I want to create an interface which can handle multiple other object of one interface.
I tried using the interface in the interface and using an object in the new class.
public interface IObject
{
double Value { get; set; }
}
public class FirstObject: IObject
{
double Value { get; set; }
}
public class SecondObject: IObject
{
string Titel { get; set; }
double Value { get; set; }
}
public interface ICollection
{
IObject[] Values { get; set; }
}
public class Collection: ICollection
{
SecondObject[] Values { get; set; }
}
Now I get the error, that my Collection doesn't implement the IObject[] Values member.
I thought when I use an object (SecondObject) which is implementing from the interface IObject the Collection should handle this.
What am I doing wrong and how can I solve this?
You might be off better here using generics:
public interface ICollection<T> where T : IObject
{
T[] Values { get; set; }
}
public class Collection : ICollection<SecondObject>
{
public SecondObject[] Values { get; set; }
}
The reason that it doesn't work now, is that the signature should match exactly. That means the Values should be an array of IObject, which it isn't. Using generics you can solve this, while keeping the type constraint.
A second, but inadvisable solution would be using an explicit interface implementation:
public SecondObject[] Values { get; set; }
IObject[] ICollection.Values
{
get
{
return this.Values;
}
set
{
this.Values = value?.Cast<SecondObject>().ToArray();
}
}
Related
I have the following scenario that involves a couple of interfaces as below
internal interface ITranslation
{
string LanguageCode { get; set; }
string Title { get; set; }
}
Any object that hold translations will implement the ITranslation interface. Some of these objects can have synonyms as well, so I have another interface
internal interface ITranslationWithSynonmys : ITranslation
{
IList<string> Synonyms { get; set; }
}
Next step I have defined ITranslatable<T> interface for any object that has translations and can be translated in different languages
internal interface ITranslatable<T> where T : ITranslation
{
IList<T> Translations { get; set; }
}
while when there are synonyms involved the ITranslatableWithSynonyms<T> looks like this
internal interface ITranslatableWithSynonyms<T> : ITranslatable<T> where T : ITranslationWithSynonmys
{
IList<T> SynonymTanslations { get; set; }
}
Concrete implementations of ITranslation and ITranslationWithSynonmys would be
internal class BaseTranslation : ITranslation
{
public string Title { get; set; }
public string LanguageCode { get; set; }
}
internal class BaseTranslationWithSynonmys : ITranslationWithSynonmys
{
public IList<string> Synonyms { get; set; }
public string LanguageCode { get; set; }
public string Title { get; set; }
}
while an entity that can be translated would be
internal class TranslatableEntity : ITranslatable<ITranslation>
{
public IList<ITranslation> Translations { get; set; }
}
and if it has synomys
internal class TranslatableWithSynonymsEntity : ITranslatableWithSynonyms<ITranslationWithSynonmys>
{
public IList<ITranslationWithSynonmys> SynonymTanslations { get; set; }
public IList<ITranslationWithSynonmys> Translations { get; set; }
}
Next, I'm creating a service that can translate any object that implements ITranslatable<T> and I have defined it as
internal class TranslationService
{
internal string Translate(ITranslatable<ITranslation> translatable, string languageCode)
{
// It will iterate through the Translations list to find the correct translation
return string.Empty;
}
}
Now, when I try to use the service, I'm writting
var translationService = new TranslationService();
var translatableEntity = new TranslatableEntity();
var translatableWithSynonymsEntity = new TranslatableWithSynonymsEntity();
string x = translationService.Translate(translatableEntity, "en");
string y = translationService.Translate(translatableWithSynonymsEntity, "en");
and here the last line translationService.Translate(translatableWithSynonymsEntity, "en") fails to compile with error CS1503: Argument 1: cannot convert from 'TestInheritance.TranslatableWithSynonymsEntity' to 'TestInheritance.ITranslatable<TestInheritance.ITranslation>'
It's true that TranslatableWithSynonymsEntity doesn't implement ITranslatable<ITranslation>, but it implements ITranslatableWithSynonyms<ITranslationWithSynonmys> with both ITranslatableWithSynonyms<T> inheriting from ITranslatable<T> and ITranslationWithSynonmys inheriting from ITranslation.
