Explanation:
I have an abstract class like so:
public abstract class Serializer<T> where T : new()
{
T obj { get; set; }
public string ToXML()
{
// return string XML
}
}
And another class that inherits this abstract class:
public class Account : Serializer<Account>
{
// Code
// I don't want to have to implement the methods of
// the inherited class/interface.
}
I want to access it like such:
Account account = new Account();
Console.WriteLine(account.ToXML());
Question:
Can I do this and pass the account to the property obj so the ToXML can perform its task of converting the object to a string?
Serializer s = new Serializer();
s.ToXML(account);
I'd prefer to have each object inherit the Serialize class and all its methods, and just be able to know that without editing anything but adding the inheritance of the class that I can now access these methods.
On another note, I feel like inheriting a class violates the is-a and can-do principles between choosing an interface or a class, but I don't want to override all the methods, when I already have the code written to do it generically in a class (i.e., I don't want to implement the interface). Is there a way to inherit the methods of an interface like a class (no implementing/overriding).
Try to return this:
T obj { get { return (T)this; } }
But, this means that the child class has to provide itself as a type parameter, it's the curiously recurring "template" pattern... To be sure though, you don't necessarily need to know the type of the object at compile time to serialize it to XML (if you use the usual serializers), so accessing this within the serializer method would be OK, without the need for that type parameter and that property.
I'd personally prefer a more hands off approach to an abstract base class (using the XmlSerializer):
public interface MXmlSerializable { }
public static class XmlSerializable {
public static string ToXml(this MXmlSerializable self) {
if (self == null) throw new ArgumentNullException();
var serializer = new XmlSerializer(self.GetType());
using (var writer = new StringWriter()) {
serializer.Serialize(writer, self);
return writer.GetStringBuilder().ToString();
}
}
}
M stands for mixin. It's effectively a marker interface with an extension method. Use it like this:
public class Account : MXmlSerializable {
...
}
...
Account account = new Account();
...
string accountXml = account.ToXml();
Your construct hardly makes sense. There's no clear point for the Serializer<T> instance to point to itself. You can easily use this and cast it to T. Also, unless your ToXML method implements some really generic XML serialization algorithm (like processing the current instance via reflection), you should make it virtual and place the specific implementations in Serializer<T>'s ancestors.
Also, I would also object your approach to inheritance. If your Account class is in fact a single purpose account serializer, then name it so (AccountSerializer). If not, and Account represents an actual account, then yes, from an independent reader's point of view you are mixing two primary concepts: a business object (Account) and some technical mechanism (Serializer<T>).
If you have a general-purpose serialization algorith, why don't you just have a separate, non-abstract Serializer<T> class, accepting T instances in ToXML()? You will end up with better separation of concerns.
Is there a way to inherit the methods of an interface like a class (no implementing/overriding).
No. Interfaces are interfaces, not classes than embed particular code.
What about just doing it like this;
public string ToXML()
{
convert `this` to xml directly
// return string XML
}
Why do you need the property to return a reference to the class itself.
With the above structure you can do the following, without even needing the T property
Account account = new Account();
Console.WriteLine(account.ToXML());
If your code in the Abstract class will not change just to serialize the object, this approach doesn't make sense, Serialization you do not need to know the object type (Especially if your using xml which means building a easy to access string).
If you want the Serialization only available to certain objects make an interface i.e
public interface ISerialize
{
}
public class Account : ISerialize
{
}
and then create an Extension method
public static class ExtenstionMethods
{
public static string ToXml(this ISerialize obj)
{
// code to build xml string
}
}
This way you can do what you want to do because Account is of the Interface and the ExtensionMethods will only work on that Interface, thus you only need the code in the ExtensionMethods class and then include the namespace wherever you want to use the "ToXml()" etc
Account account = new Account();
Console.WriteLine(account.ToXML());
Related
Pretty straightforward question. I want to allow only DTO models in inputs (class & record types).
If I leave the class constraint only, I'm still able to put string in there. I want to not allow the primitive types.
