Is it possible in C# to implement an Interface through a class member without explicitly returning the members implementation?
I want something like this
interface IAttachement
{
byte[] Data { get; }
string Name { get; }
long Size { get; }
}
class Attachement : IAttachement
{
public byte[] Data { get; set; }
public string Name { get; set; }
public long Size { get; set; }
}
class Request : IAttachement
{
public Attachement Attachement { get; set; } : IAttachement
}
Instead of
class Request : IAttachement
{
public Attachement Attachement { get; set; }
public byte[] Data => Attachement.Data;
public string Name => Attachement.Name;
public long Size => Attachement.Size;
}
No, this isn't a feature that C# offers.
You can delegate interface implementation to a field/property/member, but you have to do it explicitly, as in your example.
If you would like this feature adding to the language, you can raise an issue here.
It is not possible to implement an interface through a class member without explicitly returning the member's implementation. In order for a class to implement an interface, it must provide an implementation for all members of the interface, either explicitly or implicitly. In your example the Request class needs to provide an implementation for the Data, Name, and Size properties of the IAttachment interface, either by implementing them directly or by delegating to the Attachement member.
Related
While implementing an interface, why can't we have concrete implementation of base interface in aggregation?
Which OOP, principle is violating here? StorageEntitySas is essentially of type IStorageEntitySas
public interface IValetKeyResponse
{
IStorageEntitySas Sas { get; set; }
string UploadUrl { get; set; }
}
public class ValetKeyResponse : IValetKeyResponse
{
//Which OOP, principle is violating here? StorageEntitySas is essentially of type IStorageEntitySas
**public StorageEntitySas Sas { get; set; }**
public string UploadUrl { get; set; }
}
public class StorageEntitySas : IStorageEntitySas
{
public string Credentials { get; set; }
public Uri BlobUri { get; set; }
public string Name { get; set; }
}
An interface defines a contract that every implementing class has to fulfill. It defines what a method has to return and which parameters you may use. In particular, users of your interface don't know - and don't have to know anything of the concrete classes, which is an implementation detail.
However you're still able to do the following:
public class ValetKeyResponse : IValetKeyResponse
{
public IStorageEntitySas Sas { get; set; } = new StorageEntitySas();
public string UploadUrl { get; set; }
}
So why is this not allowed? Imagine you have an API that simply returns the interface-type.
IValetKeyResponse response = myClass.GetValetResponse();
// what am I allowed to pass here when I don´t know the actual class of response?
response.Sas = ...
A client of this API doesn´t know which class you actually get and thus which kind of IStorageEntitySaS you´re allowed to assign to that instance. That´s what the contract defines, it sais you can pass anything that implements IStorageEntitySas.
The setter on the Sas property allows you to provide any implementation of IStorageEntitySas. This means you should be able to do:
public class OtherStorageSas : IStorageEntitySas { ... }
IValetKeyResponse r = new ValetKeyResponse();
r.Sas = new OtherStorageSas();
This would not be type-safe if allowed since ValetKeyResponse.Sas has an incompatible type StorageEntitySas.
I have an interface
public interface IIdentity<T>
{
T GetUser();
}
I have a base class that implements the Interface as an abstract method
public abstract class BaseUser<T> : IIdentity<T>
{
public string UserId { get; set; }
public string AuthType { get; set; }
public List<Claim> Claims { get; set; }
public abstract T GetUser();
}
In the class that inherits the base class
public class JwtUser : BaseUser
{
public string Sub { get; set; }
}
I get an error using the generic type BaseUser requires 1 argument, what do i do here, basically I'd like my user to inherit shared properties from the base class which it does (i think) and to implement the generic method from the base class as I'm going to have different types of users (JWT/Windows etc) I need to abstract away the getUsers method, hope that makes sense ?
You have to ways to implement this, both require to set the generic in BaseUser.
