I have the following interface I want to implement in a class:
public interface IAgro {
AgroState agroState { get; }
}
The problem is that instead of implementing AgroState in the class using the interface I want my property to implement a different class which inherits from AgroState
public class E1_AgroState : AgroState
{
...
}
public class BasicWalkingEnemy : Entity, IAgro
{
public E1_AgroState agroState { get; }
}
This is something I am used to do in Swift with protocols, for example, but C# compiler complains with
'BasicWalkingEnemy' does not implement interface member 'IAgro.agroState'. 'BasicWalkingEnemy.agroState' cannot implement 'IAgro.agroState' because it does not have the matching return type of 'AgroState'. [Assembly-CSharp]csharp(CS0738)
For now one solution I found is doing it like:
public class BasicWalkingEnemy : Entity, IAgro
{
public AgroState agroState { get { return _agroState; } }
public E1_AgroState _agroState { get; private set; }
}
But I think that is very inelegant.
Is there a better solution to my problem?
Typically the way you'd do this is with explicit interface implementation so that anyone who only knows about your object via IAgro will just see AgroState, but any code that knows it's working with BasicWalkingEnemy will get E1_Agrostate:
// Note: property names changed to comply with .NET naming conventions
public class BasicWalkingEnemy : Entity, IAgro
{
// Explicit interface implementation
AgroState IAgro.AgroState => AgroState;
// Regular property
public E1_AgroState AgroState { get; private set; }
}
Related
tl;dr: I want the list List<ComponentDefinition> in the CellObjectDefinition class to be able to be checked with a type check ICellObjectDefinition<IComponentDefinition>.
ComponentDefinition is unknown at runtime and must therefore be testable with IComponentDefinition.
I have the following class:
public interface IComponentDefinition {}
public class ComponentDefinition : IComponentDefinition {}
public interface ICellObjectDefinition<TCDef>
{
public List<TCDef> Components { get; set; }
}
public class CellObjectDefinition : ICellObjectDefinition<ComponentDefinition>
{
public List<ComponentDefinition> Components { get; set; } = new();
}
I would have liked to keep the type ComponentDefinition in this list as the elements are added dynamically with reflection elsewhere. I want to validate the elements with their associated interfaces.
I don't quite understand why the list doesn't match the interface when I check the list filled with ComponentDefinition elements with ICellObjectDefinition<IComponentDefinition>.
Even an interface without a generic type does not work:
public interface ICellObjectDefinition<IComponentDefinition>
{
public List<IComponentDefinition> Components { get; set; }
}
Here is an executable sample code: https://dotnetfiddle.net/tpiNgJ
Depended on the actual use case you can make your interface covariant:
public interface ICellObjectDefinition<out TCDef> : IObjectDefinition
{
public IReadOnlyCollection<TCDef> Components { get; }
}
Which will require some implementation changes (using explicit interface implementation):
public partial class CellObjectDefinition : ObjectDefinition, ICellObjectDefinition<ComponentDefinition>
{
IReadOnlyCollection<ComponentDefinition> ICellObjectDefinition<ComponentDefinition>.Components => Components; // explicitly implement the interface
public List<ComponentDefinition> Components { get; set; } = new();
}
Full running code - at dotnetfiddle.
I have few classes which inherits from a generic class like FooBasePolicy<TFooTarget>. And I want to cast my derived classes by their base class (not sure if its right way to say it). My classes are:
public class FooTarget{}
public class GTeamTarget : FooTarget{}
public class MTeamTarget : FooTarget{}
public class FooBasePolicy{}
public class FooBasePolicy<TFooTarget> : FooBasePolicy where TFooTarget : FooTarget
{
public virtual TFooTarget SomeFooTarget { get;set; }
}
public class GTeamPolicy : FooBasePolicy<GTeamTarget>
{
public GTeamPolicy()
{
SomeFooTarget = new GTeamTarget();
}
}
public class MTeamPolicy : FooBasePolicy<MTeamTarget>
{
public GTeamPolicy()
{
SomeFooTarget = new MTeamTarget();
}
}
And then I tried to use these this way,
problem is I don't know upfront which TeamTarget it is. It can be G or M.
FooBasePolicy<FooTarget> policy = null;
if (something.Equals("GTEAM"))
{
//This gives me an implicit conversion error. It can't cast.
policy = FromBinary(type, funnelData.Data) as FooBasePolicy<FooTarget>;
}
else if (something.Equals("MTEAM"))
{
policy = FromBinary(type, funnelData.Data) as FooBasePolicy<FooTarget>;
}
FromBinary actually returns a deserialized object.
But it perfectly can cast into FooBasePolicy. But then I miss SomeFooTarget property.
Any idea? Please help.
