I am trying to define an interface and classes which implement the interface as below. The method defined in the interface accepts a string as argument where myClass2 implementation of the method Execute takes 2 arguments which doesn't follow the interface definition.
That's the problem. How could I define a method within an interface which takes n number of parameters of various type?
Please advice. Thanks.
public interface MyInterface
{
void Execute(string a);
}
public class myClass1 : MyInterface
{
public void Execute(string a)
{
Console.WriteLine(a);
}
}
public class myClass2 : MyInterface
{
public void Execute(string a, int b)
{
Console.WriteLine(a);
Console.WriteLine(b.ToString());
}
}
EDIT: I am thinking of another approach. I appreciate if someone could tell me if this will be a better design.
public interface IParameter
{
Type ParameterType { get; set; }
string Name { get; set; }
object Value { get; set; }
}
public interface MyInterface
{
void Execute(Recordset recordSet, List<IParameter> listParams);
}
public class MyClass : MyInterface
{
public void Execute(Recordset recordSet, List<IParameter> listParams)
{
}
}
I am passing a list of IParameter which holds all the required parameters which need to be sent.
How would the caller know how to call the method, if the interface didn't fix the parameter types?
The closest you can can would be:
public interface MyInterface
{
void Execute(params object[] args);
}
Implementations of the interface would have to then deal with any number of arguments being passed in though - you couldn't have an implementation which only handled a single int parameter, although it could of course throw an exception if args contains anything other than a single int value.
EDIT: Just to be clear, this would rarely be a good design. In some very weakly typed scenarios it may be appropriate, but otherwise, usually it would be worth trying to find something better.
If you can give more information about what you're trying to do, we may be able to help you more.
You can't do this for good reason. Different implementations of interfaces are meant to be used interchangeably. Your proposed design violates this principle. If you want help solving the conflict I think you need to explain what led you to this design.
So you're defining your interface as
public interface MyInterface
{
void Execute(string a);
}
and attempting to implement it as
public void Execute(string a, int b)
{
...
}
That won't work - you're declaring one interface, and attempting to define something else.
What might work (and I can't tell based on your post thus far) is explicit interface implementation - that is, your concrete object could expose an Execute(string, int) method and explicitly implement your interface method. Something like
public class myClass2 : MyInterface
{
public void Execute(string a, int b)
{
...
}
void MyInterface.Execute(string a)
{
...
}
}
That said, I'd strongly advise that you rethink this design. The entire point of interfaces is that they expose a common programmatic surface to the rest of your code - breaking that contract stinks to high heaven, in terms of code-smells.
In addition to #Jon answer: considering that you are implementing an Interface, so you are architect, just don't use an interface but simple base class with overloaded virtual functions and in every concrete class ocerride it in a way you prefer.
EDIT:
I mean something like this: instead of using interface declare base class, a pseudocode!
public class MyCoolBase // a base CLASS and not interface
{
public virtual void Execute(string a)
{
//empty, or NotImplementedException, base on design decision
}
public virtual void Execute(double b)
{
//empty, or NotImplementedException, base on design decision
}
public virtual void Execute(int a, int b)
{
//empty, or NotImplementedException, base on design decision
}
}
public class MyCoolChildOne : MyCoolBase
{
public override void Execute(string a)
{
//concrete implementation
}
}
public class MyCoolChildTwo : MyCoolBase
{
public override void Execute(int a, int b)
{
//concrete implementation
}
}
and so on...
Bad: When you do something like this in the code
MyCoolBase myCoolBase = new MyCoolChildOne ();
myCoolBase...?(); // should be really sure which function you're going to call on this line
Good: You have strong types management, and no more object[] arrays, or multiple inheritance from more then one interface which you must override, instead in this case you cam even avoid it, even if I think it's not so good idea.
By the way, like geeks here said, I don't think your architecture is very reliable, there should be some other solution around for you. We just try to find out the best choice looking on code and question, but real problem can know only you.
Hope this helps.
Regards.
