Develop Reference

An issue with designing my interfaces in C# : Sample Project

I have a problem with designing my interfaces
I have these interfaces :
interface IField {
}
interface IScreenField : IField {
}
interface ITable {
CustomCollection<IField> CustomCollection { get; set; }
}
interface IScreen
{
AnotherCustomCollection<IScreenField> AnotherCustomCollection { get; set; }
}
IScreen interface should inherit from ITable but it shows an error that I have to implement a collection of IField but I already implement a collection of IScreenField
What is the soltuion for this ?
I uploaded a sample project to explain the issue more
You can check the error message in Screen class that says :
Screen does not implement interface member ITable.Fields. Screen.Fields cannot implement ITable.Fields becuase it does not have the matching return type of CusomCollection<IField>
Here is the sample :
Sample project

This description of this example helps you to solve the problem: If IExample2 inherits another Interface, when implementing IExample2 u need to implement
all the method(properties etc...) that has been declared in interface + the method of inhered interfaces from IExample2. Remember that when you implement an interface you have to implement all of members of that interface (you have to implement even the members of all interfaces that are in chain) and all the returns types has to be the same in interface and in class.
interface IExample
{
void Method1();
}
interface IExample2 : IExample
{
void Method2();
}
class Screen : IExample2
{
public void Method2()
{
}
public void Method1()
{
}
}
Chain Example
interface IExample
{
void Method1();
}
interface IExample2 : IExample
{
void Method2();
}
interface IExample3 : IExample2
{
void Method3();
}

This is the answer I posted on your previous post. Reposting it here as-is since your previous question was put on hold before I could
submit the answer.
It’s very difficult to identify the problem without looking at the full code but based on what you have said, I believe, you have implemented IScreenField explicitly and the compiler is not able to find any implementation of IField.
Checkout following for more info:
https://www.codeproject.com/Articles/1000374/Explicit-Interface-VS-Implicit-Interface-in-Csharp
Update: After looking at the code
First of all you need to understand difference between Implicit and Explicit implementations of an Interface:
Implicit: you access the interface properties and properties as if they were part of the class.
Explicit: you can only access properties and properties when treating the class as the implemented interface.
The problem with the Screen class is that it implements IScreen interface, which in-turn implements ITable interface. Both these interfaces have a property named Fields.
The problem surfaced due to this and you are required to
explicitly implement the Fields property in Screen class.
NOTE: It is irrelevant that you have different return types. Since you have implemented Fields property in both interfaces, it is assumed that you are expecting different values when the property is accessed from each of the interfaces.
public class Screen : IScreen
{
public string Name { get; set; }
AnotherCustomCollection<IBaseField> IScreen.Fields
{
get
{
return default(AnotherCustomCollection<IBaseField>);
}
}
CustomCollection<IField> ITable.Fields
{
get
{
return default(CustomCollection<IField>);
}
}
public string Title { get; set; }
public string Description { get; set; }
}
Now how to access them? To access Fields property of each of these Interfaces you need to access Screen object as those interfaces.
Ex:
var screen = new Screen();
var fields = screen.Fields; // Error
var fields = (screen as IScreen).Fields; // returns property value of IScreen Fields
var fields = (screen as ITable).Fields; // returns property value of ITable Fields
Here is the complete code: https://dotnetfiddle.net/5KS0Xd
Hope this was helpful. All the best and happy coding.