As the others said, just define an interface:
public interface IFooBasePolicy<out TFooTarget> {
TFooTarget SomeFooTarget { get; }
}
The base class FooBasePolicy now looks like:
public class FooBasePolicy<TFooTarget> : IFooBasePolicy<TFooTarget>
where TFooTarget : FooTarget {
public virtual TFooTarget SomeFooTarget { get; set; }
}
Later you can use the following cast:
policy = ((IFooBasePolicy<FooTarget>)FromBinary(something));
Short explanation:
FooBasePolicy<FooTarget> is not a base class of FooBasePolicy<GTeamTarget>
this can be resolved with covariance: GTeamTarget is a subtype of FooTarget, therefore FooBasePolicy<GTeamTarget> is a subtype of FooBasePolicy<FooTarget>
but covariance is only allowed on interfaces in C#
so you need an interface with a coveriant type declaration
Why am I getting this error and how can I work around it when I CAN'T change the interfaces... (You can copy/paste the code into an empty CS file)
namespace ClassLibrary1
{
public interface IEntity
{
}
public interface IEntitySet<T>
{
}
public class Entity : IEntity
{
}
public class EntitySet<T> : IEntitySet<T>
{
}
public interface IImplementer
{
IEntitySet<IEntity> Set { get; set; }
}
public class Implementer : IImplementer
{
// Error 'ClassLibrary1.Implementer' does not implement interface member 'ClassLibrary1.IImplementer.Set'.
// 'ClassLibrary1.Implementer.Set' cannot implement 'ClassLibrary1.IImplementer.Set'
// because it does not have the matching return type of 'ClassLibrary1.IEntitySet<ClassLibrary1.IEntity>'.
public EntitySet<Entity> Set { get; set; }
}
}
Indeed, your Set method is meant to have a return type of IEntitySet<IEntity>, but you've tried to declare the implementation using EntitySet<Entity>. Two problems there:
IEntitySet isn't EntitySet
IEntity isn't Entity
The implementation signature has to match the interface exactly.
You should probably make IImplementer generic, like this:
public interface IImplementer<T> where T : IEntity
{
IEntitySet<T> Set { get; set; }
}
At that point, you can have:
public class Implementer : IImplementer<Entity>
{
public IEntitySet<Entity> Set { get; set; }
}
You can then write:
var implementer = new Implementer();
implementer.Set = new EntitySet<Entity>();
Is that what you want? If you really need to force Implementer to use EntitySet rather than just any IEntitySet, then you're probably coupling the two ideas too tightly.
You are getting this exception because IImplementer requires an IEntitySet<IEntity> Set property, but your Implementer class is returning an EntitySet<Entity>. EntitySet can be cast to IEntitySet, but IEntitySet cannot be cast to EntitySet, and so the interface implementation fails because you do not satisfy the interface.
Just change public EntitySet<Entity> Set {get; set;} to public IEntitySet<IEntity> Set {get; set;} on your Implementer class.
is there any way to use interfaces as navigation properties in EF6?
I've found related topics for EF4 or earlier where it didn't seem to be possible; generally, inheritance seems to have improved a lot since then, but I haven't found a way to make this specific problem work yet.
Example:
public interface IPerson
{
string name { get; set; }
}
public class Man : IPerson { /* ... */ }
public class Woman : IPerson { /* ... */ }
public interface ICar
{
IPerson driver { get; set; }
}
public class Car : ICar
{
public virtual IPerson driver { get; set; } // This won't map
}
Is this possible in any way? If not, what'd be an advisable way to do this?
Because currently I don't see any way for an interface to have a set-able property whose type is some other interface (the IPerson property of ICar, for example), which kind of strikes me as a very serious design limitation?!
Okay, for those possibly facing the same issue in the future. After more testing around, this is how I'm doing it now.
public interface IPerson
{
string name { get; set; }
}
public abstract class APerson : IPerson
{
public string name { get; set; }
}
public class Man : APerson { /* ... */ }
public class Woman : APerson { /* ... */ }
public interface ICar
{
IPerson driver { get; set; }
}
public class Car : ICar
{
// This maps to the database
public virtual APerson driver { get; set; }
// And this implements the interface
ICar.driver
{
get
{
return (IPerson)driver;
}
set
{
if(!(value is APerson))
throw new InvalidCastException("driver must inherit from APerson");
driver = (APerson)value;
}
}
}
This gets a bit more tricky when having one-to-many / many-to-many relations, for that case I've written a class that inherits from Collection<Interface type>, but also implements ICollection<Abstract base type>, and again throws an exception when someone tries adding/setting any object that doesn't inherit from the abstract base class. It's basically a Collection<IPerson> that's guaranteed to only contain objects inheriting that inherit APerson, if you will.
This solution is definitely not ideal, because it just throws an exception if somebody tries assigning a value to driver that does not inherit from APerson, so no compile-time safety here.
But it's the best solution I could think of so far, if you really want to keep your interfaces separate and self-contained.
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;}
}