expose a referenced type (class) without need for additional reference

Question

I have a layered system of .dlls between my application, where the lowest level has a class that provides certain functionality - an instance of this class can be received through a GetClass() function and then I can access its properties (basically, a collection of information of changing objects).

Now I noticed that when I want to access that information from the next higher level .dll, the compiler complains that I do not have the lower level .dll referenced (the one defining the class) - which actually I would want to avoid, to have a nice layered structure in my architecture.

How to get around this? Can I re-expose the referenced type? Do I really have to write a wrapper of my own, if I want exactly the same functionality? Or do I even need to reference the low level .dll again?

DLL 1:

class myClass;
myClass GetMyClass();

DLL 2:

myClass GetMyClass();

EXE:

How to access result from calling GetMyClass (DLL 2) without referencing DLL 1?

Answer 1

You need to separate all the common classes you use across all your layers into a new dll, then reference this dll on every project.

Try to use interfaces so you can work over the contract (the functionality) instead of the concrete implementation. It will help you to avoid unnecessary references.

// common dll
public interface IMyClass
{
    string MyData { get; set; }
    IMyClass GetMyClass();
}

// dll1
public class myClass : IMyClass
{
    public string MyData { get; set; }
    public IMyClass GetMyClass() { return new myClass() { MyData = "abc" }; }
}

// dll2
public class myClass2
{
    public IMyClass GetMyClass()
    {
         var c1 = new myClass();
         var c2 = c1.GetMyClass();
         return c2;
    }
}

// exe (references common and dll2)
public class Program
{
    public static void Main(string[] args)
    {
        var c1 = new myClass2();
        IMyClass c2 = c1.GetMyClass();
        Console.Writeline(c2.MyData);
    }
}

Answer 2

Seems no way to achieve this, if myClass is defined in dll1, since objects of type myClass may be instantiated at runtime. To avoid this, you need to change the return type of GetMyClass() in dll2 to return something defined in dll2. It can be a class quite similar to myClass and having the same properties (you can even use tools like AutoMapper to easily convert between objects), but it definitely should be in dll2. Something like:

// dll1
class myClass
{
    ...
}

myClass GetMyClass()
{
    ...
}

// dll2
class myClass2
{
    public myClass2(myClass c)
    {
        // instantiate myClass2 with values from myClass
    }
}

myClass2 GetMyClass()
{
    // somehow get myClass and convert it to myClass2 here
}