You could do something like this:
public class Screen : IScreen
{
public string Name { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public AnotherCustomCollection<IBaseField> Fields { get; set; }
CustomCollection<IField> ITable.Fields
{
get
{
throw new System.NotSupportedException();
}
}
}
And apparently the compiler likes that, and if you do something like this:
public static void Main(string[] args)
{
var collection = new List<IScreen>()
{
new Screen
{
Fields = new AnotherCustomCollection<ScreenInterface.IBaseField>
{
new TextField()
{
Name = "Hello"
}
}
}
};
var y = collection.First();
//Prints "Hello"
Console.WriteLine(string.Join(" ", y.Fields.Select(x => x.Name)));
Console.ReadLine();
}
But, if you are working with the upper interface (ITable)
public static void Main(string[] args)
{
var collection = new List<ITable>() //here
{
new Screen
{
Fields = new AnotherCustomCollection<ScreenInterface.IBaseField>
{
new TextField()
{
Name = "Hello"
}
}
}
};
var y = collection.First();
//Throws NotSupportedException
Console.WriteLine(string.Join(" ", y.Fields.Select(x => x.Name)));
Console.ReadLine();
}
My guess is that there isn't the concept of generic inheritance, and that may be proved if you switch the conditional generic parameter of AnotherCustomCollection from IBaseField to IField, and instead of throwing the exception, return the public Fields property on Screen.ITable.Fields. Compiler will automatically recognize the concrete property and everything will work.
So, for this to work, either define an implicit operator or a custom getter:
public class Screen : IScreen
{
public string Name { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public AnotherCustomCollection<IBaseField> Fields { get; set; }
CustomCollection<IField> ITable.Fields
{
get
{
var customCollection = new CustomCollection<IField>();
customCollection.AddRange(Fields);
return customCollection;
}
}
}

Type safety for passing in Types

Currently I am in the phase of refactoring my code after it has been unit tested, and I have some concerns about the refactoring from a design point of view with regards to type safety. My original code looked a bit like this:
Interfaces
public interface IBase
{
int ID { get; set; }
}
public interface IFirstSub : IBase
{
string Description { get; set; }
}
public interface ISecondSub : IBase
{
decimal Total { get; set; }
}
public interface IThirdSub : IBase
{
int Count { get; set; }
}
public interface IBaseContainer
{
void Add(IBase baseParam);
}
Implementations
public class FirstContainer : IBaseContainer
{
public void Add(IBase baseParam)
{
if (!(baseParam is IFirstSub || baseParam is ISecondSub))
{
throw new ArgumentException(nameof(baseParam));
}
// Do Something
}
}
public class SecondContainer : IBaseContainer
{
public void Add(IBase baseParam)
{
if (!(baseParam is IThirdSub))
{
throw new ArgumentException(nameof(baseParam));
}
// Do Something
}
}
With my original implementation of FirstContainer and SecondContainer, it was repeating the same logic at the start of the Add method, so I thought I would refactor the code to look something like this:
public abstract class BaseContainer : IBaseContainer
{
private readonly List<Type> _types = new List<Type>();
protected BaseContainer(params Type[] baseTypes)
{
_types.AddRange(baseTypes);
}
public void Add(IBase baseParam)
{
if (_types.All(type => !type.IsInstanceOfType(baseParam)))
{
throw new ArgumentException(nameof(baseParam));
}
DoSomething(baseParam);
}
protected abstract void DoSomething(IBase baseParam);
}
public class ThirdContainer : BaseContainer
{
public ThirdContainer() : base(typeof(IFirstSub)) { }
protected override void DoSomething(IBase baseParam)
{
// Do Something
}
}
With this refactoring done, it successfully removes the duplication of the code from the start of the Add method, but my main concern with the refactoring is the fact that the call to the base constructor base(typeof(IFirstSub)) is not really type safe. By that, I mean I can call the base constructor like base(typeof(object)) for example, and it will compile. For the purposes of my project, I'd like to constrain the types to ones that inherit IBase, and enforce at compile time.
Is there anyway to overcome this limitation, or would a new design be needed in order to achieve this?