If I put class, new(), it doesn't allow string just as expected, but I'm not allowed to use positional records either which is a problem.
public class Asd
{
public string Name { get; set; }
}
public record Asd2(string Name);
public Task DoSomethingAsync<TInput>(TInput data) where TInput : class
{
var message = JsonSerializer.Serialize(data); // if TInput is a string, it results into faulty \u0022 codes
}
Edit: The actual issue is that I have JsonSerializer.Serialize(data) inside that method and if a string is passed accidentally, it will result in something like:
"{\u0022Name\u0022:\u0022Test\u0022}"
You need to have some kind of commonality for the restriction.
This needs to be a common base class or interface.
As you want to use Records as well, then this must be an interface. But you can just define a simple, empty one if you want just for this purpose.
So you define a simple empty interface (better is if you actually have some common functions/properties).
public interface MyInterface
{
}
So then you code looks like this
public Task DoSomethingAsync<TInput>(TInput data) where TInput : MyInterface
{
}
And all your classes and records inherit from it like this.
public record AsdRecord: MyInterface
{
//details here
}
public class AsdClass: MyInterface
{
//details here
}
If your list of allowed types can't be formulated with a type constraint, consider creating a list of allowed types (either hardcoded in code or with reflection at runtime e.g. on the namespace) and test against that list at runtime right at the beginning of the method (like you also test incoming parameters). Maybe something like this
private static readonly HashSet<Type> AllowedTypes = new HashSet<Type>
{
typeof(MyTypeA),
typeof(MyTypeB),
};
public Task DoSomethingAsync<TInput>(TInput data)
{
if(!AllowedTypes.Contains(typeof(TInput)))
throw new ArgumentException($"The type {typeof(TInput).Name} can' t be used here.");
// ...
}
While this doesn't help you at compile time, at least it helps you at runtime.
I have a factory object ChallengeManager to generate instances of a Challenge object for a game I'm building. There are many challenges. The constructors for each Challenge class derivation are different, however there is a common interface among them, defined in the base class.
When I call manager.CreateChallenge(), it returns an instance of Challenge, which is one of the derived types.
Ideally, I would like to keep the code for the object construction inside the derived class itself, so all the code related to that object is co-located. Example:
class Challenge {}
class ChallengeA : Challenge {
public static Challenge MakeChallenge() {
return new ChallengeA();
}
}
class ChallengeB : Challenge {
public static Challenge MakeChallenge() {
return new ChallengeB();
}
}
Now, my ChallengeManager.CreateChallenge() call only needs to decide the class to call MakeChallenge() on. The implementation of the construction is contained by the class itself.
Using this paradigm, every derived class must define a static MakeChallenge() method. However, since the method is a static one, I am not able to make use of an Interface here, requiring it.
It's not a big deal, since I can easily remember to add the correct method signature to each derived class. However, I am wondering if there is a more elegant design I should consider.
I really like the pattern you are describing and use it often. The way I like to do it is:
abstract class Challenge
{
private Challenge() {}
private class ChallengeA : Challenge
{
public ChallengeA() { ... }
}
private class ChallengeB : Challenge
{
public ChallengeB() { ... }
}
public static Challenge MakeA()
{
return new ChallengeA();
}
public static Challenge MakeB()
{
return new ChallengeB();
}
}
This pattern has many nice properties. No one can make a new Challenge because it is abstract. No one can make a derived class because Challenge's default ctor is private. No one can get at ChallengeA or ChallengeB because they are private. You define the interface to Challenge and that is the only interface that the client needs to understand.
When the client wants an A, they ask Challenge for one, and they get it. They don't need to worry about the fact that behind the scenes, A is implemented by ChallengeA. They just get a Challenge that they can use.
You're "decentralizing" the factory, such that each subclass is responsible for creating itself.
More commonly you would have a central factory that would know about the possible subtypes and how to construct them (often enough, simply by creating a new instance and returning that instance typed as a common interface or common base class). That approach avoids the issue you currently have. I also see no benefit to your current approach. You are currently gaining no encapsulation or code reuse over the more typical implementation of a factory.
For additional reference, have a look at
http://www.oodesign.com/factory-pattern.html
Not necessarily the answer you are looking for but...
