I have an abstract base class that is defined like this:
public abstract class MyBaseClass<T>
The class contains a definition for the method Get:
protected abstract MyBaseClass<T> Get(T id);
I create MyClass using MyBaseClass:
public class MyClass : MyBaseClass<string>
Now I have to implement Get, but don't know how to define it:
public override MyClass Get(object id)
or
public override MyClass Get(string id)
In both cases I will have to mention string as T and I would like to avoid it.
What is the correct way to override Get ?
Thank You.
When you stated the interface you were implementing you specified the generic argument as string when you wrote (: MyBaseClass<string>), as such the only way for you to implement the Get method is to use string in place of all values for T. If you want users of your class to be able to use other types then you need to make the implementing class generic as well:
public class MyClass<T> : MyBaseClass<T>
{
protected override MyBaseClass<T> Get(T id)
{
throw new NotImplementedException();
}
}
public abstract class MyBaseClass<T>
{
protected abstract MyBaseClass<T> Get(T id);
}
public class MyClass : MyBaseClass<string>
{
protected override MyBaseClass<string> Get(string id)
{
return FindById(id);//implement your logic
}
}
Implement abstaract class as follows:
public abstract class MyBaseClass<T>
{
protected abstract MyBaseClass<T> Get(T id);
protected abstract MyBaseClass<T> Get(string id);
}
And the extending class:
class Class1 : MyBaseClass<Object>
{
protected override MyBaseClass<object> Get(object id)
{
return (MyBaseClass<object>) id;
}
protected override MyBaseClass<object> Get(string id)
{
return FindMyBaseClass(id)
}
}
Related
Hi i'm trying to implement a structure where by I need to be able to create an abstract method in an abstract class in C#, which has an abstract object as a parameter.. example-
public abstract class AbstractMapper
{
protected abstract AbstractObject doLoad(AbstractObject obj);
}
public abstract class UserMapper
{
protected override User doLoad(User obj)
{
}
}
In this example the "User" class extends the "AbstractObject" class... This is giving me errors on compile. Can someone advise on how i should achieve the above?
Use a generic type parameter on AbstractMapper constrained to be a subtype of AbstractObject:
public abstract class AbstractMapper<T> where T : AbstractObject
{
protected abstract T doLoad(T obj);
}
public class UserMapper : AbstractMapper<User>
{
protected override User doLoad(User obj)
{
...
}
}
UserMapper is extending Object class and you are trying to override a method that doens't exist (doLoad).
Also, the signature of the method has a return type of User and you are not returning anything.
If you want User class to extend AbstractObject class, then do this:
public class User : AbstractObject
{
protected AbstractObject doLoad(AbstractObject obj)
{
// do something here and return an instance of a class that extends Abstract object
return null; // added to make it compile
}
}
Do you know that the access modifier protected means that it is only visible inside the class and in child classes? Read this: https://msdn.microsoft.com/en-us/library/wxh6fsc7.aspx
this may be somewhere else under generic types but I cant seem to follow a lot of the answers. Apologies if this is a repeat of another question.
the following code is for a three layer app with Data, Logic and Presentation Layers
in my data layer I have a Collection of entitys and a base entity
public abstract class BaseEntity
{
int LastModifiedBy { get; set; }
DateTime LastModifiedDate{get;set;}
}
public partial class DocNum: BaseEntity
{
}
public partial class DataList: BaseEntity
{
}
in my logic layer I have a BaseDTO class for transferring data. here is the code for it
public abstract class BaseDTO
{
protected abstract void ConvertFromEntity(BaseEntity entity);
public abstract void ConvertToEntity();
}
I then go and create the implementation class DocNum based on it as follows
public class DTODocNum : BaseDTO
{
//properties here
public DTODocNum()
{
}
public DTODocNum(DocNum entity)
{
ConvertFromEntity(entity)
}
protected override void ConvertFromEntity(DocNum entity)
{
throw new NotImplementedException();
}
public override void ConvertToEntity()
{
throw new NotImplementedException();
}
}
however this will not compile telling me that no suitable method to override was found.
I know I can do the following but I want thhis method to only accept a DocNum entity from the Data Layer:
protected override void ConvertFromEntity(BaseEntity entity)
{
throw new NotImplementedException();
}
I have also tried generic types with the following
public abstract class BaseDTO
{
protected abstract void ConvertFromEntity<T>(T entity);
public abstract T ConvertToEntity<T>();
}
and the following in the derived class:
protected override void ConvertFromEntity<T>(T entity) where T:DocNum
{
throw new NotImplementedException();
}
but now the error given is Constraints for override and explicit interface implementation methods are inherited from the base method, so they cannot be specified directly
Can any one help me implement this solution so that the DTODocNum can compile whilst referring to the entity type?
