I have 2 classes that are both derived from a base class X. The base class contains a property of a class T. Both subclasses of X should contain a property that's derived from T.
What I would like to achieve is to declare the a property of T in the base class X and have it used in several methods, while using the same property of T in the derived classes of X but have it recognized as a derived class from T, so that I won't have to cast it every time I want to use it.
One of my solutions would be just remove the property from the base class and copy the methods for each derived class of X, but that would defeat the purpose of using inheritance.
Is anything like that achievable?
internal class TestObject
{
public string ID;
public XObject obj;
//....
}
internal class TestDocument : TestObject
{
public XDocument obj; //<--- want to be able to call obj in my methods
//as if it were an XDocument type but relate to the obj property in the base class
//....
}
internal class XObject
{
//....
}
internal class XDocument : XObject
{
//....
}
Generics should work for you:
class Base<T> where T: MyType
{
T MyProperty { get; set; }
public void DoSomething()
{
// do something with MyProperty
}
}
with MyType being the base-class of the property within Base.
Then in your derived class you can define the generic constraint, e.g.
class Derived : Base<DerivedType>
{
}
Now an instance of Derived has the property MyProperty of type DerivedType instead of MyType.
So in your case TestObject should be similar to this:
internal class TestObject<T> where T: XObject
{
public string ID;
public T obj;
//....
}
internal class TestDocument : TestObject<XDocument>
{
// obj is here of type XDocument
}
Make the type of the property a generic parameter of your base class:
class PropertyTypeBase { }
class PropertyTypeA : PropertyTypeBase { }
class Base<T> where T : PropertyTypeBase
{
public T Property { get; }
}
class Foo : Base<PropertyTypeA>
{
public Foo()
{
PropertyTypeBase x = Property;
PropertyTypeA a = Property;
}
}
The simplest way would be to make the base class generic, and constrain the generic parameter to be derived form a certain class:
class BaseProp { }
class DerivedPropA: BaseProp { }
class DerivedPropB : BaseProp { }
abstract class X<T>
where T: BaseProp
{
public T Value { get; set; }
public abstract void With(T value);
}
class A : X<DerivedPropA>
{
public override void With(DerivedPropA value)
{
this.Value = value;
}
}
class B : X<DerivedPropB>
{
public override void With(DerivedPropB value)
{
this.Value = value;
}
}
This is possible by using generics.
First, let me explain the example classes. Let's say these are your properties:
public class BaseHead {}
public class OrganicHead : BaseHead {}
public class CyborgHead : BaseHead {}
And you now want to implement these heads on your person classes:
public class BaseCreature {}
public class OrganicCreature : BaseCreature {}
public class CyborgCreature : BaseCreature {}
The solution:
public class BaseCreature<THead> where THead : BaseHead
{
public THead Head { get; set; }
public BaseCreature(THead head)
{
this.Head = head;
}
}
We make the BaseCreature generic
We limit the THead type to only allow types that either are BaseHead or are derived from BaseHead
However, we also want to ensure that the right creature (organic/cyborg) only uses the correct head (organic/cyborg). This can be done by deriving from a BaseCreature with a specific generic type:
public class OrganicCreature : BaseCreature<OrganicHead>
{
public OrganicCreature(OrganicHead head) : base(head)
{
}
}
CyborgCreature is analogous.
Suppose you wanted to make it possible that every creature can use every type of head. If that's what you want, then you need to keep the generic parameter generic:
public class OrganicCreature<THead> : BaseCreature<THead> where THead : BaseHead
{
public OrganicCreature(THead head) : base(head)
{
}
}
CyborgCreature is analogous.
Related
Suppose a class defined as below,
public class MyGeneric<T> where T : MyGeneric<T>
{
}
Can we create an object of this class? If not, why does this exist?
I'm asking this of my curiosity and don't have an in depth knowledge in C#.
It's useful when you have a class hierarchy, and you want to be able to write methods in the base class which return instances of the derived class (such as this):
public abstract class Base<T> where T : Base<T>
{
public T WithFoo(int foo)
{
// ...
return (T)this;
}
}
public class Derived : Base<Derived>
{
// ...
}
Derived d = new Derived().WithFoo(3);
Of course, this doesn't stop someone from writing:
public class Other : Base<Derived> { }
... and the only way to get around this is with a runtime check, which can be ugly:
public Base()
{
Trace.Assert(typeof(T) == this.GetType());
}
Some other languages have specific keywords to cover this case.
