I want to be able to use the method RaiseMessage that exists on the Abstract Class AgentBase, on other classes through the program.
public class MNyTestAgent: AgentBase
{
RaiseMessage("hey", "hey")
var a = new Foo();
}
public class Foo
{
public Foo()
{
RaiseMessage("","") -<< how do i use it here
}
}
First of all, your code isn't valid C#.
Second of all, if you want to have a method accessible everywhere else, you probably want a public static. To implement a public static method you need to first reconsider your life choices, as doing so in an Agent class looks like bad design and a violation of OOP principles. If you still decide that you need it, something like this should work:
public abstract class AgentBase
{
public static RaiseMessage(string title, string message)
{
// Implementation.
}
}
public class MNyTestAgent: AgentBase
{
public MNyTestAgent()
{
AgentBase.RaiseMessage("hey", "hey");
}
}
public class Foo
{
public Foo()
{
AgentBase.RaiseMessage("hey", "hey");
}
}
Could maybe this help?
public class MNyTestAgent: AgentBase
{
RaiseMessage('hey', 'hey')
var a = new Foo(this);
}
public class Foo
{
public Foo()
{
}
public Foo(AgentBase base)
{
base.RaiseMessage('','') -<< how do i use it here
}
}
Basically I have a class with a private method and lots of public methods that call this private method. I want to group these public methods logically (preferably to separate files) so it'll be organized, easier to use and maintain.
public class MainClass
{
private void Process(string message)
{
// ...
}
public void MethodA1(string text)
{
string msg = "aaa" + text;
Process(msg);
}
public void MethodA2(int no)
{
string msg = "aaaaa" + no;
Process(msg);
}
public void MethodB(string text)
{
string msg = "bb" + text;
Process(msg);
}
// lots of similar methods here
}
Right now I'm calling them like this:
MainClass myMainClass = new MainClass();
myMainClass.MethodA1("x");
myMainClass.MethodA2(5);
myMainClass.MethodB("y");
I want to be able to call them like this:
myMainClass.A.Method1("x");
myMainClass.A.Method2(5);
myMainClass.B.Method("y");
How can I achieve it? There is probably an easy way that I'm not aware of.
You're looking for object composition.
In computer science, object composition (not to be confused with
function composition) is a way to combine simple objects or data types
into more complex ones.
BTW, you shouldn't think that such refactor is grouping methods logically: it's just you need to implement your code with a clear separation of concerns:
In computer science, separation of concerns (SoC) is a design
principle for separating a computer program into distinct sections,
such that each section addresses a separate concern.
Practical example:
public class A
{
// B is associated with A
public B B { get; set; }
}
public class B
{
public void DoStuff()
{
}
}
A a = new A();
a.B = new B();
a.B.DoStuff();
You may move methods to separate classes. Classes may be new classes with dependency to MainClass with public/internal Process method, nested in MainClass or inherited from MainClass. Example with inheritance:
public class MainClass
{
protected void Process(string message)
{
// ...
}
}
public class A: MainClass
{
// methods for A go here
}
public class B: MainClass
{
// methods for B go here
}
You can use nested classes:
public class MainClass
{
// private method here
public class A
{
// methods for A go here
}
public class B
{
// methods for B go here
}
}
If you want them in different files, you can use a partial class for MainClass
// file 1
public partial class MainClass
{
public class A { }
}
// file 2
public partial class MainClass
{
public class B { }
}
I want to do something like this:
public class MyClass {
public virtual void Foo() {
this.DoSomethingThatWouldBeFineInASubclassButAnOverrideWouldNotWantToUse();
}
}
Basically, I am doing some work here, and I want a default way of doing it, but if someone is going to override, they should likely NOT be using the default. It is so easy to put base.Foo() into an override without thinking about it; in fact my IDE does it automatically. I want to prevent that. Is it possible?
This is better solved with composition instead of inheritance. Perhaps, using the strategy pattern:
interface ISomeStrategy
{
void Do();
}
public class MyClass {
private readonly ISomeStrategy _strategy;
public MyClass() : this(null) {}
public MyClass(ISomeStrategy strategy)
{
// the default implementation and the user-defined implementation
// are mutually exclusive
_strategy = strategy ?? new DefaultStrategy();
}
public void Foo()
{
_strategy.Do();
}
//secret strategy
private class DefaultStrategy : ISomeStrategy
{
public void Do()
{
//secret implementation
}
}
}
Subclassing:
public class Derived : MyClass
{
public Derived() : base(new DerivedStrategy())
{
}
}
A bit more verbose, but effective.
