult knots like this.
(Your example is very, very abstract, which makes it a little difficult. If you use class names like "Concrete" and "Implementation" then it makes the answer harder to read because we use those same words to describe concepts.)
Instead, whatever that Concrete thing is, declare an interface, like
public interface ISomethingThatTheOtherClassNeeds<T>
{
public int MySomething {get;set;}
}
public class SomethingThatTheOtherClassNeeds : ISomethingThatTheOtherClassNeeds<string>
{
public int MySomething {get;set;}
}
Then in your Implementation class:
class Implementation<T>
{
private readonly ISomethingThatTheOtherClassNeeds<T> _something;
public Implementation(ISomethingThatTheOtherClassNeeds<T> something)
{
_something = something;
}
void DoSomething()
{
Console.Write(_something.MySomething.ToString());
}
}
The difference is that instead of being responsible for creating whatever that class is, it's passed to Implementation in the constructor. Implementation doesn't even know what the class is - it just knows that it matches the interface.
This is especially helpful if those other classes in turn depend on more classes. If you're creating them by calling new in your class then that class has to know how to create those classes.
Then to wire it up you would use a dependency injection container like Windsor, Unity, Autofac, and many more. That's not very commonly done with console applications, but I'm guessing this is more experimental than real.
Well this was a bit tricky due to having to convert types. Maybe this will work for you?
class Program
{
static void Main(string[] args)
{
var myImplementation = new Implementation<int>(4);
var myImplementation2 = new Implementation<string>("Hello World");
Console.WriteLine(myImplementation.myConcreteField); // outputs 4!
Console.WriteLine(myImplementation2.myConcreteField); // outputs Hello World
}
}
abstract class MyAbstract<T>
{
public T MySomething;
public MyAbstract(T something)
{
MySomething = something;
}
}
class ConcreteA<T> : MyAbstract<T>
{
public ConcreteA(int something) : base((T)Convert.ChangeType(something, typeof(T)))
{
}
}
class ConcreteB<T> : MyAbstract<T>
{
public ConcreteB(string something) : base((T)Convert.ChangeType(something, typeof(T)))
{
}
}
class Implementation<T>
{
public MyAbstract<T> myConcreteField;
public Implementation(T a)
{
myConcreteField = new ConcreteA<T>(4);
}
void DoSomething()
{
Console.Write(myConcreteField.MySomething.ToString());
}
}
I have an app that accepts plugins using a shared library full of interface classes, but would also like to define some static methods to interact with them that can be overridden by the plugin. I understand the limitations in C# that preclude me from just defining the 'override-able' virtual method as static, but need to know what approach to take nonetheless.
And before anybody marks this as duplicates of 'Declare virtual inside static' questions, I have read all that I can find and none show a workaround for achieving the same results especially considering that I am using interfaces.
public interface IMyClass
{
int MyNum {get;}
}
public static class Extensions
{
public static int NewMyNum(this IMyClass class)
{
return class.MyNum * 2;
}
}
public class FirstClass : IMyClass
{
int MyNum {get {return 5;}}
}
public class AnotherClass : IMyClass
{
int MyNum {get {return 5;}}
public override NewMyNum(this IMyClass class)
{
return class.MyNum * 3;
}
}
public class Main()
{
IMyClass AClassObj = new IMyClass();
console.writeLine(AClassObj.NewMyNum());
IMyClass BClassObj = new IMyClass();
console.writeLine(BClassObj.NewMyNum());
}
I know this is nowhere near compile-able code, but I hope it illustrates what I am trying to achieve without me posting hundreds of line of code.
I was tinkering around with some code and out of curiosity I wanted to know how I can tackle this problem should I ever stumble upon it.
The problem is that I want to have an Interface and a generic (Factory) class that can only create objects that inherit from that interface. There exists concrete classes which implement that interface which are intended to be used by the generic factory; however, I do not want anyone to add to create their own implementations of the interface but I do want them to be able to create their own instances of the objects which inherit from that interface.
I have a piece of code which illustrates what I am trying to do; however, it does not compile because of the inconsistent accessibility. Here is a piece of code which illustrates what I am inquiring about
using System;
using InterfaceTest.Objects;
namespace InterfaceTest
{
class Program
{
static void Main(string[] args)
{
CreatureFactory<Person> p = new CreatureFactory<Person>();
p.Create();
Console.ReadLine();
}
}
}
namespace InterfaceTest.Objects
{
interface LivingCreature
{
int Age { get; set; }
}
public class Person : LivingCreature
{
public int Age
{
get;
set;
}
}
public class CreatureFactory<T> where T : class, LivingCreature, new()
{
public T Create()
{
return new T();
}
}
}
Consider the following class and interfaces:
public interface A { string Property { get; set; } }
public interface B { string Property { get; set; } }
public interface C : A, B { }
public class MyClass : C
{
public string Property { get; set; }
}
Looks simple, right? Now consider the following program:
static void Main(string[] args)
{
MyClass myClass = new MyClass();
myClass.Property = "Test";
A aTest = myClass;
B bTest = myClass;
C cTest = myClass;
aTest.Property = "aTest";
System.Console.WriteLine(aTest.Property);
bTest.Property = "bTest";
System.Console.WriteLine(bTest.Property);
cTest.Property = "cTest";
System.Console.WriteLine(cTest.Property);
System.Console.ReadKey();
}
Looks okay, but it will not compile. It gives me an Ambiguity exception:
Why isn't C# able to figure this out? Is what I'm doing crazy from an architectural point of view? I'm trying to understand the why (I know it can be solved with casting).
