Im not sure if it is possible. I am running into a unique issue dealing with a clients api.
I am needing to extend a class and add a bool property that does not exist in the base class.
below is an example of what I am trying to accomplish.
public class baseClass
{
//.. No Editable Access
}
public class Extended
{
public bool flaggedAsDeleted(this baseClass bc)
{
//Idealy was looking for get; set; but I know that don't work
return true;// Need to know if possible to set property on baseClass or Alternative
}
public void flagAsDeleted(this baseClass bc)
{
flaggedAsDeleted = true;
}
}
public class program
{
public void doit()
{
baseClass bc = new baseClass();
bc.flagAsDeleted();
}
}
If you're trying to actually extend a class, you do it like this:
public class BaseClass
{
//.. No Editable Access
}
public class Extended : BaseClass
{
public bool FlaggedAsDeleted { get; set; }
}
If you're trying to add data to an existing class, you have two options:
Inheritance - as seen above.
Encapsulation - create a new object that holds an instance of the type you're adding to.
C# provides a feature called Extension Methods, which allows you to seemingly add methods to existing classes. However, these are really just syntactic sugar, as you're still constrained to the class's public API.
public class BaseClass
{
public int Value { get; set; }
}
public static class ExtensionMethods
{
public static void Increment(this BaseClass b)
{
b.Value += 1;
}
}
Extension methods do not allow you to add data to an existing class though.
This is not unique. This is a common problem solved using a Design Pattern called decorator.
Related
I have an interface such as this one:
public interface ITestInterface
{
int a { get; set; }
void DoSomething();
}
Some of my classes are deriving from this interface:
public class OneClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine(this.a.ToString());
}
}
public class AnotherClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine((this.a * 2).ToString());
}
}
Since I now need a (large) common method on all classes derived from my interface, I was trying to provide an additional base class for that:
public class MyBaseClass
{
public void LargeCommonMethod()
{
Console.WriteLine((this.a * 3).ToString()); // no 'a' on base class
}
}
This clearly doesn't work because the base class would also need to implement my interface in order to know about that a field.
I am now asking myself what the best approach would be here:
make MyBaseClass inherit from ITestInterface?
set LargeCommonMethod() to protected and provide all internal data it uses via arguments? (There's actually a lot of these..)
skip the interface all along and replace it with an abstract base class?
...?
C# 8 provides a feature precisely for this scenario.
Your classes all implement an interface
You want to add a method to the interface
You don't want a breaking change to all of the existing classes. If you add a method to the interface all of the classes will break unless you find some way to add the method to all of them. (That includes modifying them all to inherit from a new base class.)
That feature is default interface methods.
You can add your method and a default implementation to the interface:
public interface ITestInterface
{
int a { get; set; }
void DoSomething();
void LargeCommonMethod()
{
Console.WriteLine((this.a * 3).ToString());
}
}
Your existing classes that implement the interface will not break. When cast as the interface, you'll be able to call the method which is defined in the interface. You can still modify any class to provide its own implementation, overriding the interface's default implementation.
For the method to be available the object must be cast as the interface - ITestInterface.
A lot of developers - including myself - found this to be an odd feature. But this is the scenario it's for.
Some documentation
The most common scenario is to safely add members to an interface already released and used by innumerable clients.
If you require a base implementation for a method then an interface is clearly not the way to go.
I would choose an abstract class instead and get rid of the interface. There is no need to complicate the design basically.