In my console application have an abstract Factory class "Listener" which contains code for listening and accepting connections, and spawning client classes. This class is inherited by two more classes (WorldListener, and MasterListener) that contain more protocol specific overrides and functions.
I also have a helper class (ConsoleWrapper) which encapsulates and extends System.Console, containing methods for writing to console info on what is happening to instances of the WorldListener and MasterListener.
I need a way to determine in the abstract ListenerClass which Inheriting class is calling its methods.
Any help with this problem would be greatly appreciated! I am stumped :X
Simplified example of what I am trying to do.
abstract class Listener
{
public void DoSomething()
{
if(inheriting class == WorldListener)
ConsoleWrapper.WorldWrite("Did something!");
if(inheriting class == MasterListener)
ConsoleWrapper.MasterWrite("Did something!");
}
}
public static ConsoleWrapper
{
public void WorldWrite(string input)
{
System.Console.WriteLine("[World] {0}", input);
}
}
public class WorldListener : Listener
{
public void DoSomethingSpecific()
{
ConsoleWrapper.WorldWrite("I did something specific!");
}
}
public void Main()
{
new WorldListener();
new MasterListener();
}
Expected output
[World] Did something!
[World] I did something specific!
[Master] Did something!
[World] I did something specific!
If you know each of the types you want to compare against, then use the is operator:
if (this is WorldListener)
{
// ...
}
else if (this is MasterListener)
{
// ...
}
Alternatively, you could use GetType if you want a little more flexibility:
var type = GetType();
// Do some logic on the type to determine what to do next.
You should be careful with this approach, however; it's generally indicative of bad design that you need to explicitly check for types (as these lovely people insist). Instead, it's almost always more appropriate to use polymorphism to delegate the desired behaviour to the base class (using a virtual or abstract method in the base class) – this is, after all, what it's designed for!
You might apply polymorphism something like this:
static class Program
{
static void Main(string[] args)
{
Listener listener = new WorldListener();
listener.DoSomething();
}
}
abstract class Listener
{
public void DoSomething()
{
var output = Decorate("Did something!");
ConsoleWrapper.WriteLine(output);
}
protected abstract string Decorate(string input);
}
class WorldListener : Listener
{
protected override string Decorate(string input)
{
return string.Format("[World] {0}", input);
}
}
class MasterListener : Listener
{
protected override string Decorate(string input)
{
return string.Format("[Master] {0}", input);
}
}
This will produce the output [World] Did something!. The advantage of this approach is that if you ever want to add another type of listener, it's simply a matter of defining a new class for it with the appropriate Decorate method; there's no need to modify Listener itself.
You can use
if (this is WorldListener)
instead of your pseudocode
if (inheriting class == WorldListener)
However, doing this is a bad design smell. You should strongly consider an alternative solution, e.g. performing the write to the console wrapper in a virtual method instead of adding this strong coupling between the base class and its subclasses.
Hmm.. Well, in your simplified example you don't call DoSomething() and DoSomethingSpecific(), and there's no implementation for MasterListener..
Also, if I understand it right, in your expected output your MasterListener.DoSomethingSpecific() runs a ConsoleWrapper.WorldWrite.. You probably meanr MasterWrite?
In any case.. Here's a working example that does what you want (at least in the way I understood your request :P )
The printed result is:
[World] Did something
[World] I did sth specific!
[Master] Did something
[Master] I did sth specific!