EDIT
The problems arose when I introduced interface C. When I use MyClass : A, B I've got no problems at all.
FINAL
Just finised a blog about the subject: Interface Ambiguity and Implicit Implementation.
In short because it's ambiguous indeed.
Now more detailed story. As you've already seen there is explicit interface implementation, so you can have two different implementations for A.Property and B.Property and when you have only C there is no way you can tell if implementations are the same or not. Since C# "philosophy" is not to guess what you meant, but make you state it more clear when necessary, compiler does not choose either A.Property or B.Property, but reports an error.
You need explicit interface implementation:
public interface A { string Property { get; set; } }
public interface B { string Property { get; set; } }
public interface C : A, B { }
public class MyClass : C
{
string B.Property { get; set; }
string A.Property { get; set; }
}
When it comes time to call them you are going to have to do:
MyClass c = new MyClass();
Console.WriteLine("Property A is ": ((A)c).Property);
Why don't you do:
public class MyClass : C
{
string B.Property { get; set; }
string A.Property { get; set; }
string B { get { return B.Property; } set { B.Property=value; } }
string A { get { return A.Property; } set { A.Property=value; } }
}
And it should be noted this is bad design, if you are going to expose an interface C, make sure you find a better way to expose A/B.Property.
What's to figure out? cTest is of type "C", and it inherits "Property" from two different classes; the compiler doesn't know which one you want. This sort of behavior is inherited from C++; it's the classic example of "why multiple inheritance is a Pandora's box."
Other object-oriented languages -- Java is a notable example -- avoid this problem by definition : like-named/like-signatured methods are fused in a common descendent.
When you inherit from a single interface the compiler can determine exactly which method you are interested in implementing when you add the new method.
However when multiple interfaces have the same method, the underlying (and correct) assumption is that each interface expects a DIFFERENT implementation for the method, due to the fact that those methods or properties are defined on different interfaces.
So the compiler tells you that these different interfaces require an explicit implementation for each of these properties.
The fact that two interfaces share the same NAME for a property or method is arbitrary - there is no reason to assume that they share anything OTHER then the name, so the compiler protects you from making the mistake of implicitly treating them in the same way.
It is not simple, and it doesn't look simple either. In case of a name collision between two interfaces, .NET needs to ask you which interface are you trying to implement. Its way to ask you this is via the ambiguity error.
If you didn't have this kind of errors, you would end up implementing interfaces by chance.
you need to explicity implement both properties from each interface:
public class MyClass : C
{
string A.Property { get; set; }
string B.Property { get; set; }
}
Because what you are doing is not right. A and B are clashing and have the same name for the property... you need to use Explicit implementation of interface.
Reference here.
There are a lot of answers, and all of them are right, as explicit interface implementation is the answer to your problem.
I'll try to clarify the motivation behind this design with a somewhat convoluted example:
Let's say I have an interface for people that run (with possible implementations like LongDistanceRunner, Jogger, MarathonMan, etc)
public interface IRunner
{
void Run();
}
and an interface for devices that can be turned on and ran (with possible implementations BathTub, Application, Dishwasher, etc)
public interface IRunnable
{
void Run();
}
Now I want to create and interface for a IMusicallJogger (implementations like JoggerWithIpod,BoomBoxJogger, etc)
public interface IMusicalJogger : IRunner, IRunnable {}
public class BoomBoxJogger : IMusicalJogger
{
// code here
}
BoomBoxJogger bbJogger = new BoomBoxJogger();
Now, when I say bbJogger.Run() what should my object do? Should it start running across the park, or should it turn on the boombox, or both, or something else entirely? If I implement both the class and the callsite, it might be obvious that I want my joggers to do both, but what if I control just the callsite? And what if there are other implementations of the interface that do something else? And what if my jogger starts running across the park, when it's used in a context where it is considered like a device (through casting).
That's where explicit interface implementation comes into play.
I have to define my class like this:
public class BoomBoxJogger : IMusicalJogger
{
void IRunner.Run() //implementation of the runner aspect
{
Console.WriteLine("Running through the park");
}
void IRunnable.Run() //implementation of the runnable aspect
{
Console.WriteLine("Blasting out Megadeth on my boombox");
}
public void Run() //a new method defined in the class itself
{
Console.WriteLine("Running while listening to music");
}
}
and then, when I call, I have to specify what aspect of my jogger I want to use:
BoomBoxJogger bbJogger = new BoomBoxJogger();
((IRunner).bbJogger).Run(); // start running
((IRunnable).bbJogger).Run(); // blast the boombox
//and of course you can now do
bbJogger.Run //running while listening
((IMusicalJogger)jogger).Run(); //compiler error here, as there is no way to resolve this.
Hope I helped clarify the concept.