No it's not type safe
Passing and validating types at run-time is not type-safe, as type-safety is a compile-time concept. In my opinion your refactoring effort does not improve the code, and in fact does something quite weird.
Function overloading
If you need a method that accepts either of two types, you can use function overloading:
public class FirstContainer : IBaseContainer
{
public void Add(IFirstSub param)
{
// Do Something
}
public void Add(ISecondSub param)
{
// Do Something
}
}
The compiler will automatically choose the right prototype for you, and will not allow anything other than an IFirstSub or ISecondSub.
Create another interface
Another approach requires you to add an interface for the types that have something in common, like this:
interface ICanBeHeldInFirstContainer
{ }
public interface IFirstSub : IBase, ICanBeHeldInFirstContainer
{
string Description { get; set; }
}
public interface ISecondSub : IBase, ICanBeHeldInFirstContainer
{
decimal Total { get; set; }
}
Then you do this:
public class FirstContainer : IBaseContainer
{
public void Add(ICanBeHeldInFirstContainer param)
{
// Do Something
}
}
or this:
public class FirstContainer : IBaseContainer
{
public void Add<T>(T param) where T : ICanBeHeldInFirstContainer
{
// Do Something
}
}

Generic objects in c#

i have a litte problem and i need some help :)
For example i have a simle abstract class
public abstract class BaseDefinition
{
public int Id { get;set; }
public string Name { get;set; }
}
and other base class
public abstract class BaseParentClass
{
public string Name { get;set; }
public string Schema { get;set; }
}
and first generic abstract class
public abstrac class BaseParentClass<T> :
BaseParentClass where T : BaseDefinition
{
public IList<T> Objects {get;set;}
}
and first implementations
public class ClassADefintion : BaseDefinition
{
public bool IsChanged {get;set;}
}
public class ClassAObject : BaseParentClass<ClassADefinition>
{
public bool OtherField {get;set;}
}
public class ClassBDefintion : BaseDefinition
{
public bool IsBBBChanged {get;set;}
}
public class ClassBObject : BaseParentClass<ClassBDefinition>
{
public bool OtherBBBBField {get;set;}
}
Sorry for class name, but I can't create anything better (it's only example)
As We see, now is all OK :).
I have some methods who returns a IEnumerable of generic implementation
IEnumerable<ClassBObject> ClassBObjectCollection;
IEnumerable<ClassAObject> ClassAObjectCollection;
Now i must create a method, who can take a generic objects in IEnumerable
public void DoWork(IEnumerable<BaseParentClass<BaseDefinition>> objects)
{
foreach(var baseObj in objects)
{
foreach(var baseDef in baseObj.Objects)
{
// do some work
}
}
}
How i remember BaseObject<BaseDefinition> != ClassAObject, but compiler doesn't put on screen any errors. I remember in .NET in generic interface We can use IN and OUT T, so i try make this
public interface IBaseParentClass<out T> where T : BaseDefinition
{
IList<T> Objects {get;set;}
}
Yup, You can't make a List of <out T>. Somebody have any idea for this problem ?
I can get this fields values by reflection, but i have abstract class and interface so i think is a better way.

I don't have a compiler at hand, but I think it should be possible to rewrite DoWork as such:
public void DoWork<T>(IEnumerable<BaseObject<T>> objects)
where T : BaseDefinition
{
foreach(var baseObj in objects)
{
foreach(var baseDef in baseObj.Objects)
{
// do some work
}
}
}
I am not sure whether the compiler will be able to infer T for you, try it out.
Another possibility may be that if you enumerate those objects anyway, to make Objects of Type IEnumerable(Of T).

No base class problem, How to use Castle.DynamicProxy Mixin in this particular case?

I have a 3rd party badly designed library that I must use.
It has all sorts of types it works with, we'll call them SomeType1, SomeType2 etc.
None of those types share a common base class but all have a property named Value with a different return type.
All I want to do is to be able to Mixin this class so I'll be able to call someType1Instance.Value and someType2Instance.Value without caring what the concreate type it is and without caring what the return type is (I can use object).
So my code is currently:
public interface ISomeType<V>
{
V Value {get; set;}
}
public interface ISomeTypeWrapper
{
object Value { get; set; }
}
public class SomeTypeWrapper<T> : ISomeTypeWrapper
where T : ISomeType<???>
{
T someType;
public SomeTypeWrapper(T wrappedSomeType)
{
someType = wrappedSomeType
}
public object Value
{
get { return someType.Value; }
set { someType.Value = value != null ? value : default(T); }
}
}
public class SomeType1
{
public int Value { get; set; }
}
public class SomeType2
{
public string Value { get; set; }
}
The problem is that I don't know what T might be until runtime due to the fact that I get a dictionary of objects.
I can iterate the dictionary and use reflection to create a SomeWrapperType on runtime but I would like to avoid it.
How can I mixin the concreate type of SomeType to ISomeType?
How can I know what V type parameter is? (wish I had typedefs and decltype like in c++)
How can I, with the minimum of use of reflection possible Mixin those classes with the interface/base class?