You can do it by inheriting from MyGeneric:
public class MyGeneric<T> where T : MyGeneric<T>
{
}
class MyGenericChild : MyGeneric<MyGenericChild>
{
}
var myGenericChild = new MyGenericChild();
var myGeneric = new MyGeneric<MyGenericChild>();
This is helpful when there is need to create type-specific members in the base class, specific to the actual descendant.
public class MyGeneric<T> where T : MyGeneric<T>
{
public void Do(T t)
{
...
}
}
class MyGenericChild : MyGeneric<MyGenericChild>
{
// Do for MyGenericChild will accept only MyGenericChild and it's descendants
}
I have 2 APIs which both have the same methods but with different names.
I made an abstract class inherited from this with both of them.
Now I am trying to make another class which uses those APIs and I don't want it to care which API it uses.
How do I pass the abstract class as a parameter and use it as one of the api's?
Is there a better way to do it?
Example Code :
public abstract class AbstractClass
{
public abstract string Func1();
}
public class Class1: AbstractClass
{
public override string Func1()
{
return "Class1";
}
}
public abstract class Class2: AbstractClass
{
public override string Func1()
{
return "Class2";
}
}
public class Class3
{
Type type;
public Class3(Type type)
{
this.type = type;
}
public string UseFunc1()
{
//I know this wont work but what shuld I do
type a = new type();
return a.Func1();
}
}
I think what you might be trying to achieve is the below. While you can't create an abstract class you can pass one
public class Class3
{
AbstractClass abstractMember
public Class3(AbstractClass abstractMember)
{
this.abstractMember = abstractMember;
}
public string UseFunc1()
{
return abstractMember.Func1();
}
}
You'd call it like:
Class2 c2 = new Class2();
Class3 c3 = new Class3(c2);
I have the following base class
class BaseClass
{
//Want to get the name of class A only, even if B is inherited from A
}
class A : BaseClass
{
}
class B : A
{
}
Can someone help me with getting the name of class A only from the base class.
Thanks
public abstract class BaseClass
{
public void GetInheritorName()
{
var nameIs = this.InheritorTellMeYourName();
}
protected abstract string InheritorTellMeYourName();
}
public class A : BaseClass
{
protected sealed override string InheritorTellMeYourName()
{
return typeof(A).Name;
}
}
public class B : A
{
}
Like someone mentioned in the comments, you shouldn't usually need anything like that...
I've a generic base class where generic type is class and other related inherited class:
public class BaseClass<T> where T : class
{
virtual void DoWork(){..}
virtual void DoAnotherWork(){..}
}
public class SomeInherit<Person> : BaseClass<Person>
{
//...
}
public class OtherInherit<Car> : BaseClass<Car>
{
// override something..
}
Then, I've a BaseClassManager which should be able to load some BaseClass inherited by some co-worker via reflection:
public class BaseClassManager
{
public BaseClass<TItem> LoadBaseClass<T>() where T : BaseClass<???>
{
// how can create an instance of T?
// TItem : class
// T : BaseClass
// -------------> in reality, it should be: T<TItem> (just as BaseClass<Person>)
}
}
Is there any way to accomplish that..?
You need to define a second type parameter for where T : BaseClass<???>.
You can use the new() constraint to allow the method to create instances of a generic type.
public TBaseClass LoadBaseClass<TBaseClass, TItem>()
where TBaseClass : BaseClass<TItem>, new()
where TItem : class
{
return new TBaseClass();
}
Usage:
SomeInherit<Foo> result = LoadBaseClass<SomeInherit<Foo>, Foo>();
I need a method that creates an empty clone of an object in a base class? For instance:
public class ChildClass : ParentClass
{
public ChildClass()
{
}
}
public class ParentClass
{
public SomeMethod()
{
// I want to create an instance of the ChildClass here
}
}
Up until now, we have an abstract method defined in the parent class. And, all of the child classes implement them. But, the implementation is the same for all, just a different type.
public class ChildClass : ParentClass
{
public ChildClass()
{
}
public ParentClass CreateEmpty()
{
return new ChildClass();
}
}
public class ParentClass
{
public SomeMethod()
{
// I want to create an instance of the ChildClass here
ParentClass empty = CreateEmpty();
}
public abstract ParentClass CreateEmpty();
}
Is there any way to do this from the parent class so that I don't have to keep implementing the same logic for each different child class? Note that there may be more levels of inheritance (i.e. ChildChildClass : ChildClass : ParentClass).