You can do that with weakly typed approach. E.g., you could define an interface that takes objects array:
public intrface MyInterface
{
void Execute(params object[] args);
}
And than you can call any of your concrete class with any arguments:
myClass.Execute("string", 1);
But in this case you violate the main purpose of interfaces, inheritance and compile-time checks.
Another way to implement this is to achieve this is to encapsulate all parameters in additional class hierarchy:
class CommandData
{
public string StringData {get; set;}
}
class ExtendedCommandData : CommandData
{
public int I {get;set;}
}
interface IMyInterface
{
public void Execute(CommandData commandData);
}
class MyClass1 : IMyInterface
{
public void Execute(CommandData commandData);
}
class MyClass2 : IMyInterface
{
// Lets impelment this interface explicitely
void IMyInterface.Execute(CommandData commandData)
{
}
void Execute(ExtendedCommandData extendedData)
{
// now we can access to string and int parameter
}
}
For what it's worth, this might be a great use case for generics.
You define the minimum required parameters as properties of an interface, then inherit where more parameters are required.
Looks quite silly when you're only using 1 parameter in the base interface, but of course this concept could be expanded to more complex types.
public interface MyInterface<T> where T : ParamA
{
void Execute(T paramA);
}
public interface ParamA
{
string ParameterA { get; }
}
public class myClass1 : MyInterface<myClass1.myParamA>
{
public class myParamA : ParamA
{
public string ParameterA { get; set; }
}
public void Execute(myParamA a)
{
Console.WriteLine(a.ParameterA);
}
}
public class myClass2 : MyInterface<myClass2.myParamsAb>
{
public class myParamsAb : ParamA
{
public string ParameterA { get; set; }
public int ParameterB { get; set; }
}
public void Execute(myParamsAb ab)
{
Console.WriteLine(ab.ParameterA);
Console.WriteLine(ab.ParameterB.ToString());
}
}
Related
Maybe this is a dumb question. But, I don't get the point what I am missing.
Given the following class-definition
public abstract class AbstractBaseClass
{
public abstract void Create(AnotherAbstractClass param1);
}
Wheras AnotherAbstractClass is defined
public abstract class AnotherAbstractClass
{
}
with a concrete implementation
public class AnotherConcreteImplementation : AnotherAbstractClass
{
}
I want to be able to have the override of the Create method to use a concrete type:
public class ConcreteImplementation : AbstractBaseClass
{
public override void Create(AnotherConcreteImplementation param1) <-- There is no suitable method for override
{
// param1 is an instance of the concrete implementation
}
public override void Create(AnotherAbstractClass param1) <-- this is working but I'll have to cast on each implementation
{
// param1 is an instance of the abstract class and needs a cast
}
}
Is this simply not possible or is there some way I'm not aware of? Maybe using generics?
Edit #1 (added more context)
I'm trying to achieve/enforce that in a concrete implementation there is only one parameter valid.
Think of it like it's a database-layer. The Create method will create a new entry in the database. As of each table has different values, the create-parameter also has.
The casting inside smells (in my opinion) as of it can be called with any concrete implementation of AnotherAbstractClass.
public class AddressTable : AbstractBaseClass
{
public override void Create(AnotherAbstractClass param1)
{
// cast to concrete instance
var casted = (ConcreteAddressCreate)param1;
}
}
public class CityTable : AbstractBaseClass
{
public override void Create(AnotherAbstractClass param1)
{
// cast to concrete instance
var casted = (ConcreteCityCreate)param1;
}
}
Having an instance of AddressTable I can call
addressIntance.Create(new ConcreteAddressCreate()); // would be okay
on the other hand I can call it
addressIntance.Create(new ConcreteCityCreate()); // would be okay but will fail at runtime with InvalidCastException
Edit #2 (additional info)
It should also be possible to extend the AbstractBaseClass class with more abstract methods later.
So, for me it's more likely to have generic methods instead of an concrete class-implemenation with 200 generic parameters for each method to implement.
It violates the Liskov Substitution Principle so it makes perfect sense you can't do this. Namely, you can't just "have" covariance like this for free:
AbstractBaseClass bcl = new ConcreteImplementation();
bcl.Create(new DifferentImplementationWithoutSecondAbstract());
The contract AbstractBaseClass defines makes Create have to work with any implementation of AbstractBaseClass passed in - if you give a constraint on what can be passed in you've violated the contract it defines.