You can use following implementation, if you can move away from static method per class.
using System;
public class Test
{
public static void Main()
{
var c1 = ChallengeManager.CreateChallenge();
var c2 = ChallengeManager.CreateChallenge();
//var c = ChallengeManager.CreateChallenge<Challenage>(); // This statement won't compile
}
}
public class ChallengeManager
{
public static Challenage CreateChallenge()
{
// identify which challenge to instantiate. e.g. Challenage1
var c = CreateChallenge<Challenage1>();
return c;
}
private static Challenage CreateChallenge<T>() where T: Challenage, new()
{
return new T();
}
}
public abstract class Challenage{}
public class Challenage1: Challenage{}
public class Challenage2: Challenage{}
I'm reposting a question I've just asked, but want to re-ask this question in a more concise way as I think I was causing some confusion.
I have a base class: RoomObject.
I have two subclasses: Bed and Table, which inherit from RoomObject.
I have a variable currentObject, which is of type RoomObject, but will actually hold either an instance of Bed or Table (RoomObject is never instantiated itself).
How can I clone my currentObject, without knowing its full type?
i.e. if currentObject is a Bed, I want to clone the Bed using
currentObject = new Bed(currentObject);
and if currentObject is a Table, I want to use
currentObject = new Table(currentObject);
I could use reflection, by calling Activator.CreateInstance(currentObject.GetType()), and then copy across any attributes I need, but this seems messy.
You should use the pattern known as the virtual constructor, or a cloning method.
Add a virtual method to RoomObject that returns a copy of the current object:
abstract RoomObject Clone();
Now implement this method in Bed to return new Bed(...), and in the Table to return new Table(...). Pass whatever parameters necessary to the constructors of Bed and Table to copy what's in the current object.
.NET has an interface ICloneable that is commonly used to implement this pattern. A small disadvantage of that approach is that Clone must return object, not RoomObject, so if you need RoomObject, you'd need to cast it.
This is one of the best things about reflection: The ability to create an object without your client code knowing what type it is. Sometimes it can get messy, or even slow down the code at times, but--if used correctly--will make your code a lot more manageable.
For example, take a look at the Factory Pattern, and how one can implement it with Reflection and here as well
I think one solution would be implement ICloneable interface for all your objects. Here's some sample code:
class RoomObject : ICloneable
{
public abstract object Clone();
}
class Bed : ICloneable
{
public override object Clone()
{
return new Bed();
}
}
class Table : ICloneable
{
public override object Clone()
{
return new Table();
}
}
class Program
{
public static void Main(String[] args)
{
RoomObject ro = /* from some other places*/
RoomObject newOne = ro.Clone() as RoomObject; /* here's what you what */
}
}
Instead of that, implement the ICloneable interface that's out-of-the-box on .NET Framework as others said in their answers.
Since ICloneable.Clone() method returns object, what about a custom ICloneable<T> that also implements ICloneable?
public interface ICloneable<T> : ICloneable
where T : class
{
T TypedClone();
}
public class MyCloneableObject : ICloneable<MyCloneableObject>
{
public string Some { get; set; }
public object Clone()
{
MyCloneableObject clone = new MyCloneableObject { Some = this.Some };
}
public MyCloneableObject TypedClone()
{
return (MyCloneableObject)Clone();
}
}
Later, in your code...
MyCloneableObject some = new MyCloneableObject();
if(some is ICloneable<MyCloneableObject>)
{
MyCloneableObject myClone = some.TypedClone();
// .. or the standard `Clone()`:
myClone = (MyCloneableObject)some.Clone();
}
Implementing both built-in and custom interface is a good idea, as your cloneable will operate with other libraries that may accept ICloneable implementations.
Finally, rather than using reflection, this case should be solved in design-time. I would argue that doing with reflection should be done if you can't modify the library containing the ICloneable wannabe.
I need to define a static property or method in certain classes of my bussiness logic, to explicity determine which classes are cacheables in Session or Cache of ASP.NET service. I'm thinking, static property or method in the interface would be perfect, but C# 4.0 doesn't support this.
All a need is be able to evaluate in a generic manager which classes are cacheables and, if they are, at what level: session (user) or cache (application).
Now I'm trying with a empty interface with T parameter to evaluate, but, maybe exists a better approach?? Thanks.
public interface ICacheable<T>
{
}
public class Country : ICacheable<CacheApplication>
{
}
public class Department : ICacheable<CacheUser>
{
}
public class Gestor<T>
{
// ...
if (typeof(T) is ICacheable<CacheApplication>)
{
}
// ...