If using reflection isn't a problem to you, you could do it using Activator class:
//In parent class
public ParentClass CreateEmpty()
{
return (ParentClass)Activator.CreateInstance(this.GetType());
}
This will return empty object of the type you want. Notice that this method does not need to be virtual.
On the other hand, I think that your current approach is perfectly fine, few more lines of code aren't so bad.
You can make a deep clone of the object using the binary serializer.
EDIT: Just noticed the word "empty" next to clone (which I thought was an oxymoron). Leaving this response up anyhow hoping it will help others that find this question because they are looking to do a regular clone.
This is somewhat experimental. I don't know whether this will lead to a cyclic dependency. Haven't touched C# for some months.
public class ParentClass<T> where T : ParentClass<T>, new() { // fixed
public ParentClass() {
var x = new T(); // fixed, was T.new()
}
}
public class ChildClass : ParentClass<ChildClass> {
public ChildClass() { }
}
Otherwise go for the ReflectionCode by Ravadre.
I'm using the following pattern.
Pros:
This pattern secure the type-safety of cloning in private and public sides of classes.
The output class will be always correct.
You never forgot override the "clone" method. The "MyDerivedClass" never returns another class than the "MyDerivedClass".
Cons:
For one class, you need create one interface and two classes (prototype and final)
Sample:
// Common interface for cloneable classes.
public interface IPrototype : ICloneable {
new IPrototype Clone();
}
// Generic interface for cloneable classes.
// The 'TFinal' is finaly class (type) which should be cloned.
public interface IPrototype<TFinal> where TFinal : IPrototype<TFinal> {
new TFinal Clone();
}
// Base class for cloneable classes.
// The 'TFinal' is finaly class (type) which should be cloned.
public abstract class PrototypeBase<TFinal> : IPrototype<TFinal> where TFinal : PrototypeBase<TFinal> {
public TFinal Clone() {
TFinal ret = this.CreateCloneInstance();
if ( null == ret ) {
throw new InvalidOperationException( "Clone instance was not created." );
}
this.FillCloneInstance( ret );
return ret;
}
// If overriden, creates new cloned instance
protected abstract TFinal CreateCloneInstance();
// If overriden, fill clone instance with correct values.
protected abstract void FillCloneInstance( TFinal clone );
IPrototype IPrototype.Clone() { return this.Clone(); }
object ICloneable.Clone() { return this.Clone(); }
}
// Common interface for standalone class.
public interface IMyStandaloneClass : IPrototype<IMyStandaloneClass> {
string SomeText{get;set;}
string SomeNumber{get;set;}
}
// The prototype class contains all functionality exception the clone instance creation.
public abstract class MyStandaloneClassPrototype<TFinal> : PrototypeBase<TFinal>, IMyStandaloneClass where TFinal : MyStandaloneClassPrototype<TFinal> {
public string SomeText {get; set;}
public int SomeNumber {get; set}
protected override FillCloneInstance( TFinal clone ) {
// Now fill clone with values
clone.SomeText = this.SomeText;
clone.SomeNumber = this.SomeNumber;
}
}
// The sealed clas contains only functionality for clone instance creation.
public sealed class MyStandaloneClass : MyStandaloneClassPrototype<MyStandaloneClass> {
protected override MyStandaloneClass CreateCloneInstance() {
return new MyStandaloneClass();
}
}
public interface IMyExtendedStandaloneClass : IMyStandaloneClass, IPrototype<IMyExtendedStandaloneClass> {
DateTime SomeTime {get; set;}
}
// The extended prototype of MyStandaloneClassPrototype<TFinal>.
public abstract class MyExtendedStandaloneClassPrototype<TFinal> : MyStandaloneClassPrototype<TFinal> where TFinal : MyExtendedStandaloneClassPrototype<TFinal> {
public DateTime SomeTime {get; set;}
protected override FillCloneInstance( TFinal clone ) {
// at first, fill the base class members
base.FillCloneInstance( clone );
// Now fill clone with values
clone.SomeTime = this.SomeTime;
}
}
public sealed class MyExtendedStandaloneClass : MyExtendedStandaloneClassPrototype<TFinal> {
protected override MyExtendedStandaloneClass CreateCloneInstance() {
return new MyExtendedStandaloneClass
}
}