Move the type parameter to the class level and add a constraint:
public abstract class BaseDTO<T> where T : BaseEntity
{
protected abstract void ConvertFromEntity(T entity);
public abstract T ConvertToEntity();
}
public class DTODocNum : BaseDTO<DocNum> { ... }
I have a base class that has some abstract methods on it and there are 21 classes that are inheriting from this base class. Now for one of those abstract methods I want to implement it with a common implementation for 6 of the 21 classes so I thought about creating another base class that would do this.
I am open to suggestions but my main purpose of creating another base class between the current base class and the 21 classes is to keep from repeating the same code in 6 of the 21 classes if I didn't have to.
Here is a sample of code to illustrate the situation:
public abstract class FooBase
{
public abstract string Bar();
public abstract string SomeMethod();
public virtual string OtherMethod()
{
return this.SomeMethod();
}
}
public abstract class AnotherBase : FooBase
{
public abstract string Bar();
public abstract string SomeMethod();
public override OtherMethod()
{
//this is the common method used by 6 of the classes
return "special string for the 6 classes";
}
}
public class Foo1 : FooBase
{
public override string Bar()
{
//do something specific for the Foo1 class here
return "Foo1 special string";
}
public override string SomeMethod()
{
//do something specific for the Foo1 class here
return "Foo1 special string";
}
}
public class Another2 : AnotherBase
{
public override string Bar()
{
//do something specific for the Another2 class here
return "Another special string";
}
public override string SomeMethod()
{
//do something specific for the Another2 class here
return "Another2 special string";
}
}
Yes, you can derive an abstract class from another abstract class
public abstract class FooBase
{
//Base class content
}
public abstract class AnotherBase : FooBase
{
//it is "optional" to make the definition of the abstract methods of the Parent class in here
}
When we say it is optional to define the abstract methods of the parent class inside of the child class, it is mandatory that the child class should be abstract.
public abstract class FooBase
{
public abstract string Bar();
public abstract string SomeMethod();
public abstract string OtherMethod();
}
public abstract class AnotherBase : FooBase
{
public override string OtherMethod()
{
//common method that you wanted to use for 6 of your classes
return "special string for the 6 classes";
}
}
//child class that inherits FooBase where none of the method is defined
public class Foo1 : FooBase
{
public override string Bar()
{
//definition
}
public override string SomeMethod()
{
//definition
}
public override string OtherMethod()
{
//definition
}
}
//child class that inherits AnotheBase that defines OtherMethod
public class Another2 : AnotherBase
{
public override string Bar()
{
//definition
}
public override string SomeMethod()
{
//definition
}
}
So I'm guessing that there will be 5 more classes like Another2 which inherits from AnotherBase that will have a common definition for OtherMethod
Yes, that is entirely possible and frequently done. There is no rule that says that you can have only one base class at the bottommost level of your class hierarchy; subclasses of that class can just as well be abstract and thereby become (somewhat more specialized) base classes for one group of classes indirectly derived from your general base class.
You should specify what exactly those classes do, but.. given the information you provided:
This is the exact problem that the Strategy pattern aims to solve, as shown in the example given in the Head First Design Patterns book.
You have an abstract Duck class, from which other ducks (e.g., RedheadDuck, MallardDuck) derive. The Duck class has a Quack method, that simply displays the string "quack" on the screen.
Now you are told to add a RubberDuck. This guy doesn't quack! So what do you do? Make Quack abstract and let the subclasses decide how to implement this? No, that'll lead to duplicated code.
Instead, you define an IQuackBehaviour interface with a Quack method. From there, you derive two classes, QuackBehaviour and SqueakBehaviour.
public class SqueakBehaviour: IQuackBehaviour
{
public void Quack(){
Console.WriteLine("squeak");
}
}
public class QuackBehaviour: IQuackBehaviour
{
public void Quack(){
Console.WriteLine("quack");
}
}
Now, you compose your ducks with this behaviour as appropriate:
public class MallardDuck : Duck
{
private IQuackBehaviour quackBehaviour = new QuackBehaviour();
public override void Quack()
{
quackBehaviour.Quack();
}
}
public class RubberDuck : Duck
{
private IQuackBehaviour quackBehaviour = new SqueakBehaviour();
public override void Quack()
{
quackBehaviour.Quack();
}
}
You can even inject an instance of IQuackBehaviour through a property if you want the ducks to change their behaviour at runtime.