Like you assumed - you can use generics:
// notice the recursive definition, we require the generic parameter
// to be a generic parameter of itself - allowing AbstractBaseClass
// to not be aware of its subclasses like in the other answers.
public abstract class AbstractBaseClass<T> where T : AbstractBaseClass<T>
{
public abstract void Create(T param1);
}
public class Concrete : AbstractBaseClass<Concrete>
{
public override void Create(Concrete param1)
{
Console.WriteLine("Hello!");
}
}
Yes, you can do that using generics:
public abstract class AbstractBaseClass<T>
where T : AnotherAbstractClass
{
public abstract void Create(T param1);
}
public class ConcreteImplementation : AbstractBaseClass<AnotherConcreteImplementation>
{
public override void Create(AnotherConcreteImplementation param1)
{
}
}
Generics is indeed the way to do it.
public abstract class AbstractBaseClass<TDerivedClass> where TDerivedClass : AnotherAbstractClass
{
public abstract void Create(TDerivedClass param1);
}
And then you can do:
public class ConcreteImplementation : AbstractBaseClass<AnotherConcreteImplementation>
{
public override void Create(AnotherConcreteImplementation param1) // Works because TDerivedClass = AnotherConcreteImplementation
{
...
}
}
Is it possible to define an interface in C# which has a default implementation? (so that we can define a class implementing that interface without implementing that particular default method).
I know extension methods (as explained in this link for example). But that is not my answer because having a method extension like the following, the compiler still complains about implementing MyMethod in MyClass:
public interface IMyInterface
{
string MyMethod();
}
public static class IMyInterfaceExtens
{
public static string MyMethod(this IMyInterface someObj)
{
return "Default method!";
}
}
public class MyClass: IMyInterface
{
// I want to have a default implementation of "MyMethod"
// so that I can skip implementing it here
}
I am asking this because (at least as far as I understand) it is possible to do so in Java (see here).
PS: having an abstract base class with some method is also not my answer simply because we don't have multiple inheritance in C# and it is different from having a default implementation for interfaces (if possible!).
C# v8 and above allows concrete method implementation in interfaces as well. This will allow your concrete implementation classes to not break when you change the interfaces being implemented in future.
So something like this is now possible:
interface IA
{
void NotImplementedMethod(); //method having only declaration
void M()
{
WriteLine("IA.M");
}//method with declaration + definition
}
Please refer to this GitHub issue # 288. Also Mads Torgersen talks about this feature at length in this channel 9 video.
MS Docs - https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/default-interface-methods
I develop games so I often want to have common function for all implementations of an interface but at the same time allow each implementation to do its own thing as well, much like a subclass' virtual / override methods would function.
This is how I do it:
public class Example
{
void Start()
{
WallE wallE = new WallE();
Robocop robocop = new Robocop();
// Calling Move() (from IRobotHelper)
// First it will execute the shared functionality, as specified in IRobotHelper
// Then it will execute any implementation-specific functionality,
// depending on which class called it. In this case, WallE's OnMove().
wallE.Move(1);
// Now if we call the same Move function on a different implementation of IRobot
// It will again begin by executing the shared functionality, as specified in IRobotHlper's Move function
// And then it will proceed to executing Robocop's OnMove(), for Robocop-specific functionality.
robocop.Move(1);
// The whole concept is similar to inheritence, but for interfaces.
// This structure offers an - admittedly dirty - way of having some of the benefits of a multiple inheritence scheme in C#, using interfaces.
}
}
public interface IRobot
{
// Fields
float speed { get; }
float position { get; set; }
// Implementation specific functions.
// Similar to an override function.
void OnMove(float direction);
}
public static class IRobotHelper
{
// Common code for all IRobot implementations.