I can get the code to compile by having TranslatableWithSynonymsEntity implement both ITranslatableWithSynonyms<ITranslationWithSynonmys> and ITranslatable<ITranslation>, but that means managing two lists and it doesn't look clean.
internal class TranslatableWithSynonymsEntity : ITranslatableWithSynonyms<ITranslationWithSynonmys>, ITranslatable<ITranslation>
{
public IList<ITranslationWithSynonmys> SynonymTanslations { get; set; }
public IList<ITranslationWithSynonmys> Translations { get; set; }
IList<ITranslation> ITranslatable<ITranslation>.Translations { get; set; }
}
Is there a way to avoid this? Or am I taking a wrong approach?
Thank you
Generic parameters are invariant by default, in the method Translate you want the type to be <ITranslation>, so you must provide a type whose (or its parents') generic parameter is exactly <ITranslation>.
In your example you cannot simply mark the parameter as covariant because it contains a property has both getter and setter.
Since the problem is the generic parameter, to solve the problem, don't specify one, in fact you have already constrained the generic parameter.
interface ITranslatable<T> where T : ITranslation
The method (or the class) just need to be declared with the same constraint.
internal string Translate<T>(ITranslatable<T> translatable, string languageCode)
where T : ITranslation
I have a interface like this:
public interface IMyInterface<T> where T:class
{
long OS { get; set; }
T App { get; set; }
}
and another interface like this:
public interface IMyInterfaces
{
List<IMyInterface<T>> Subscribers { get; set; } //this line give me error
}
I got error
You need to specify a concrete type or another generic parameter for T when you use IMyInterface<T>
public interface IMyInterfaces
{
List<IMyInterface<int>> Subscribers { get; set; }
}
OR
public interface IMyInterfaces<TOther>
{
List<IMyInterface<TOther>> Subscribers { get; set; }
}
Note I used TOther to stress that it is another generic parameter, different from the T in IMyInterface but you could use the same name (T) for TOther
I have the following interface representing a hierarchical data structure hence the name IHierachicalItem
public interface IHierachicalItem
{
IHierachicalItem Parent { get; set; }
IList<IHierachicalItem> Children { get; set; }
}
Now I have multiple classes that inherits from this interface:
public class HierachicalItemA : IHierachicalItem
{
public IHierachicalItem Parent { get; set; }
public IList<IHierachicalItem> Children { get; set; }
}
public class HierachicalItemB : IHierachicalItem
{
public IHierachicalItem Parent { get; set; }
public IList<IHierachicalItem> Children { get; set; }
}
public class HierachicalItemC : IHierachicalItem
{
public IHierachicalItem Parent { get; set; }
public IList<IHierachicalItem> Children { get; set; }
}
I wanted to extend the interface so that the classes return upon accessing its parent and children property the same class instead of the interface. So I thought about using a generic interface:
public interface IHierachicalItem<T> : IHierachicalItem
{
new T Parent { get; set; }
new IList<T> Children { get; set; }
}
Now I am facing the problem that I only want to have one instance of Children and don't call something like .OfType.ToList().
How can I achieve this?
public class HierachicalItemB : IHierachicalItem<HierachicalItemB>
{
IHierachicalItem IHierachicalItem.Parent { get { return this.Parent as IHierachicalItem; } set { this.Parent = (HierachicalItemB)value; } }
IList<IHierachicalItem> IHierachicalItem.Children { get { return this.Children.OfType<IHierachicalItem>().ToList(); } set { this.Children = value.OfType<HierachicalItemB>().ToList(); } }
public HierachicalItemB Parent { get; set; }
public IList<HierachicalItemB> Children { get; set; }
}
I also could have used .Cast<> instead of .OfType<> but this doesn't change the the fact that I would have to call .ToList() or if the Interface would say its an ObersavbleCollection again and again init a new ObservableCollection, any ideas?
You can't. Your IHierachicalItem interface demands a property with the signature IList<IHierachicalItem> Children, while IHierachicalItem<T> demands IList<T> Children. You need both properties implemented. This is the same for your other property.
