QUESTION IS CLARIFIED
new thread : subclass properties accessed in generic method with superclass input
I have a base class A
subClasses B, C, and D inherit from A.
Each subClass has 3 subClasses a, b, and c.
a, b, and c have a list of unique properties.
However, now I want to build a generic function to access those properties, so how would I do this without switching on Type?
Clarification : I do not want a : B to have abstract C methods/properties
Example:
public void Method(A a){
if(a.isSubClassOf(B))
{Console.WriteLine(a.BaProperty);}
if(a.isSubClassOf(C))
{Console.WriteLine(a.CbProperty);}
if(a.isSubClassOf(D))
{Console.WriteLine(a.DcProperty);}
}
You can't define a member in derived class and access it via the reference to base class without casting to derived class:
class A {}
class B
{
public int i;
}
A a = new B();
a.i = 0; // error
((B)a).i = 0; // OK
Either declare virtual property in any of base types in your hierarchy, or use casting to the concrete derived type. Of course, in the second case your method doesn't make any sense.
Typically, you would use a virtual or abstract method defined in A and overridden in the subclasses.
public abstract class A
{
protected abstract PropertyType PropertyValue {get;}
public void Method()
{
Console.WriteLine(PropertyValue);
}
}
public class B : A
{
protected override PropertyType Property { get { return PropertyType.B; } }
}
// etc...
An elegant solution is to override ToString
public abstract class A { }
public class B : A {
public int b { get; set; }
public override string ToString()
{
return b.ToString();
}
}
// Do the same with C and D ....
A[] array = new A[] { new B(), new C(), new D() };
foreach (A a in array) {
Console.WriteLine(a);
}
Note that Console.WriteLine does not need to know about a special method or property in A. It also works for types not deriving from A.
It depends greatly in what you really want to achieve. In some cases what Steve Czetty suggests is the best option.
In others you could just keep all the properties different and have a virtual method in the base class that returns for example in this case a "string" that you can then write in the console or anything you wish.
Edit: You could override ToString as Olivier suggested. But only if you feel what yo are going to retun is the "String representation of the object".
public abstract class A
{
public string PropertyA { get; set; }
public virtual string GetString() //
{
return PropertyA;
}
}
public class B:A
{
public string PropertyB { get; set; }
public override string GetString()
{
return PropertyB;
}
}
public class C:A
{
public string PropertyC { get; set; }
public override string GetString()
{
return string.Format("{0} - {1}", base.GetString(), PropertyC) // for example if you wanted to do something more complex
}
}
Now if what you need can not be solved like this, you could cast as Dennis Suggested.
There is another posibility: you could use the visitor pattern. Here you can find several ways to implement it.
Just so you have an idea you would wind up having a class similar to this: (it will depend on what you really want to achieve)
You have to implement some other basic things (interface and some methods), but from a Reference to the base class you will be able to call the corresponding "Visit" method easily. There is a lot of detail in the link i added.
class ClassicVisitor : IAVisitor
{
public string SuperComplexStringResult { get;set; }
public void Visit(B b) { SuperComplexStringResult = String.Format("Super Complex Stuff + {0}", b.PropertyB); }
public void Visit(C c) { SuperComplexStringResult = String.Format("Super Complex Stuff + {0}", c.PropertyC); }
}
Related
My base class has a method to serialize itself that I want derived classes to use.
public abstract class Base
{
public int Property1 { get; set; }
public virtual string Serialize()
{
...
return System.Text.Json.JsonSerializer.Serialize(this, jsonSerializerOptions);
}
}
The problem is that "this" in the base classes refers to the base class. When calling Serialize() from derived classes, only the properties of the base class are serialized. What can I use instead of "this" to pass to the Json serializer so that it will refer to the instance of the derived class.
Derived class may look like this:
public class Derived : Base
{
public int Property2 { get; set; }
}
I then call the Serialize() method like this:
Derived derived = new Derived();
string json = derived.Serialize();
Only Property1 is serialized.
The reason of it serialize Property1 only is you didn't override the virtual method in the derived class, So it works only for property1.