The Adapter pattern could fit your Use case, when you want to keep the ITestInterface consistent:
public interface ITestInterface
{
int a { get; set; }
void DoSomething();
}
public class TestInterfaceAdapter : ITestInterface
{
private readonly ITestInterface _testInterface;
public int a {
get => _testInterface.a;
set => _testInterface.a = value;
}
public TestInterfaceAdapter(ITestInterface testInterface)
{
_testInterface = testInterface;
}
public void DoSomething()
{
_testInterface.DoSomething();
}
public void LargeCommonMethod()
{
Console.WriteLine((this.a * 3).ToString());
}
}
public class OneClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine(this.a.ToString());
}
}
public class AnotherClass : ITestInterface
{
public int a { get; set; }
public void DoSomething()
{
Console.WriteLine((this.a * 2).ToString());
}
}
I tried to search for solutions, but my problem is I don't even know what terms to use. Generics, Delegates, LINQ, Reflection, and Abstract ideas could be part of the solution, but my "Google-fu" isn't turning up the right answer.
Question:
I have multiple classes (ClassA, ClassB, ClassC) that all have the same 2-3 properties DoThisA, DoThisB, DoThisC.
The way the code works is that I always want to do the same code to set DoThisA, DoThisB, and DoThisC when I process each of the classes.
For example, to simplify, the logic will always be:
{some computations to set string currentValueImProcessing to something}
if (xyz) [ClassA|B|C].DoThisA = currentValueImProcessing
else [ClassA|B|C].DoThisB = currentValueImProcessing
I don't want to write those same statements over and over, so how do I just send a reference to the class (A,B,C) to a method to do the logic?
If it was written correctly each of ClassA, ClassB, and ClassC would have implemented some generic class and I could use that, but I cannot. Each of the classes are independent but have the same named properties.
Any guidance on concepts/code?
Thanks!
Create an interface for your properties:
internal interface IDoThis
{
public string DoThisA { get; set; }
public string DoThisB { get; set; }
public string DoThisC { get; set; }
}
Then, make your classes implement it:
public class ClassA : IDoThis
{
public string DoThisA { get; set; }
public string DoThisB { get; set; }
public string DoThisC { get; set; }
}
public class ClassB : IDoThis
{
// Same properties
}
public class ClassC : IDoThis
{
// Same properties
}
This, way, you'll be able to create a static initializer method somewhere:
internal static class MyClassesExtensions
{
public static void InitTheStuff(this IDoThis obj)
{
// Do something here, for example:
if (String.IsNullOrEmpty(obj.DoThisA))
obj.DoThisA = "foo";
else
obj.DoThisB = obj.DoThisC;
}
}
And then you can just call this.InitTheStuff() anywhere from ClassA, ClassB and ClassC.
you can either use reflection or you can use dynamic (dynamic will use reflection for you)
dynamic obj = new ClassA();
obj.DoTHisA();
is how to do it with dynamic
I am assuming that you are talking about classes that you intend to instantiate. If DoThisA,B,C are static methods then you must use reflection
NOTE - if you can change the classes then add an interface as others have suggested, or even a common base class
The reflection one looks like this
var type = obj.GetType(); // obj is ClassX object
var method = type.GetMethod("DoTHisA");
method.Invoke(obj);
I have not checked this - so the syntax might be a bit off - but this is the basic mechanics of reflection method calling. YOu need to get fancier if there are multiple methods with the same name, if the methods takses params etc
There are at least four options open to you - maybe more.
Create an interface, which is implemented by all of your classes and that includes the common methods.
Create a base class from which all classes inherit. The common functionality can then be implemented in the base class. If the implementation differs depending on the clases, but you can define common signatures for the methods, make your base class an the common funtionality abstract. You then can implement the actual functionality in each of your classes.
Use a dynamic object as in #pm100's solution.
Use reflection to access the common functionality.
As a guidance methods 1. and 2. are to be preferred, as they allow your code to be checked on compile time. If, however, you do not have control over the classes that contain the common functionality - for example you do not have access to the source code or you are permitted to make changes to the code - you can use the other two methods.
If you'd ask me which of the two I would prefer, I guess that I would go for 3. over 4. But this is personal preference.
Prob you are talking about inheritance.