That is why you need the implicit interface implementation to tell the compiler you comply to both interfaces. There is no way to workaround this, besides of dropping one of the interfaces.
Note: I think you T should be restricted to the IHierachicalItem<T> type:
public interface IHierachicalItem<T> : IHierachicalItem where T : IHierachicalItem
I have the following interface declarations:
interface IOrder<T> where T: IOrderItem
{
IList<T> Items { get; set; }
}
interface IOrderItem
{
IOrder<IOrderItem> Parent { get; set; } // What do I put here?
}
I want the items in the list to have a reference to the header object, so it can use the ID and other fields from the header.
In my concrete classes, it complains that I don't implement "Parent" properly.
class StoreOrder : IOrder<StoreOrderItem>
{
public IList<StoreOrderItem> Items { get; set; }
}
class StoreOrderItem : IOrderItem
{
public StoreOrder Parent { get; set; } // This doesn't satisfy the interface
}
I tried setting up IOrderItem as IOrderItem<T> and passing in the Parent type, but that lead to circular reference since the Header class requries the Item class type... I got confused.
Any advice on how to implement this properly?
If you define your interfaces like so:
interface IOrder<T> where T : IOrderItem<T>
{
IList<T> Items { get; set; }
}
interface IOrderItem<T> where T : IOrderItem<T>
{
IOrder<T> Parent { get; set; }
}
You can then implement them like this to get the functionality that you expect:
class StoreOrder : IOrder<StoreOrderItem>
{
public IList<StoreOrderItem> Items { get; set; }
}
class StoreOrderItem: IOrderItem<StoreOrderItem>
{
public IOrder<StoreOrderItem> Parent { get; set; }
}
class StoreOrder : IOrder<StoreOrderItem>
{
public int Id { get; set; }
}
class StoreOrderItem : IOrderItem
{
public IOrder<IOrderItem> Parent { get; set; } // This doesn't satisfy the interface
}
You may not specialize - IOrder<IOrderItem> is more general than StoreOrder
Here's a solution for changing the interfaces:
interface IOrder<TOrder, TOrderItem>
where TOrderItem : IOrderItem<TOrder>
{
IList<TOrderItem> Items { get; set; }
}
interface IOrderItem<TOrder>
{
TOrder Parent { get; set; }
}
Making changes to StoreOrder and StoreOrderItem to support the interface changes AND adding a couple properties to each for a later test:
class StoreOrder: IOrder<StoreOrder, StoreOrderItem>
{
public DateTime Date { get; set; }
public IList<StoreOrderItem> Items { get; set; }
}
class StoreOrderItem : IOrderItem<StoreOrder>
{
public string ItemName { get; set; }
public decimal ItemPrice { get; set; }
public StoreOrder Parent { get; set; }
}
...and now creating StoreOrder and StoreOrderItem instances, and putting them through their paces:
void Main()
{
var so = new StoreOrder { Date = DateTime.Now };
var item = new StoreOrderItem {
Parent = so,
ItemName = "Hand soap",
ItemPrice = 2.50m };
so.Items = new [] { item };
Console.WriteLine(item.Parent.Date);
Console.WriteLine(so.Items.First().ItemName);
}
...when run, printed:
3/16/2012 10:43:55 AM
Hand soap
Another option is to scrap the above and take this solution and alter it by adding the Parent property with the desired type and using explicit interface implementation to avoid casting at the call-sites, making for a StoreOrderItem implementation something like this:
class StoreOrderItem : IOrderItem
{
public string ItemName { get; set; }
public decimal ItemPrice { get; set; }
public StoreOrder Parent { get; set; } // note: original implementation
IOrder<IOrderItem> IOrderItem.Parent { // explicit interface implementation
get { return (IOrder<IOrderItem>)this.Parent; }
set { this.Parent = (StoreOrder)value; }
}
}
My favorite of the above is the first proposal above with the two-generic parameters to IOrder and the unconstrained generic-parameter on IOrderItem. A previous version I had posted and have now edited had both interfaces each with the same two generic types each with the same constraints. I felt like this was going a bit overboard so I pared it back to the above implementation. Although there is a complete lack of constraints on TOrder type parameter to IOrderItem - attempts to fudge other types in its place (e.g., object) resulted in compile errors. Using TOrder instead of just calling it T provides a hint about the expected type in the absence of the type constraint. That will be my final edit - I feel it is the most succinct of my attempts; if you are curious I can provide the former implementation that had the double-generic-constrained-types on the interfaces, but this is at least my preferred this solution. cheers!