You could expose that generic:
public class JwtUser<T> : BaseUser<T>
{
public string Sub { get; set; }
}
Or, just set the generic:
public class JwtUser : BaseUser<JwtUser>
{
public string Sub { get; set; }
}
it should be like , for Ref : Generic Classes (C# Programming Guide)
public class JwtUser<User> : BaseUser<User>
{
public string Sub { get; set; }
}
or
public class JwtUser<T> : BaseUser<T>
{
public string Sub { get; set; }
}
and when create instace
var jwtUser =new JwtUser<User> ();
or
class JwtUser: BaseUser<JwtUser> { }
In all way at the end you must need to specify value for T template as its generic.
For example if you take List<T> for using it you must need to intialize with proper type like if interger list then List<int> intlist = new List<int>();
I have the following two classes:
abstract class LogItem {
public String payload { get; set; }
public String serverId { get; set; }
public DateTime timeRecieved { get; set; }
}
class MyLogItem : LogItem
{
//No I want this to have to have the members from the abstract class above, as if it where an interface?
}
So in other words I am wanting a type if interface that can have definitions or variables which all classes that implement it have to have, but they could add more if they required ?
The above example builds, even if i dono add the members from the abstract class.
edit
Forget what I've said before. These are attributes, not methods. For them to be accessible on derived classes, you make them protected or public. The difference is that public members are visible to the world, while protected ones are visible to the class and subclasses.
Any class derived from your LogItem may have other variables.
abstract class LogItem {
public String payload { get; set; }
public String serverId { get; set; }
public DateTime timeRecieved { get; set; }
}
class MyLogItem : LogItem
{
//No I want this to have to have the members from the abstract class above, as if it where an interface?
private void TestMethod(){
String test = payload;
}
}
check out this post for more information
Your MyLogItem class can reference any of the above members directly. They are accessible
You may declare an interface with those
public interface MyInterface {
public String payload { get; set; }
public String serverId { get; set; }
public DateTime timeRecieved { get; set; }
}
and your class
public class MyLogItem : MyInterface
{
String _payload;
public String payload { get{ return _payload; } set {_payload=value;} }
...
}
The abstract keyword can also be applied to methods, as described here.
i have two data classes which hold only data members(no functions). One is CallTask the other is SmsTask. These two classes have some common properties like ID, Tel. I put these common properties in a seperate interface class and i use this interface class in my project whenever appropriate.
Now i added a WCFService to my project to share data between clients and server. Consider the following class design:
public interface IGsmTask : IComparable
{
string TaskID { get; set; }
string SessionID { get; set; }
string Tel { get; set; }
}
class CallTask : IGsmTask
{
#region IGsmTask Members
public string TaskID { get; set; }
public string SessionID { get; set; }
public string Tel { get; set; }
#endregion
}
class SmsTask : IGsmTask
{
#region IGsmTask Members
public string TaskID { get; set; }
public string SessionID { get; set; }
public string Tel { get; set; }
#endregion
public string SmsText { get; set; }
}
in this design, i want to host CallTask, SmsTask, and IGsmTask to the clients to use these in service methots like the following;
[OperationContract]
public void AddTask(IGsmTask task)
{
}
i tried to mark [DataContract] on IGsmTask but it gives me complition error. Isnt there any methot that i can use interfaces as DataContracts? Or how should i use KnownAttributes types in this synerio?
Thanks.
As far as I know using interfaces as datacontracts is not possible. You may use a base class and add knowntype attributes on the otherhand.
Fer: Everything is Possible with the right design.
If the issue is:
a class is a data contract
&&
1 or more of its properties must be an interface...
public interface ICustomInterface
{
int Property1 {get;set}
}
[DataContract]
public class MyClass
{
[DataMember(Name="_myInterface")]
public ICustomInterface MyInterface {get;set;}
}
The issue is that when the de-serialization occurs --
There is no way to turn the data into a class that implements ICustomInterface.