For your task you need a base abstract class with general properties:
public abstract class Base
{
public bool DoThisA { get; set; }
public bool DoThisB { get; set; }
}
and child classes:
public class A : Base { }
public class B : Base { }
public class C : Base { }
After that you can create a method which will accept object of type Base
public void Do(Base b, bool xyz, bool currentValueImProcessing)
{
if (xyz)
{
b.DoThisA = currentValueImProcessing;
}
else
{
b.DoThisB = currentValueImProcessing;
}
}
There are already many methods provided here, so just for the sake of completeness... Here's some runtime code generation:
public class ClassA
{
public string DoThisA { get; set; }
public int DoThisB { get; set; }
public bool DoThisC { get; set; }
public void Init()
{
// You can call this from anywhere, even from an unrelated class
MyClassInitializer<ClassA>.Init(this);
}
}
public static class MyClassInitializer<T>
{
// Create the getters/setters you need, and make sure they're static.
private static readonly Func<T, string> _getA = BuildGetter<string>("DoThisA");
private static readonly Action<T, string> _setA = BuildSetter<string>("DoThisA");
private static readonly Func<T, int> _getB = BuildGetter<int>("DoThisB");
private static readonly Action<T, int> _setB = BuildSetter<int>("DoThisB");
private static readonly Func<T, bool> _getC = BuildGetter<bool>("DoThisC");
private static readonly Action<T, bool> _setC = BuildSetter<bool>("DoThisC");
private static Func<T, TValue> BuildGetter<TValue>(string name)
{
var obj = Expression.Parameter(typeof(T));
return Expression.Lambda<Func<T, TValue>>(Expression.Property(obj, name), obj).Compile();
}
private static Action<T, TValue> BuildSetter<TValue>(string name)
{
var obj = Expression.Parameter(typeof(T));
var value = Expression.Parameter(typeof(TValue));
return Expression.Lambda<Action<T, TValue>>(Expression.Assign(Expression.Property(obj, name), value), obj, value).Compile();
}
public static void Init(T obj)
{
// Here's your custom initialization method
if (_getA(obj) == "Foo")
_setB(obj, 42);
else
_setC(obj, true);
}
}
Not necessarily the easiest one to grasp, but this should be much faster than using dynamic or reflection. That said, if you don't need the speed, stick with dynamic as it's easier.
I have the following abstract class:
public abstract class BaseClass{
public object contents { get; set; }
public Action<BaseClass> mutator;
public abstract void Initialise();
}
This will be used by several classes, which will override the Initialize method to assign a value to contents, which will in turn be mutated using the mutator delegate at specific points in time.
I have the following static class, with each method intended to be used as a mutator:
public static class Mutators{
public static void VariantA(A inputObj){
// inputObj.contents = something else
}
public static void VariantB(A inputObj) { } // etc. etc.
}
I then have class A, which implements BaseClass. I am trying to assign Mutators.VariantA to the mutator delegate, but i'm not able to.
public class A : BaseClass{
public A(){
mutator = Mutators.VariantA;
}
public override void Initialise(){
/* set the value of contents property here */
}
}
Specifically I get the following error: A method or delegateMutators.VariantA(A)' parameters do not match delegate System.Action<BaseClass>(BaseClass)' parameters (CS0123)
I understand that Mutators.VariantA(A) requires an object of type A, and the Action was declared to accept an input of type BaseClass, however as class A implements BaseClass I thought I would have been able to do this ?
Coming from dynamically typed languages i'm having a tough time getting to grips with working with types in this way :(
Is there any way I can point to a function with an input of the abstract type in this way ? Do I need to look at some other design pattern ?
Thanks
I understand that Mutators.VariantA(A) requires an object of type A, and the Action was declared to accept an input of type BaseClass, however as class A implements BaseClass I thought I would have been able to do this ?
Absolutely not.
An Action<BaseClass> has to be able to accept any BaseClass object. So for example, if your code were valid, I would be able to write:
Action<BaseClass> mutator = Mutators.VariantA;
mutator.Invoke(new B());
(Where B is another class derived from BaseClass.)