}
How about using a custom attribute? Your classes then would look something like this:
[Cacheable(Level = CacheLevels.Application)]
public class Country { }
[Cacheable(Level = CacheLevels.User)]
public class Department { }
You can read here on how to create your own custom attribute and then access its value by using reflection.
You cant define static interfaces, for one thing, you cant make instances of static classes so you cant substitute them for others with the same base class.
You might be better off having a singleton instance of one class and using interfaces as normal. You could enforce one and one-only instance through a factory pattern too.
I recently ran into a problem where it seems I need a 'static abstract' method. I know why it is impossible, but how can I work around this limitation?
For example I have an abstract class which has a description string. Since this string is common for all instances, it is marked as static, but I want to require that all classes derived from this class provide their own Description property so I marked it as abstract:
abstract class AbstractBase
{
...
public static abstract string Description{get;}
...
}
It won't compile of course. I thought of using interfaces but interfaces may not contain static method signatures.
Should I make it simply non-static, and always get an instance to get that class specific information?
Any ideas?
You can't.
The place to do this is with Attributes.
Eg
[Name("FooClass")]
class Foo
{
}
If you don't mind deferring to implementations to sensibly implement the Description property, you can simply do
public abstract string ClassDescription {get; }
// ClassDescription is more intention-revealing than Description
And implementing classes would do something like this:
static string classDescription="My Description for this class";
override string ClassDescription { get { return classDescription; } }
Then, your classes are required to follow the contract of having a description, but you leave it to them to do it sensibly. There's no way of specifying an implementation in an object-oriented fashion (except through cruel, fragile hacks).
However, in my mind this Description is class metadata, so I would prefer to use the attribute mechanism as others have described. If you are particularly worried about multiple uses of reflection, create an object which reflects over the attribute that you're concerned with, and store a dictionary between the Type and the Description. That will minimize the reflection (other than run time type inspection, which isn't all that bad). The dictionary can be stored as a member of whatever class that typically needs this information, or, if clients across the domain require it, via a singleton or context object.
If it is static, there is only one instance of the variable, I don't see how inheritance would make sense if we could do what you want to accomplish with static vars in derived classes. Personally I think you are going to far to try to avoid a instance var.
Why not just the classic way?
abstract class AbstractBase
{
protected string _Description = "I am boring abstract default value";
}
class Foo : AbstractBase {
public Foo() {
_Description = "I am foo!";
}
}
Combining static and abstract is somewhat meaningless, yes. The idea behind static is one need not present an instance of the class in order to use the member in question; however with abstract, one expects an instance to be of a derived class that provides a concrete implementation.
I can see why you'd want this sort of combination, but the fact is the only effect would be to deny the implementation use of 'this' or any non-static members. That is, the parent class would dictate a restriction in the implementation of the derived class, even though there's no underlying difference between calling an abstract or 'static abstract' member (as both would need a concrete instance to figure out what implementation to use)
A possible workaround is to define a Singleton of your derived class in your base class with the help of Generics.
import System;
public abstract class AbstractBase<T>
where T : AbstractBase<T>, new()
{
private static T _instance = new T();
public abstract string Description { get; }
public static string GetDescription()
{
return _instance.Description;
}
}
public class DerivedClass : AbstractBase<DerivedClass>
{
public override string Description => "This is the derived Class";
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine(DerivedClass.GetDescription());
Console.ReadKey();
}
}
The trick is to tell your AbstractBase<T> some details about how DerivedClass is implemented:
It is newable with where T: new() so it can create a Singleton instance
It derives from itself with where T : AbstractBase<T> so it knows that there will be a implementation of Description
This way _instance contains the Description field which can be called in the static Method GetDescription().
This forces you to overwrite Descriptionin your DerivedClass and allows you to call its value with DerivedClass.GetDescription()
It's not static if it has to be called on an instance.
If you're not calling it on an instance, then there's no polymorphism at play (i.e. ChildA.Description is completely unrelated to ChildB.Description as far as the language is concerned).
You can...
In the abstract class...
protected abstract InWindow WindowInstance { get; set; }
In the derived class...
private static InWindow _instance;
protected override InWindow WindowInstance
{
get => _instance;
set => _instance = value;
}
You could make the "abstract" base method throw an Exception, so then a developer is "warned" if he tries to invoke this method on a child class without overriding.
The downside is that one might extend the class and not use this method. Then refer to other answers provided.