I'm trying to implement a factory pattern and I ran into a problem. I try to make my classes simple here. Basically I have a base Packet class (PacketHeader) with some fields and methods. Also I have so many derived packet classes such as: InfoPacket1011, UsagePacket1011, InfoPacket1014, UsagePacket1014 and they all inherit from PacketHeader base class.
As you can see each packet has a version and my goal is to handle this packets based on their versions. So I should have two derived class, one for 1011 and one for 1014.
The base class (which itself is a derived class!) looks like this:
public abstract class PacketHandlerBase : Engine
{
public abstract bool SendInfoPacket(int someInt, string someInput);
public abstract List<???> BuildInfoPacket(string someInput);
public abstract bool SendUsagePacket(int someInt, string someInput);
public abstract List<???> BuildUsagePacket(string someInput);
//...
//...
//...
}
My problem is that for methods such as BuildInfoPacket and BuildUsagePacket I have to return a List of that type. So in the derived classes I could have:
public class PacketHandler1011 : PackerHandlerBase
{
//...
public override bool SendInfoPacket(int someInt, string someInput);
{
// code implementation
// return true or false
}
public override List<InfoPacket1011> BuildInfoPacket(string someInput);
{
// code implementation
// return List<InfoPacket1011>
}
}
public class PacketHandler1014 : PackerHandlerBase
{
//...
public override bool SendInfoPacket(int someInt, string someInput);
{
// code implementation
// return true or false
}
public override List<InfoPacket1014> BuildInfoPacket(string someInput);
{
// code implementation
// return List<InfoPacket1014>
}
}
I don't know what to use in the PacketHandlerBase class to be able to override it in the derived classes. I guess I need generic methods and interface for that, but not sure how to handle that.
[Edit]: I fixed first part of my questions about packet inheritance. Thank you all for your answers, I read them and tell you if they work.
[Answer]: Thank you everyone for your prompt responses. I fixed the problem by passing List and by casting it in the method and in the caller. Well my code was much more complex than what I provided here and I just finished modifying it. I changed the pattern to abstract factory too to fix some other problems.
Any help would be greatly appreciated.
Thanks in advance
You are implementing in fact an Abstract Factory pattern where PackerHandlerBase is an Abstract Factory and it produces/builds an Abstract Product which in your case is an InfoPacket and UsagePacket. Concrete Factory is PacketHandler1011 or PacketHandler1014. And Concrete Product is InfoPacket1011 or InfoPacket1014 and so on.
So it should be:
public abstract class PacketHandlerBase : Engine
{
public abstract bool SendInfoPacket(int someInt, string someInput);
public abstract List<InfoPacket> BuildInfoPacket(string someInput);
public abstract bool SendUsagePacket(int someInt, string someInput);
public abstract List<UsagePacker> BuildUsagePacket(string someInput);
//...
}
public class InfoPacket1014 : InfoPacket
{
///...
}
public class PacketHandler1011 : PackerHandlerBase
{
//...
public override List<InfoPacket> BuildInfoPacket(string someInput);
{
// code implementation
return new List<InfoPacket> { new InfoPacket1011(), ... };
}
}
all your method in the base class should return InfoPacketBase as well as creating a base class for packet usage e.g UsagePacketBase you need to take a look at polymorphism
public abstract class PacketHandlerBase : Engine
{
public abstract bool SendInfoPacket(int someInt, string someInput);
public abstract List<PackeHeader> BuildInfoPacket(string someInput);
public abstract bool SendUsagePacket(int someInt, string someInput);
public abstract List<PackeHeader> BuildUsagePacket(string someInput);
//...
//...
//...
}
Here is an example to use it generic way:
Use your entities in type constraint like:
where T : InfoPacketBase and in derived class method: List<InfoPacket1011>;
abstract class A
{
public abstract List<T> BuildInfoPacket<T>(string someInput) where T : new();
}
class B : A
{
public override List<T> BuildInfoPacket<T>(string someInput)
{
// code implementation
return new List<T> { new T() };
}
public void Test()
{
BuildInfoPacket<object>("test");
}
}
Do not use generics if you don't understand them and are fully aware of their downsides. In this case, you can just return IEnumerable<PacketHeader> and have the polymorphism resolve rest.
public abstract class PacketHandlerBase : Engine
{
public abstract bool SendInfoPacket(int someInt, string someInput);
public abstract IEnumerable<PacketHeader> BuildInfoPacket(string someInput);
public abstract bool SendUsagePacket(int someInt, string someInput);
public abstract IEnumerable<PacketHeader> BuildUsagePacket(string someInput);
//...