Sample:
public abstract class Base
{
public int Property1 { get; set; } = 20;
public virtual void Display()
{
MessageBox.Show(Property1.ToString());
}
}
public class Derived : Base
{
public int Property2 { get; set; } = 9;
public override void Display() //without this you can't achieve what you want
{
base.Display();
MessageBox.Show(Property2.ToString());
}
}
public class Test
{
public void ShowResult()
{
Derived derived = new Derived();
derived.Display();
}
}
Test test = new Test();
{
test.ShowResult();
}
OUTPUT
Two Messageboxes
First displays: 20
Second displays: 9
If I didn't override the virtual method in the derived class the OUTPUT would be:
One Messageboxe ONLY
Displays: 20
From Documentation
When a virtual method is invoked, the run-time type of the object is
checked for an overriding member. The overriding member in the most
derived class is called, which might be the original member, if no
derived class has overridden the member.
we can't change 'this' behavior, but you can try below solution, its work like what you need
class Program
{
static void Main(string[] args)
{
Derived d = new Derived();
Console.WriteLine(d.Serialize());
Console.ReadLine();
}
}
public abstract class Base
{
public int Property1 { get; set; }
}
public class Derived : Base
{
public int Property2 { get; set; }
}
public static class Extensions
{
public static string Serialize(this Base obj)
{
return System.Text.Json.JsonSerializer.Serialize((object)obj);
}
}
The overload method you are using is Serialize< BaseClass >(this, options). This when called from the base class always pass the BaseType as T.
Fortunately, JsonSerializer provides another overload which you can use from baseclass and achieve the desired behavior without overriding in derived class. For this, You should be using Serialize(this,this.GetType(),options). this.GetType() wil always returns the instance type even when call is done from a base class.
With the abstract following class:
public abstract class A
{
public static string MyMethod()
{
return "a";
}
}
Why can't I built this derived abstract class:
public class B<T> where T : A
{
public void AnotherMethod()
{
var S1 = base.MyMethod(); // not allowed
var S2 = T.MyMethod(); // not allowed
}
}
I don't understand why since MyMethod will be available in type T.
There are two misconceptions in your question that collectively prevent both your attempts from working.
First your B class is not in any way derived from the A class, you have only said that it takes a generic parameter that must inherit from A.
Second as the user #recursive pointed out, static methods do not participate in inheritance so MyMethod would only ever be available as A.MyMethod()
You can make at least your first attempt work if you remove the static modifier and make B inherit from A instead of using generics.
// Removed the static modifier
public abstract class A
{
public string MyMethod()
{
return "a";
}
}
// Made B inherit directly from A
public class B : A
{
public void AnotherMethod()
{
var S1 = base.MyMethod(); //base technically isn't required
}
}
Aside from the fact that A.MyMethod is static, which clearly will not work since anything static does not take part in inheritance, even if you made it not static it still will not work. For example, this will not work either:
public abstract class A {
public string MyMethod() {
return "a";
}
}
public class B<T> where T : A {
public void AnotherMethod() {
var S1 = base.MyMethod(); // Line 1
var S2 = T.MyMethod(); // Line 2
}
}
Why?
You are saying where T : A which means that type T has to be a derived type from A. Your class B<T is not a derived type of A so Line 1 will not work.
But why is Line 2 not working?
T is a type and if T is inheriting A, then objects of type T will be able to do that. If you changed it like this, then it will work:
public abstract class A {
public string MyMethod() {
return "a";
}
}
public class B<T> where T : A {
public void AnotherMethod(T t) {
t.MyMethod();
}
}
public class C : A {
}
public class BClosed : B<C> {
public void Foo(C c) {
c.MyMethod();
this.AnotherMethod(c);
}
}
In the above code, C derives A which was your restriction. Then BClosed closes the generic type saying T is C so now you can call MyMethod of A and AnotherMethod of your generic.
Also, when you have a generic class you should use the generic type otherwise I do not see the use. So this is useless since it has no generic code:
public class B<T> where T : A {
public void AnotherMethod() {
}
}
I have a Function in C# and it have to return the type of the Class. Also in subclasses which extends the class.