The code:
void Main()
{
var wl = new WorldListener();
wl.DoSomething();
wl.DoSpecific();
var ml = new MasterListener();
ml.DoSomething();
ml.DoSpecific();
}
public abstract class Listener
{
public abstract string Category { get; }
public void DoSomething()
{
ConsoleWrapper.Write(Category, "Did something");
}
}
public static class ConsoleWrapper
{
public static void Write(string category, string input)
{
Console.WriteLine("[{0}] {1}", category, input);
}
}
public class WorldListener : Listener
{
public override string Category { get { return "World"; } }
public void DoSpecific()
{
ConsoleWrapper.Write(Category, "I did sth specific!");
}
}
public class MasterListener : Listener
{
public override string Category { get { return "Master"; } }
public void DoSpecific()
{
ConsoleWrapper.Write(Category, "I did sth specific!");
}
}
Recently I've been thinking about securing some of my code. I'm curious how one could make sure an object can never be created directly, but only via some method of a factory class. Let us say I have some "business object" class and I want to make sure any instance of this class will have a valid internal state. In order to achieve this I will need to perform some check before creating an object, probably in its constructor. This is all okay until I decide I want to make this check be a part of the business logic. So, how can I arrange for a business object to be creatable only through some method in my business logic class but never directly? The first natural desire to use a good old "friend" keyword of C++ will fall short with C#. So we need other options...
Let's try some example:
public MyBusinessObjectClass
{
public string MyProperty { get; private set; }
public MyBusinessObjectClass (string myProperty)
{
MyProperty = myProperty;
}
}
public MyBusinessLogicClass
{
public MyBusinessObjectClass CreateBusinessObject (string myProperty)
{
// Perform some check on myProperty
if (true /* check is okay */)
return new MyBusinessObjectClass (myProperty);
return null;
}
}
It's all okay until you remember you can still create MyBusinessObjectClass instance directly, without checking the input. I would like to exclude that technical possibility altogether.
So, what does the community think about this?
You can make the constructor private, and the factory a nested type:
public class BusinessObject
{
private BusinessObject(string property)
{
}
public class Factory
{
public static BusinessObject CreateBusinessObject(string property)
{
return new BusinessObject(property);
}
}
}
This works because nested types have access to the private members of their enclosing types. I know it's a bit restrictive, but hopefully it'll help...
Looks like you just want to run some business logic before creating the object - so why dont you just create a static method inside the "BusinessClass" that does all the dirty "myProperty" checking work, and make the constructor private?
public BusinessClass
{
public string MyProperty { get; private set; }
private BusinessClass()
{
}
private BusinessClass(string myProperty)
{
MyProperty = myProperty;
}
public static BusinessClass CreateObject(string myProperty)
{
// Perform some check on myProperty
if (/* all ok */)
return new BusinessClass(myProperty);
return null;
}
}
Calling it would be pretty straightforward:
BusinessClass objBusiness = BusinessClass.CreateObject(someProperty);
Or, if you want to go really fancy, invert control: Have the class return the factory, and instrument the factory with a delegate that can create the class.
public class BusinessObject
{
public static BusinessObjectFactory GetFactory()
{
return new BusinessObjectFactory (p => new BusinessObject (p));
}
private BusinessObject(string property)
{
}
}
public class BusinessObjectFactory
{
private Func<string, BusinessObject> _ctorCaller;
public BusinessObjectFactory (Func<string, BusinessObject> ctorCaller)
{
_ctorCaller = ctorCaller;
}
public BusinessObject CreateBusinessObject(string myProperty)
{
if (...)
return _ctorCaller (myProperty);
else
return null;
}
}
:)
You could make the constructor on your MyBusinessObjectClass class internal, and move it and the factory into their own assembly. Now only the factory should be able to construct an instance of the class.
After so many years this got asked, and all the answers I see are unfortunately telling you how you should do your code instead of giving a straight answer. The actual answer you were looking for is having your classes with a private constructor but a public instantiator, meaning that you can only create new instances from other existing instances... that are only available in the factory:
The interface for your classes:
public interface FactoryObject
{
FactoryObject Instantiate();
}
Your class:
public class YourClass : FactoryObject
{
static YourClass()
{
Factory.RegisterType(new YourClass());
}
private YourClass() {}
FactoryObject FactoryObject.Instantiate()
{
return new YourClass();
}
}
And, finally, the factory:
public static class Factory
{
private static List<FactoryObject> knownObjects = new List<FactoryObject>();
public static void RegisterType(FactoryObject obj)
{
knownObjects.Add(obj);
}
public static T Instantiate<T>() where T : FactoryObject
{
var knownObject = knownObjects.Where(x => x.GetType() == typeof(T));
return (T)knownObject.Instantiate();
}
}
Then you can easily modify this code if you need extra parameters for the instantiation or to preprocess the instances you create. And this code will allow you to force the instantiation through the factory as the class constructor is private.