The fact that B derives from BaseClass makes it valid for the invocation - but it's not going to help your VariantA method work nicely.
It's not really clear why you have a mutator here - I strongly suspect you should abstract BaseClass from its mutations. I still don't follow what you're trying to achieve, but this design pattern isn't going to help you get there in a type-safe way.
You could write:
public abstract class BaseClass<T> where T : BaseClass<T> {
public object Contents { get; set; }
public Action<T> Mutator { get; set; }
public abstract void Initialise();
}
... then:
public class A : BaseClass<A> {
public A() {
Mutator = Mutators.VariantA;
}
}
... as then you'd be writing something which can mutate "A" values. But in my experience this sort of generic nesting gets really messy, really quickly.
I've used your current example and changed the Method Signature of one of the classes to the following and it works
public abstract class BaseClass
{
public object contents { get; set; }
public Action<BaseClass> mutator;
public abstract void Initialise();
}
public static class Mutators
{
public static void VariantA(BaseClass baseClass)
{
// inputObj.contents = something else
}
public static void VariantB(A inputObj) { } // etc. etc.
}
public class A : BaseClass
{
public A()
{
mutator = Mutators.VariantA;
}
public override void Initialise()
{
/* set the value of contents property here */
}
}
I have a series of objects, lets call them buildings, that each share certain properties that are static for that building, but different for each building, such as price. I assumed that the best way to implement this was to create an abstract superclass with the shared price attribute and set the values in each subclass, but I cannot figure out how to get this to work. Here is an example of something I have tried:
using System;
public abstract class Buildings
{
internal static int price;
internal static int turnsToMake;
}
using System;
public class Walls : Buildings
{
public Walls()
{
price = 200;
turnsToMake = 5;
}
}
This works fine for construction, but if I want to check the price before creating it (to check if the player has enough money) then it just returns a null value. I'm sure that it is is a super simple fix, but I can't figure it out. Any help?
There is a "patchy" yet simple solution that's worth to consider. If you define your base class as a Generic class, and in deriving classes set T as the class itself, It will work.
This happens because .NET statically defines a new type for each new definition.
For example:
class Base<T>
{
public static int Counter { get; set; }
public Base()
{
}
}
class DerivedA : Base<DerivedA>
{
public DerivedA()
{
}
}
class DerivedB : Base<DerivedB>
{
public DerivedB()
{
}
}
class Program
{
static void Main(string[] args)
{
DerivedA.Counter = 4;
DerivedB.Counter = 7;
Console.WriteLine(DerivedA.Counter.ToString()); // Prints 4
Console.WriteLine(DerivedB.Counter.ToString()); // Prints 7
Console.ReadLine();
}
}
Don't use static. Static says that all instances of Building have the same value. A derived class will not inherit its own copy of the statics; but would always modify the base class statics. In your design there would only be one value for price and turnsToMake.
This should work for you:
public abstract class Buildings
{
internal int price;
internal int turnsToMake;
}
However, most people don't like using fields these days and prefer properties.
public abstract class Buildings
{
internal int Price { get; set; }
internal int TurnsToMake { get; set; }
}
I want to check the price before creating it […]
I suppose that's how you got to static fields; however, static and virtual behaviour cannot be combined. That is, you would have to re-declare your static fields for each subclass. Otherwise, all your subclasses share the exact same fields and overwrite each others' values.
Another solution would be to use the Lazy<T, TMetadata> type from the .NET (4 or higher) framework class library:
public class Cost
{
public int Price { get; set; }
public int TurnsToMake { get; set; }
}
var lazyBuildings = new Lazy<Buildings, Cost>(
valueFactory: () => new Walls(),
metadata: new Cost { Price = 200, TurnsToMake = 5 });
if (lazyBuildings.Metadata.Price < …)
{
var buildings = lazyBuildings.Value;
}
That is, the metadata (.Metadata) now resides outside of the actual types (Buildings, Walls) and can be used to decide whether you actually want to build an instance ( .Value) of it.