Like:
public class A
{
public typeof(this) Method()
{
//Code
}
}
public class B : A {
public override typeof(this) Method() {
//Code
}
}
So the Method in class A should have the return type A. And the Method in class B should have the return tpye B.
Is there a way to do it?
No, this isn't possible. What you're asking for is called a covariant return type, but C# doesn't support this. The closest you can get is either this:
public class A
{
public virtual A Method()
{
//Code returning an A
}
}
public class B : A
{
public override A Method()
{
//Code returning a B
}
}
Which is legal because every B is also an A, or you can use generics instead of inheritance:
public class Foo<T>
{
public virtual T Method()
{
//Code
}
}
And then you can have Foo<A> and Foo<B> -- however, Foo cannot depend on any specifics of T. You can combine this with inheritance, which will sort of achieve what you want:
public class A : Foo<A>
{
// And now A has a Method that returns A
}
public class B : Foo<B>
{
// And now B has a Method that returns B
}
But the problem with this approach is that you will have a hard time actually implementing Method in a meaningful way, because in Foo you cannot use anything specific to the type. To make this explicit, you could make Method abstract:
public abstract class Foo<T>
{
public abstract T Method();
}
public class A : Foo<A>
{
public override A Method()
{
// Code
}
}
public class B : Foo<B>
{
public override B Method()
{
// Code
}
}
I'm having a hard time imagining a scenario where you can actually make use of this, but at least it meets the requirements.
Last but not least, you are not required to use inheritance -- does B really need to derive from A or could you inherit from some common base that does not use Method?
Depending on what your method is trying to do, it might be possible to achieve what you want by using extension methods.
public class A { }
public class B : A { }
public static class AExtension {
public static T Method<T>(this T target) where T: A {
// do your thing here.
return target; // or, return a new instance of type T.
}
}
You can then call Method() and let C# infer the generic argument:
var a = new A();
a = a.Method(); // C# will infer T as A.
var b = new B();
b = b.Method(); // C# will infer T as B.
The downside to this approach is, of course, that you cannot access non-public members of your classes in Method(), unless you use reflection.
There is a way to do this, actually.
class A {
public A Method () { ... return this; }
}
class B : A {
new public B Method () => (B)base.Method();
// or { base.Method(); return this; }
}
Make sure you only use this if you know that the base returns this.
I've been searching for a bit and found similar things but nothing that quite answers my question. Here it is- I have two classes. A, B. I want class C to have all the properites of those two classes. This is in the Object Layer, c#.net.
Class A:
public class A
{
public string property1 { get; set; }
}
public class B
{
public string anotherproperty { get; set; }
}
public interface IB
{
B b { get; set; }
}
public class C : A, IB
{
//nothing here cause hopefully it inherits everything
}
I have no idea if my implementation is even close. I do get error message of "C does not implement interface member IB"
Anyone know how to do this?
I have two classes. A, B. I want class C to have all the properites of those two classes.
...then you will have to manually add either A's or B's properties to C. C# does not support multiple inheritance, sorry.
However, in most cases multiple inheritance is not needed. A common alternative is to use composition instead of inheritance: For example, you could have your class C provide references to instances of A and B:
public class C
{
private A a = new A();
private B b = new B();
public A A { get { return a; } }
public B B { get { return b; } }
}
This would allow you to access all properties via myC.A.property1 and myC.B.anotherproperty.
If you really need to combine implementations from both A and B in C, you might need to have a look at Mixin libraries for C#.
You can do something like this:
public class ClassA
{
public string AProp { get { return "AProp";} }
}
public class ClassB : ClassA
{
public string BProp { get { return "BProp"; } }
}
public class ClassC : ClassB
{
}
And then:
ClassC c = new ClassC();
Console.WriteLine(c.AProp);
Console.WriteLine(c.BProp);
Prints:
AProp
BProp
You can't override anything but you can access the inherited properties.