Apart from what Jon suggested, you could also either have the factory method (including the check) be a static method of BusinessObject in the first place. Then, have the constructor private, and everyone else will be forced to use the static method.
public class BusinessObject
{
public static Create (string myProperty)
{
if (...)
return new BusinessObject (myProperty);
else
return null;
}
}
But the real question is - why do you have this requirement? Is it acceptable to move the factory or the factory method into the class?
Yet another (lightweight) option is to make a static factory method in the BusinessObject class and keep the constructor private.
public class BusinessObject
{
public static BusinessObject NewBusinessObject(string property)
{
return new BusinessObject();
}
private BusinessObject()
{
}
}
So, it looks like what I want cannot be done in a "pure" way. It's always some kind of "call back" to the logic class.
Maybe I could do it in a simple way, just make a contructor method in the object class first call the logic class to check the input?
public MyBusinessObjectClass
{
public string MyProperty { get; private set; }
private MyBusinessObjectClass (string myProperty)
{
MyProperty = myProperty;
}
pubilc static MyBusinessObjectClass CreateInstance (string myProperty)
{
if (MyBusinessLogicClass.ValidateBusinessObject (myProperty)) return new MyBusinessObjectClass (myProperty);
return null;
}
}
public MyBusinessLogicClass
{
public static bool ValidateBusinessObject (string myProperty)
{
// Perform some check on myProperty
return CheckResult;
}
}
This way, the business object is not creatable directly and the public check method in business logic will do no harm either.
In a case of good separation between interfaces and implementations the
protected-constructor-public-initializer pattern allows a very neat solution.
Given a business object:
public interface IBusinessObject { }
class BusinessObject : IBusinessObject
{
public static IBusinessObject New()
{
return new BusinessObject();
}
protected BusinessObject()
{ ... }
}
and a business factory:
public interface IBusinessFactory { }
class BusinessFactory : IBusinessFactory
{
public static IBusinessFactory New()
{
return new BusinessFactory();
}
protected BusinessFactory()
{ ... }
}
the following change to BusinessObject.New() initializer gives the solution:
class BusinessObject : IBusinessObject
{
public static IBusinessObject New(BusinessFactory factory)
{ ... }
...
}
Here a reference to concrete business factory is needed to call the BusinessObject.New() initializer. But the only one who has the required reference is business factory itself.
We got what we wanted: the only one who can create BusinessObject is BusinessFactory.
public class HandlerFactory: Handler
{
public IHandler GetHandler()
{
return base.CreateMe();
}
}
public interface IHandler
{
void DoWork();
}
public class Handler : IHandler
{
public void DoWork()
{
Console.WriteLine("hander doing work");
}
protected IHandler CreateMe()
{
return new Handler();
}
protected Handler(){}
}
public static void Main(string[] args)
{
// Handler handler = new Handler(); - this will error out!
var factory = new HandlerFactory();
var handler = factory.GetHandler();
handler.DoWork(); // this works!
}
I don't understand why you want to separate the "business logic" from the "business object". This sounds like a distortion of object orientation, and you'll end up tying yourself in knots by taking that approach.
I'd put the factory in the same assembly as the domain class, and mark the domain class's constructor internal. This way any class in your domain may be able to create an instance, but you trust yourself not to, right? Anyone writing code outside of the domain layer will have to use your factory.
public class Person
{
internal Person()
{
}
}
public class PersonFactory
{
public Person Create()
{
return new Person();
}
}
However, I must question your approach :-)
I think that if you want your Person class to be valid upon creation you must put the code in the constructor.
public class Person
{
public Person(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
Validate();
}
}
This solution is based off munificents idea of using a token in the constructor. Done in this answer make sure object only created by factory (C#)
public class BusinessObject
{
public BusinessObject(object instantiator)
{
if (instantiator.GetType() != typeof(Factory))
throw new ArgumentException("Instantiator class must be Factory");
}
}
public class Factory
{
public BusinessObject CreateBusinessObject()
{
return new BusinessObject(this);
}
}
Multiple approaches with different tradeoffs have been mentioned.
Nesting the factory class in the privately constructed class only allows the factory to construct 1 class. At that point you're better off with a Create method and a private ctor.