You could try the Duck Typing Extensions for Windsor. It means you will need to register each of your types.
container
.Register(Component.For(typeof(SomeType1)).Duck<ISomeType>())
.Register(Component.For(typeof(SomeType2)).Duck<ISomeType>());
You could probably use linq and the register AllTypes syntax to reduce code if the names are similar.
Alternatively in the short term create a factory which can return you the objects you need, implement a concrete object for each type. No you are using the interface you can remove the factory at a later date and replace it with something else with minimal impact:
public class SomeTypeWrapperFactory
{
public ISomeType<int> CreateWrapper(SomeType1 someType1)
{
return new SomeType1Wrapper(someType1);
}
public ISomeType<string> CreateWrapper(SomeType2 someType2)
{
return new SomeType2Wrapper(someType2);
}
}
public class SomeType1Wrapper : ISomeType<int> { ... }
public class SomeType2Wrapper : ISomeType<int> { ... }
Regardless of how you implement the wrapper, be the individually or using a god like class you have the ability to change how the wrapping is done and keep the rest of your code clean.

Why SomeTypeWrapper but not SomeObjectWrapper?
public class SomeObjectWrapper : ISomeType
{
Object _someObject;
PropertyInfo _valuePropertyInfo;
public SomeObjectWrapper(Object wrappedSomeObject)
{
_someObject = wrappedSomeObject;
_valuePropertyInfo = _someObject.GetType().GetProperty("Value", System.Reflection.BindingFlags.Public);
}
public object Value
{
get { return _valuePropertyInfo.GetValue(_someObject, null); }
set { _valuePropertyInfo.SetValue(_someObject, value, null); }
}
}

Edited With .NET 3.5 using LinFu
You may use LinFu instead of Castle. However, you would be using reflection anyway, both with Castle's and with Linfu's DynamicProxy, only hidden in the guts of the libraries instead of being exposed in your code. So if your requirement to avoid the use of reflection is out of performance concerns, you wouldn't really avoid it with this solution.
In that case I would personally choose Orsol's solution.
However: here's an example with LinFu's ducktyping.
public interface ISomeType {
object Value{get; set;}
}
public class SomeType1
{
public int Value { get; set; }
}
public class SomeType2
{
public string Value { get; set; }
}
public class SomeTypeWrapperFactory
{
public static ISomeType CreateSomeTypeWrapper(object aSomeType)
{
return aSomeType.CreateDuck<ISomeType>();
}
}
class Program
{
public static void Main(string[] args)
{
var someTypes = new object[] {
new SomeType1() {Value=1},
new SomeType2() {Value="test"}
};
foreach(var o in someTypes)
{
Console.WriteLine(SomeTypeWrapperFactory.CreateSomeTypeWrapper(o).Value);
}
Console.ReadLine();
}
}
Since you don't know the type of the SomeType's until runtime, I would not use mixins, but the visitor pattern (I know this doesn't answer the question on how to use mixins for this, but I just thought I'd throw in my 2 cents).
With .NET 4 using dynamic
See Bradley Grainger's post here on using c#4's dynamic keyword to implement the visitor pattern.
In your case, reading all the "Value" properties from your dictionary of SomeType's could work like this:
public class SomeType1
{
public int Value { get; set; }
}
public class SomeType2
{
public string Value { get; set; }
}
public class SomeTypeVisitor
{
public void VisitAll(object[] someTypes)
{
foreach(var o in someTypes) {
// this should be in a try-catch block
Console.WriteLine(((dynamic) o).Value);
}
}
}
class Program
{
public static void Main(string[] args)
{
var someTypes = new object[] {
new SomeType1() {Value=1},
new SomeType2() {Value="test"}
};
var vis = new SomeTypeVisitor();
vis.VisitAll(someTypes);
}
}