I have case where am given a collection of objects that all derive from the same base class. If I iterate over the collection and check each item's type, I can see that the object is of a derived type and then handle it accordingly. What I would like to know is if there is an easier way of performing the check for the derived type besides what I am already doing. Code repetition typically isn't required, so my current methodology seems a bit off to me.
class A {}
class B : A {}
class C : A {}
class D : C {}
class Foo
{
public List<A> Collection { get; set; }
}
class Bar
{
void Iterate()
{
Foo f = new Foo();
foreach(A item in f.Collection)
{
DoSomething(a);
}
}
void DoSomething(A a)
{
...
B b = a as B;
if(b != null)
{
DoSomething(b);
return;
}
C c = a as C;
if(c != null)
{
DoSomething(c);
return;
}
D d = a as D;
if(d != null)
{
DoSomething(d);
return;
}
};
void DoSomething(B a){};
void DoSomething(C a){};
void DoSomething(D a){};
}
I am working with a web service where every web service must have the same result type.
class WebServiceResult
{
public bool Success { get; set; }
public List<Message> Messages { get; set; }
}
class Message
{
public MessageType Severity { get; set; } // Info, Warning, Error
public string Value { get; set; } //
}
class InvalidAuthorization: Message
{
// Severity = MessageType.Error
// Value = "Incorrect username." or "Incorrect password", etc.
}
class InvalidParameter: Message
{
// ...
}
class ParameterRequired: InvalidParameter
{
// Severity = MessageType.Error
// Value = "Parameter required.", etc.
public string ParameterName { get; set; } //
}
class CreatePerson: Message
{
// Severity = MessageType.Info
// Value = null
public int PersonIdentifier { get; set; } // The id of the newly created person
}
The goal is that we can return as many different types of messages back to the client as we want. Instead of getting a single message per web service call, the callee can know about all of their mistakes/successes in a single trip and to eliminate string parsing specific information from the message.
I originally though about using generics, but since the web service could have varying message types, the collection was broadened to use the base message class.
It may be possible to move DoSomething to A and have each subclass provide their own implementation:
public abstract class A
{
abstract void DoSomething();
}
void Iterate()
{
Foo f = new Foo();
foreach(A item in f.Collection)
{
item.DoSomething();
}
}
An idea would be to use a generic constraint on your base class or an interface.
public class MyClass<T> where T : BaseClass, IInterface
{
public void executeCode<T>(T param) {};
}
So MyClass<T> takes only a certain type, executeCode will have an idea what methods are exposed and what operations can be performed on the data of the object passed.
This avoids the need to cast because you are specifying a contract that must be followed.
typeof(ParentClass).IsAssignableFrom(typeof(ChildClass));
Return true is the cast is possible.
Also possible this way:
typeof(ParentClass).IsAssignableFrom(myObject.GetType());
But in your example, you actually call a methods for each object type. So you would need the cast anyway, unless you don't mind refactoring to not have a collection of overload.
Something like this if you want to keep the overload:
foreach(A item in f.Collection)
{
Type itemType = item.GetType();
if (typeof(B).IsAssignableFrom(itemType)
DoSomethingB(item);
else if (typeof(C).IsAssignableFrom(itemType)
DoSomethingC(item);
//...
}
EDIT: I like more Lee's answer. Adding virtual/override function to the class type would be a better design and way easier to handle, unless the DoSomething really has nothing to do being in the classes.
Lee is right. Just let the item decide, what to do. It knows it's type best and therefore knows what to do. You might even give some standard implementation, if it is the same as in A, by not making it abstract, but virtual. Be aware though, that the compiler wont ask for an implementation then.
public class A
{
public virtual DoSomething(){"What A needs doning!"}
}
public class B : A
{
public override DoSomething() {"What B needs doing!"}
}
Another way would be the use of Interfaces.
public interface IAinterface
{
void DoSomething();
}
public class A : IAinterface
{
void DoSomething(){...}
}
public class B : IAinterface
{
void DoSomething(){...}
}
This would be more like Lees suggestion, although interfaces and abstract base classes work a bit different in the background.
I usually prefer the upper one, because I usually tend to give the base class some standard behavior and only implement derived classes, when there is something different.