// Similar to the body of a virtual function, only it always gets called.
public static void Move(this IRobot iRobot, float direction)
{
// All robots move based on their speed.
iRobot.position += iRobot.speed * direction;
// Call the ImplementationSpecific function
iRobot.OnMove(direction);
}
}
// Pro-Guns robot.
public class Robocop : IRobot
{
public float position { get; set; }
public float speed { get; set;}
private void Shoot(float direction) { }
// Robocop also shoots when he moves
public void OnMove(float direction)
{
Shoot(direction);
}
}
// Hippie robot.
public class WallE : IRobot
{
public float position { get; set; }
public float speed { get; set; }
// Wall-E is happy just moving around
public void OnMove(float direction) { }
}
Short Answer:
No, you cannot write implementation of method in interfaces.
Description:
Interfaces are just like contract ,so that the types that will inherit from it will have to define implementation, if you have a scenario you need a method with default implementation, then you can make your class abstract and define default implementation for method which you want.
For Example:
public abstract class MyType
{
public string MyMethod()
{
// some implementation
}
public abstract string SomeMethodWhichDerivedTypeWillImplement();
}
and now in Dervied class:
public class DerivedType : MyType
{
// now use the default implemented method here
}
UPDATE (C# 8 will have support for this):
C# 8 will allow to have default implementation in interfaces
Not directly, but you can define an extension method for an interface, and then implement it something like this
public interface ITestUser
{
int id { get; set; }
string firstName { get; set; }
string lastName { get; set; }
string FormattedName();
}
static class ITestUserHelpers
{
public static string FormattedNameDefault(this ITestUser user)
{
return user.lastName + ", " + user.firstName;
}
}
public class TestUser : ITestUser
{
public int id { get; set; }
public string firstName { get; set; }
public string lastName { get; set; }
public string FormattedName()
{
return this.FormattedNameDefault();
}
}
Edit*
It is important that the extension method and the method that you are implementing are named differently, otherwise you will likely get a stackoverflow.
it is possible in C# 8.0. You can add a method with default implementation. You will have to change your target framework version to latest to use this feature.
As a newbe C# programmer I was reading through this topic and wondered if the following code example could be of any help (I don't even know if this is the proper way to do it). For me it allows me to code default behavior behind an interface. Note that I used the generic type specifiction to define an (abstract) class.
namespace InterfaceExample
{
public interface IDef
{
void FDef();
}
public interface IImp
{
void FImp();
}
public class AbstractImplementation<T> where T : IImp
{
// This class implements default behavior for interface IDef
public void FAbs(IImp implementation)
{
implementation.FImp();
}
}
public class MyImplementation : AbstractImplementation<MyImplementation>, IImp, IDef
{
public void FDef()
{
FAbs(this);
}
public void FImp()
{
// Called by AbstractImplementation
}
}
class Program
{
static void Main(string[] args)
{
MyImplementation MyInstance = new MyImplementation();
MyInstance.FDef();
}
}
}
C# 11 feature - Now official:
Static virtual members in interfaces
Docs saying:
C# 11 and .NET 7 include static virtual members in interfaces.
This feature enables you to define interfaces that include overloaded
operators or other static members.
Once you've defined interfaces with static members, you can use those interfaces as constraints to create generic types that use operators or other static methods.
So you can:
Define interfaces with static members.
Use interfaces to define classes that implement interfaces with operators defined.
Create generic algorithms that rely on static interface methods.
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/static-virtual-interface-members
Prerequisites
You'll need to set up your machine to run .NET 7, which supports C# 11
Consider next situation -
public class Derived : Base{
X(ParamX){} // xx method
X(ParamY){} // xy
}
public abstract class Base {
InvokeX(IParametr param){
...some magic
}
}
public class ParamX : IParametr {}
public class ParamY : IParametr {}
Can I invoke xx method using Derived.InvokeX(ParamX) ?
I know that I can do something like this (checked when InvokeX is in derived class, not shure for abstract):
InvokeX(IParametr #param){
((dynamic) this).X((dynamic) #param);
}
but I am looking for more faster solutions. Can I use in some way System.Runtime.CompilerServices namespace and in particular CallSite Class?
Thanks.