The Solution is to create a concrete class that does Implement the interface, and cast the getter/setter of the public property (that is of type interface) into a private property of the concrete class.
public class CustomInterfaceImplementor: ICustomInterface
{
public int Property1 {get;set;}
}
[DataContract]
public class MyClass
{
[DataMember(Name="_myInterface")]
private CustomInterfaceImplementor _MyInterface;
public ICustomInterface MyInterface
{
get {return (_MyInterface as ICustomInterface);}
set {_MyInterface = (value as CustomInterfaceImplementor);}
}
}
I have a set of interfaces which are used in close conjunction with particular mutable object.
Many users of the object only need the ability to read values from the object, and then only a few properties. To avoid namespace pollution (easier intellisense) and to get across the usage intent, I'd like to have a small base interface which only exposes a few "key" properties in a read-only fashion.
However, almost all implementations will support the full interface, which includes modifiability.
Unfortunately, I ran into a roadblock expressing that concept in C#:
interface IBasicProps {
public int Priority { get; }
public string Name {get;}
//... whatever
}
interface IBasicPropsWriteable:IBasicProps {
public int Priority { set; } //warning CS0108: [...] hides inherited member [...]
public string Name { set; }
//... whatever
}
I certainly wasn't intending to hide any members, so that aint good!
Of course, I can solve this using methods just fine, but what's the right choice? I'd like to keep the "core" interface as small as possible even if splitting the interfaces serves no purpose other than communicating intent. With split interfaces, it's just really obvious which methods aren't going to do any updating, and it makes writing code a bit clearer (not to mention also allows nice-n-simple static singleton stubs that suffice for quite a few simple cases).
I'd like to avoid any abstract classes and the like; they make reimplementation or quick single-purpose shims all that more complex and hard-to-grok.
So, ideas?
Method hiding in an interface isn't nearly as grungy; I'd go with something like:
interface IBasicProps {
int Priority { get; }
string Name {get;}
//... whatever
}
interface IBasicPropsWriteable:IBasicProps {
new int Priority { get; set; }
new string Name { get; set; }
//... whatever
}
class Foo : IBasicPropsWriteable {
public int Priority {get;set;}
public string Name {get;set;}
/* optional
int IBasicProps.Priority {get {return Priority;}}
string IBasicProps.Name {get {return Name;}}
*/
}
If your goal is to make it clearer when reading vs. writing is allowed, then I would use separate getter and setter methods rather than properties.
interface IBasicProps {
int GetPriority();
string GetName();
//... whatever
}
interface IBasicPropsWriteable:IBasicProps {
void SetPriority(int priority);
void SetName(string name);
//... whatever
}
One way could be to simply skip the inheritance of the interfaces. Make one read-only interface and one write-only, and implement as necessary:
interface IBasicPropsReadable {
int Priority { get; }
string Name { get; }
}
interface IBasicPropsWriteable {
int Priority { set; }
string Name { set; }
}
class SomeClassReadWrite : IBasicPropsReadable, IBasicPropsWriteable {
int Priority { get; set; }
string Name { get; set; }
}
class SomeClassReadOnly : IBasicPropsReadable {
int Priority { get; }
string Name { get; }
}
You could leave the interfaces unrelated and simply have your class implement both interfaces. After all the interfaces are simply defining the contract and the contracts don't need to be related. It seems like it just an optimization for you when coding to have the writeable one derive from the other, so you only have to specify one interface.
public interface IBasicProps
{
int Priority { get; }
string Name {get;}
//... whatever
}
public interface IBasicPropsWriteable
{
int Priority { get; set; }
string Name { get; set; }
//... whatever
}
public class Foo : IBasicProps, IBasicPropsWriteable
{
public int Priority { get; set; }
public string Name { get; set; }
// whatever
}
If you really needed the optimization, you could create another interface that derives from both and have your classes implement that.
public interface IBasicPropsAll : IBasicProps, IBasicPropsWriteable { }
public class Foo : IBasicPropsAll
{
public int Priority { get; set; }
public string Name { get; set; }
// whatever
}