Using inheritance and a protected ctor has the same issue.
I'd like to propose the factory as a partial class that contains private nested classes with public constructors. You're 100% hiding the object your factory is constructing and only exposing what you choose to through one or multiple interfaces.
The use case I heard for this would be when you want to track 100% of instances in the factory. This design guarantees no one but the factory has access to creating instances of "chemicals" defined in the "factory" and it removes the need for a separate assembly to achieve that.
== ChemicalFactory.cs ==
partial class ChemicalFactory {
private ChemicalFactory() {}
public interface IChemical {
int AtomicNumber { get; }
}
public static IChemical CreateOxygen() {
return new Oxygen();
}
}
== Oxygen.cs ==
partial class ChemicalFactory {
private class Oxygen : IChemical {
public Oxygen() {
AtomicNumber = 8;
}
public int AtomicNumber { get; }
}
}
== Program.cs ==
class Program {
static void Main(string[] args) {
var ox = ChemicalFactory.CreateOxygen();
Console.WriteLine(ox.AtomicNumber);
}
}
I don't think there is a solution that's not worse than the problem , all he above require a public static factory which IMHO is a worse problem and wont stop people just calling the factory to use your object - it doesnt hide anything . Best to expose an interface and/or keep the constructor as internal if you can that's the best protection since the assembly is trusted code.
One option is to have a static constructor which registers a factory somewhere with something like an IOC container.
Here is another solution in the vein of "just because you can doesn't mean you should" ...
It does meet the requirements of keeping the business object constructor private and putting the factory logic in another class. After that it gets a bit sketchy.
The factory class has a static method for creating business objects. It derives from the business object class in order to access a static protected construction method that invokes the private constructor.
The factory is abstract so you can't actually create an instance of it (because it would also be a business object, so that would be weird), and it has a private constructor so client code can't derive from it.
What's not prevented is client code also deriving from the business object class and calling the protected (but unvalidated) static construction method. Or worse, calling the protected default constructor we had to add to get the factory class to compile in the first place. (Which incidentally is likely to be a problem with any pattern that separates the factory class from the business object class.)
I'm not trying to suggest anyone in their right mind should do something like this, but it was an interesting exercise. FWIW, my preferred solution would be to use an internal constructor and the assembly boundary as the guard.
using System;
public class MyBusinessObjectClass
{
public string MyProperty { get; private set; }
private MyBusinessObjectClass(string myProperty)
{
MyProperty = myProperty;
}
// Need accesible default constructor, or else MyBusinessObjectFactory declaration will generate:
// error CS0122: 'MyBusinessObjectClass.MyBusinessObjectClass(string)' is inaccessible due to its protection level
protected MyBusinessObjectClass()
{
}
protected static MyBusinessObjectClass Construct(string myProperty)
{
return new MyBusinessObjectClass(myProperty);
}
}
public abstract class MyBusinessObjectFactory : MyBusinessObjectClass
{
public static MyBusinessObjectClass CreateBusinessObject(string myProperty)
{
// Perform some check on myProperty
if (true /* check is okay */)
return Construct(myProperty);
return null;
}
private MyBusinessObjectFactory()
{
}
}
Would appreciate hearing some thoughts on this solution.
The only one able to create 'MyClassPrivilegeKey' is the factory. and 'MyClass' requires it in the constructor.
Thus avoiding reflection on private contractors / "registration" to the factory.
public static class Runnable
{
public static void Run()
{
MyClass myClass = MyClassPrivilegeKey.MyClassFactory.GetInstance();
}
}
public abstract class MyClass
{
public MyClass(MyClassPrivilegeKey key) { }
}
public class MyClassA : MyClass
{
public MyClassA(MyClassPrivilegeKey key) : base(key) { }
}
public class MyClassB : MyClass
{
public MyClassB(MyClassPrivilegeKey key) : base(key) { }
}
public class MyClassPrivilegeKey
{
private MyClassPrivilegeKey()
{
}
public static class MyClassFactory
{
private static MyClassPrivilegeKey key = new MyClassPrivilegeKey();
public static MyClass GetInstance()
{
if (/* some things == */true)
{
return new MyClassA(key);
}
else
{
return new MyClassB(key);
}
}
}
}