You have an instance of the Expression Problem, an extensibility problem common in most programming languages today. Reflection or dynamic invocation is a way around it, but it is prone to bugs, since you will not notice a mistake in naming or parameter types until you run the code down that specific path.
You want to extend your application to support more types (more implementations of IParametr) and also more operations (in this case more methods using types of parameters).
So basically you will get a matrix of types and operations. E.g.
Type Derived Derived2 ...
ParamX x x
ParamY x
...
The Xes represent requiring the implementation in the type (column) of the operation (row).
To keep the implementation type safe you need to use either the Visitor or the Interpreter pattern. Each has its drawbacks.
The visitor pattern, utilizing double dispatch:
public class Derived : Base {
public override void X(ParamX x) { }
public override void X(ParamY a) { }
}
public abstract class Base : IXVisitor
{
public void Visit(IParametr parameter)
{
parameter.Accept(this);
}
public abstract void X(ParamX x);
public abstract void X(ParamY a);
}
public interface IXVisitor
{
void X(ParamX a);
void X(ParamY a);
}
public interface IParametr
{
void Accept(IXVisitor visitor);
}
public class ParamX : IParametr
{
public void Accept(IXVisitor visitor)
{
visitor.X(this);
}
}
public class ParamY : IParametr
{
public void Accept(IXVisitor visitor)
{
visitor.X(this);
}
}
If you'd like to get really hardcore you can try Object Algebras
This will be generics 101 for many but below is sample code so I can understand better.
public interface IRecordedItemsProcessor<T>
{
ObservableCollection<RecordedItem> Load(string name);
void Save();
RecordedItem Parse(T itemToParse);
}
public class FileLoadingProcessor : IRecordedItemsProcessor<string>
{
public ObservableCollection<RecordedItem> Load(string name)
{
}
public void Save()
{
}
public RecordedItem Parse(string itemToParse)
{
}
}
public class MyClass
{
public MyClass(IRecordedItemsProcessor<T> processor)
{
}
}
The issue is that MyClass needs a dependency on IRecordedItemsProcessor<T> but will not compile as it does not know what T is. How can this be resolved? Making MyClass implement a seems odd as all it needs to do is call Load/Save
Thanks
First solution is the most simple one: lift generic declaration to class level, like
public class MyClass<T>
{
public MyClass(IRecordedItemsProcessor<T> processor)
{
}
}
Then you could instantiate MyClass as following:
var myClass = new MyClass<string>(new FileLoadingProcessor());
Console.WriteLine (myClass);
Second solution is a removing generic input from constructor and inferring types. Then you don't need to specify generic exactly from call. Class declaration will look like:
public class MyClass
{
public void Process<T>(IRecordedItemsProcessor<T> processor)
{
}
}
And then you can call simply
var my = new MyClass();
my.Process(new FileLoadingProcessor());
The Idea is that you always need to specify class-level generics explicitly, but method level generics can be inferred by the compiler.
Third solutions is to encapsulate creation mechanisms inside MyClassFactory. This is quite flexible, but it might seem a little bit complicated, because descendants of IRecordedItemsProcessor<T> don't define generic at class level, so we should go to implemented interfaces and grab there generic types. And only then we can construct Generic MyClass. Listing is given below:
public class MyClassFactory
{
public MyClass<T> MakeMyClassFor<T>(IRecordedItemsProcessor<T> processor)
{
var processorGenericType = processor.GetType()
.GetInterfaces()
.Single(intr=>intr.Name == "IRecordedItemsProcessor`1")
.GetGenericArguments()[0];
var myClassType = typeof(MyClass<>).MakeGenericType(processorGenericType);
return Activator.CreateInstance(myClassType, processor) as MyClass<T>;
}
}
Now you can create MyClass very simply
var myClassFactory = new MyClassFactory();
var res = myClassFactory.MakeMyClassFor(new FileLoadingProcessor());
Console.WriteLine (res);
All of these three approaches have their pros and cons. Consider taking into account the context, in which you are going to use them.