Declaration to satisfy the interfaces:
class StoreOrder : IOrder<StoreOrderItem>
{
// interface members
public IList<StoreOrderItem> Items { get; set; }
// own members
public int Id { get; set; }
}
class StoreOrderItem : IOrderItem
{
public IOrder<IOrderItem> Parent { get; set; }
}
To access custom members you will have to cast:
class StoreOrderItem : IOrderItem
{
void Test()
{
int id = ((StoreOrder)this.Parent).ID;
}
}
I have been reading around but I have not come across a solution to my problem
I am currently working with a Business Object that will hold all my data and we need to convert this object to and from XML.
My object holds a list of Actions (List...), but there are 2 action types (for now).
I have to action types SimpleAction and CompositeAction, and they both inherit from IAction allowing them to both be held in the Actions list.
Now you can probably see the problem as Interfaces cannot be serialized as they hold no data.
How, with maybe some sample code, do I write a Class or Serializer that gets that object type and performs then serializes object with the correct type?
Some code:
[XmlArray("Actions")]
public List<IAction> Actions { get; set; }
public interface IAction
{
int ID { get; set; }
ParameterCollection Parameters { get; set; }
List<SectionEntity> Validation { get; set; }
TestResultEntity Result { get; set; }
string Exception { get; set; }
}
[XmlType("A")]
public class SimpleActionEntity : IAction
{
#region IAction Members
[XmlAttribute("ID")]
public int ID { get; set; }
[XmlIgnore]
public ParameterCollection Parameters { get; set; }
[XmlIgnore]
public List<SectionEntity> Validation { get; set; }
[XmlIgnore]
public TestResultEntity Result { get; set; }
[XmlElement("Exception")]
public string Exception { get; set; }
#endregion
}
Any help would be greatly appreciated. :)
You can use XmlArrayItemAttribute, As we discussed it's no good to create a list of IAction so it's good to create base class
public interface IAction {}
public abstract class ActionBase : IAction {}
public class SimpleAction : ActionBase {}
public class ComplexAction : ActionBase {}
[XmlArray("Actions")]
[XmlArrayItem(typeof(SimpleAction)),XmlArrayItem(typeof(ComplexAction))]
public List<ActionBase> Actions { get; set; }
In fact you also can control Element names in the xml file like this:
[XmlArray("Actions")]
[XmlArrayItem(typeof(SimpleAction),ElementName = "A")]
[XmlArrayItem(typeof(ComplexAction),ElementName = "B")]
public List<ActionBase> Actions { get; set; }
Ok I have created a solution that I feels does what I want pretty well.
What I did is rather than holding
[XmlArray("Actions")]
public List<IAction> Actions { get; set; }
I decided to create an ActionsCollection class that handled the List BUT also allowed me to use IXMLSerializable to override the ReadXml and WriteXML methods so that I could handle the way the list is Serialized and Deserialized.
[XmlElement("Actions")]
public ActionCollection Actions { get; set; }
public class ActionCollection: CollectionBase, IXmlSerializable
{
#region IList Members
...
#endregion
#region ICollection Members
...
#endregion
#region IEnumerable Members
...
#endregion
#region IXmlSerializable Members
public System.Xml.Schema.XmlSchema GetSchema()
{
return null;
}
public void ReadXml(System.Xml.XmlReader reader)
{
//TODO
}
public void WriteXml(System.Xml.XmlWriter writer)
{
foreach (IAction oAction in List)
{
XmlSerializer s = new XmlSerializer(oAction.GetType());
s.Serialize(writer, oAction);
}
}
#endregion
}
Maybe if you derive your two action classes from a common abstract base class that implements the interface?
public interface IAction {}
public abstract class ActionBase : IAction {}
public class SimpleAction : ActionBase {}
public class ComplexAction : ActionBase {}
Then instead of using List<IAction>, use List<ActionBase>.