Calling Generic Property In Generic Class From Interface Implemented By Generic Class

I have a generic class that has one type parameter (T). I needed to store a collection of these generic objects that are of different types, so I created an interface that the generic class implements as suggested here. There is a property in the generic class of type T that I need to access when iterating through the generic list that contains the collection of Interface objects. So far the only way I have been able to get the value is to call a method using reflection.
interface ISomeClass {
//?
}
class SomeClass<T> : ISomeClass {
T ValueINeed { get; set;}
}
class ClassThatHasListOfGenericObjects{
List<ISomeClass> _l = new List<ISomeClass>();
public AddToList<T>(T someClass) : where T : ISomeClass {
_l.Add(someClass);
}
public SomeMethod(){
foreach(ISomeClass i in _l){
i.ValueINeed; //I don't know how to access the property in the generic class
}
}
}

As I see it you have two options. The easy option is to expose the value (as an object) on the interface (and possibly its type as well). Here's how that would look:
interface ISomeClass
{
object ValueINeed { get; set; }
// Only needed if you care about static type rather than using ValueINeed.GetType()
Type TypeOfValue { get; }
}
class SomeClass<T> : ISomeClass
{
public T ValueINeed { get; set; }
public Type TypeOfValue { get { return typeof(T); } }
object ISomeClass.ValueINeed { get { return ValueINeed; } set { ValueINeed = (T)value; } }
}
This has the disadvantage that there's a bit of casting going on and you might need to invoke reflection to do certain things with the value. It has the advantage that it's easy to understand and implement.
The other alternative would be to encode an "existential type" which truly represents a SomeClass<T> for some unknown T (like a SomeClass<?> in Java). This is much more complicated and hard to follow, but avoids any casts:
interface ISomeClassUser<X>
{
X Use<T>(SomeClass<T> s);
}
interface ISomeClassUser
{
void Use<T>(SomeClass<T> s);
}
interface ISomeClass
{
X Apply<X>(ISomeClassUser<X> user);
void Apply(ISomeClassUser user);
}
class SomeClass<T> : ISomeClass
{
public T ValueINeed { get; set; }
public X Apply<X>(ISomeClassUser<X> user) { return user.Use(this); }
public void Apply(ISomeClassUser user) { user.Use(this); }
}
// Assumes you want to get a string out, use a different generic type as needed
class XmlUser : ISomeClassUser<string>
{
public string Use<T>(SomeClass<T> s)
{
string str = "";
// do your conditional formatting here, branching on T as needed
// ...
return str;
}
}
class ClassThatHasListOfGenericObjects
{
List<ISomeClass> _l = new List<ISomeClass>();
XmlUser user = new XmlUser();
public string SomeMethod()
{
string s = "";
foreach (ISomeClass i in _l)
{
s += i.Apply(user);
}
return s;
}
}

Add ValueINeed to the interface and you'll be able to call it in SomeMethod().

I think you might just need a little refactoring. Looks like you're almost there
interface ISomeClass<T> {
T ValueINeed { get; set; }
}
class SomeClass<T> : ISomeClass {
T ValueINeed { get; set;}
}
class ClassThatHasListOfGenericObjects{
List<ISomeClass> _l = new List<ISomeClass>();
public AddToList<T>(T someClass) : where T : ISomeClass {
_l.Add(someClass);
}
public SomeMethod(){
foreach(ISomeClass i in _l){
i.ValueINeed; //this will work now, since it's in the interface
}
}
}

The elements' types you are using is of ISomeClass, so if want to access a member property you need to either cast i to SomeClass or add the property deceleration to the interface
interface ISomeClass {
T ValueNeeded
{
get;
set;
}
}
Note that you still need to implement the property in SomeClass.