//...
//...
}
public class PacketHandler1011 : PackerHandlerBase
{
//...
public override bool SendInfoPacket(int someInt, string someInput);
{
// code implementation
// return true or false
}
public override IEnumerable<PacketHeader> BuildInfoPacket(string someInput);
{
yield return new InfoPacket1011(..)
// code implementation
// return List<InfoPacket1011>
}
}
How about:
public abstract class PacketHandlerBase<TInfoPacket, TUsagePacket> : Engine
where TInfoPacket : IInfoPacket
where TUsagePacket : IUsagePacket
{
public abstract bool SendInfoPacket(int someInt, string someInput);
public abstract List<TInfoPacket> BuildInfoPacket(string someInput);
public abstract bool SendUsagePacket(int someInt, string someInput);
public abstract List<TUsagePacket > BuildUsagePacket(string someInput);
}
You make sure that your info packet classes implement an IInfoPacket interface. For example:
public InfoPacket1101 : PacketHeader, IInfoPacket
{
...
}
Similarly all the usage packet classes implement IUsagePacket. Then you can write a given version of your packet handler like so:
public class PacketHandler1011 : PackerHandlerBase<InfoPacket1101, UsagePacket1101>
{
...
}
I think this is the preferred solution, as it means you can have stronger guarantees about the returned objects. With only a single base class, as in the currently accepted answer, you can't call any "info packet"-specific methods on objects returned by BuildInfoPacket without casting. Similarly with usage packets. In this solution the IInfoPacket interface could have methods that you are then able to call without casting.
I'd like to create an abstract class in c#, that "inherits" from different interfaces, but leaves the concrete implementation to the subclass. The compiler however complains, that the class doesnt implement the methods specified in the interfaces. I'm used to Java where this always worked, so I'm not sure how it is supposed to work in c#. Anyway, this is my code:
public abstract class MyClass : IDisposable, IPartImportsSatisfiedNotification
{
private string name;
public MyClass(string name)
{
this.name = name;
}
}
Add abstract methods:
public interface IPartImportsSatisfiedNotification
{
void SomeMethod();
}
public abstract class MyClass : IDisposable, IPartImportsSatisfiedNotification
{
private string name;
public MyClass(string name)
{
this.name = name;
}
public abstract void SomeMethod();
public abstract void Dispose();
}
public class SubClass : MyClass
{
public SubClass(string someString) : base(someString)
{
}
public override void SomeMethod()
{
throw new NotImplementedException();
}
public override void Dispose()
{
throw new NotImplementedException();
}
}
This is the right way to do it.
public abstract class MyClass : IDisposable, IPartImportsSatisfiedNotification
{
private string name;
public MyClass(string name)
{
this.name = name;
}
public abstract void Dispose();
}
I dont know the definition of your IPartImportsSatisfiedNotification interface so i my sample can only provide the methods defined in IDisposable... Do it for IPartImportsSatisfiedNotification the same way.
You will need to add abstract methods that "implement" those interfaces.
So for instance:
public abstract void Dispose(); // implements IDisposable
You can just declare the methods and properties the interfaces expect as abstract in your abstract class. This forces the subclasses to still do the implementation but doesn't violate C#'s rules of interfaces.
abstract class in basics its a normal class so he also has to implements these methods.
if you want further implementations , put the virtual methods ( or abstract) in the abstract class itself
As noted by others, you would need to mark the methods as abstract in your base class, which will force derived classes to implement. You can run this as a C# program in LinqPad
void Main()
{
DerivedClass dc = new DerivedClass("hello, world");
Console.Out.WriteLine(dc);
string result = dc.Notify("greetings");
Console.Out.WriteLine(result);
}
public interface IPartImportsSatisfiedNotification
{
string Notify(string msg);
}
public abstract class MyClass : IPartImportsSatisfiedNotification
{
protected string name;
public MyClass(string name)
{
this.name = name;
}
abstract public string Notify(string msg);
}
public class DerivedClass : MyClass
{
public DerivedClass(string name) :base(name)
{
}
public override string Notify(string msg)
{
return string.Format("Msg {0} from {1}", msg, this.name);
}
public override string ToString()
{
return this.name;
}
}
you need to add abstract method in your abstract class.
public abstract class MyClass : IDisposable, IPartImportsSatisfiedNotification
{
private string name;
public MyClass(string name)
{
this.name = name;
}
public abstract void dispose();
public abstract void OnImportsSatisfied();
}