You could do the following:
Create a new interface IRecordedItemsProcessor (non-generic)
Move Load and Save to this IRecordedItemsProcessor
Make IRecordedItemsProcessor<T> inherit from this IRecordedItemsProcessor
Make MyClass expect IRecordedItemsProcessor in its constructor
This makes it clear that MyClass doesn't care what type the processor might be able to parse, or even that it can parse things at all - it only knows that it can save and load.
You could inherit from a non-generic marker interface, this removes the need to know about T in your class:
public interface IRecordedItemsProcessor
{
}
public interface IRecordedItemsProcessor<T> : IRecordedItemsProcessor
{
ObservableCollection<RecordedItem> Load(string name);
void Save();
RecordedItem Parse(T itemToParse);
}
And then you can use any IRecordedItemsProcessor like:
public class MyClass
{
public MyClass(IRecordedItemsProcessor processor)
{
}
}
The generic type, as written, is being declared on the MyClass constructor which means the generic type must be defined at the MyClass level:
public class MyClass<T>
{
public MyClass(IRecordedItemsProcessor<T> processor)
{
}
}
However, if the generic type was declared at a method level, it would only have to be defined at the method level:
public class MyClass
{
public void MyMethod<T>( IRecordedItemsProcessor<T> processor )
{
}
}
EDIT
Based on your comment:
I want a class that can call the Load/Save methods but not be worried
that T is.
Then you'll need 2 interfaces: 1 for the load/save and then one with the parsing. In this case, you could use inheritance:
public interface IRecordedItems
{
ObservableCollection<RecordedItem> Load( string name );
void Save();
}
public interface IRecordedItemsProcessor<T> : IRecordedItems
{
RecordedItem Parse( T itemToParse );
}
public class MyClass : IRecordedItems
{
#region Implementation of IRecordedItems
public ObservableCollection<RecordedItem> Load( string name )
{
throw new NotImplementedException();
}
public void Save()
{
throw new NotImplementedException();
}
#endregion
}
EDIT 2
Based on your gist example, the type dependency could be moved off of the interface and directly into the interface method:
public class RecordedItem {}
public interface IRecordedItemsProcessor
{
ObservableCollection<RecordedItem> Load( string name );
void Save();
RecordedItem Parse<T>( T itemToParse );
}
public class MyClass
{
private readonly IRecordedItemsProcessor _processor;
public MyClass( IRecordedItemsProcessor processor )
{
_processor = processor;
processor.Parse<string>( "foo" );
processor.Parse<int>( 10 );
processor.Parse<RecordedItem>( new RecordedItem() );
}
}
I've the following scenario
I've an Interface
public interface ImyInterface
{
void myInterfaceMethod(string param);
}
I've an Abstract Class
public abstract class myAbstractClass
{
public myAbstractClass()
{
//something valid for each inherited class
}
public void myAbstractMethod<T>(T param)
{
//something with T param
}
}
I've a class that inherits from myAbstractClass and implements ImyInterface
public class myClass : myAbstractClass, ImyInterface
{
public myClass():base()
{}
public void ThisMethodWillNeverCall()
{
// nothing to do
}
}
And, finally, I've a class where I'll create a ImyInterface object. At this point I would call myAbstractMethod, but...
public class myFinalClass
{
public void myFinalMethod()
{
ImyInterface myObj = _myContainer<ImyInterface>();
myObj.???
}
}
Obviously there isn't this method because it isn't declared into the interface.
My solution is the following
public interface ImyInterface
{
void myInterfaceMethod(string param);
void myFakeMethod<T>(T param);
}
public class myClass : myAbstractClass, ImyInterface
{
public myClass():base()
{}
public void ThisMethodWillNeverCall()
{
// nothing to do
}
//--- a fake method
public void myFakeMethod<T>(T param)
{
base.myAbstractMethod<T>(param);
}
}
Is there any other solution better than mine?
Thank you!
First of all, your naming convention is a mess. Read up on the guidelines that Microsoft have made.
It's also hard to tell what you are trying to achieve based on your example.
Back to your question:
You should only access an interface to work with that interface. Don't try to make any magic stuff with classes/interfaces to get them working together. That usually means that the class shouldn't try to implement the interface.
It's better that you create a new interface which have the features that you want and let your class implement both.