(Thanks to polymorphism, you can have a whole collection of such "lazy factories" and find a building type to instantiate based on the metadata of each factory.)
Building on Uri Abramson's answer above:
If you need to access the static property from within the Base class, use reflection to get the value from T. Also, you can enforce that Base must be inherited using T of the derived type.
e.g.
class Base<T> where T : Base <T> {
static int GetPropertyValueFromDerivedClass<PropertyType>(BindingFlags Flags = BindingFlags.Public | BindingFlags.Static, [CallerMemberName] string PropertyName = "")
{
return typeof(T).GetProperty(PropertyName, Flags)?.GetValue(null);
}
static int Counter{ get => GetPropertyValueFromDerivedClass(); }
}
static int DoubleCounter{ return Counter*2; } //returns 8 for DerivedA and 14 for DerivedB
}
If you have a better way to do this, please post.
Not as easy for the inheritor, but workable...
public abstract class BaseType
{
public abstract contentType Data { get; set; }
}
public class InheritedType : BaseType
{
protected static contentType _inheritedTypeContent;
public override contentType Data { get => _inheritedTypeContent; set => _inheritedTypeContent = value; }
}
i have another question open here on SO and after thinking about it, i may be approaching this in the wrong way.
i have 4 classes, that have the same properties and methods.
some of the classes, have their own properties and methods ( not overrides of the existing ones ).
currently i create each class as:
public class ClassOne
{
public ClassOne()
{
}
public int ID {get;set;}
// More properties here
public void Set(){
// Do Stuff to save this
}
// More Methods here
}
cant i create one class that will generate all of the 4 classes?
and in the classes themselfs i only create specific properties/methods for that class?
repeating the code seems very odd to me, im sure there must be a way to do this, just dont know how.
Your situation is one of the main reasons why inheritance was invented. So with that, you can write
public class Base
{
// Properties and methods common to all
}
public class ClassOne : Base
{
// Properties and methods specific to ClassOne
}
public class ClassTwo : Base
{
// Properties and methods specific to ClassTwo
}
public class ClassThree : Base
{
// Properties and methods specific to ClassThree
}
public class ClassFour : Base
{
// Properties and methods specific to ClassFour
}
As requested, more code, using interfaces and abstract classes:
An interface is just a blueprint, defining what properties and methods are required to be compatible with other "BaseClasses"
public interface IBaseClass
{
public int ID {get;set;}
public void Set();
}
Abstract classes can contain code, but can not be instantiated, they are form of starting point for a class, but not a complete class themselves.
public abstract class ABaseClass : IBaseClass
{
public int ID {get;set;}
public void Set(){
// Do Stuff to save
}
}
Each class inherits from the abstract class and can then override and implement whatever it wants, customizing it however is necessary.
public class ClassOne : ABaseClass
{
}
public class ClassTwo : ABaseClass
{
}
public class ClassThree : ABaseClass
{
}
public class ClassFour : ABaseClass
{
}
ps. not entirely sure if my syntax is 100% correct
Could you simply make a base class with your properties and inherit from that class?
Why not use inheritance??
public class ClassOne
{
public ClassOne()
{
}
public virtual int ID {get;set;}
// More properties here
public virtual void Set(){
// Do Stuff to save this
}
// More Methods here }
public class ClassTwo : ClassOne
{
public string ClassTwoString { get; set; }
}
public class ClassThree : ClassOne
{
public string ClassThreeString { get; set; }
}
Can you make them all inherit off of the same class? If so, that sounds ideal.
Barring the possibility of making them inherit, you could write an interface that describes the methods and properties which each of them use. Then you can call each instance of the class through the same interface.
Barring again that possibility, you could write a reflective assignor/accessor. But you shouldn't do that.