CODEWITHSUNDEEP
c#.netoopdesign-patternsdependency-injection
loki
loki

Reputation: 2966

how to use constructor injection with abstract class?

I have been trying to learn dependency injection but I have 2 errors when I run my code:

  1. DependencyInjection.Message.Sms() must declare a body because it is not marked abstract, extern, or partial.
  2. Cannot implicitly convert type DependencyInjection.IInterface to DependencyInjection.MyClass. An explicit conversion exists (are you missing a cast?)

Is the code below a good design for DI? 

namespace DependencyInjection
{
    public interface IInterface
    {

    }

    public abstract class Message
    {
        public virtual void Sms();
    }

    public class MyClass : Message, IInterface
    {
        public override void Sms()
        {
            Console.WriteLine("Sms gönder.");
        }
    }

    public class ClassManager
    {
        private IInterface _myinterface;


        public MyClass Xyz
        {
            get { return _myinterface; }
            set { _myinterface = value; }
        }

        public ClassManager(IInterface myinterface)
        {
            _myinterface = myinterface;
        }
    }
}

Upvotes: 1

Views: 2224

Answers (3)

Azodious
Azodious

Reputation: 13872

1) DependencyInjection.Message.Sms()' must declare a body because it is not marked abstract, extern, or partial

Add abstract keyword (and remove virtual) to method declaration:

public abstract void Sms();

2) Cannot implicitly convert type 'DependencyInjection.IInterface' to 'DependencyInjection.MyClass'. An explicit conversion exists (are you missing a cast?)

private IInterface _myinterface;
public MyClass Xyz
{
    get { return _myinterface; }
    set { _myinterface = value; }
}

Xyz has return-type of type MyClass but in get you are returning _myinterface which is of type IInterface.

Change to following:

public IInterface Xyz
{
    get { return _myinterface; }
    set { _myinterface = value; }
}

Upvotes: 4

Adi Lester
Adi Lester

Reputation: 25201

  1. You're declaring a virtual method with no body. Virtual methods must declare a body that will act as the default implementation of the method. You can either declare your method as abstract, which means that the derived classes have to provide their own implementation:

    public abstract void Sms();

    or you can keep the method virtual and provide a default implementation in the base class:

    public virtual void Sms()
{
    // Default or no implementation goes here.
}

  2. In the following code you're trying to cast IInterface to MyClass, which is probably not what you want.

    public MyClass Xyz
{
    get { return _myinterface; }
    set { _myinterface = value; }
}

    you're probably looking to return IInterface instead:

    public IInterface Xyz
{
    get { return _myinterface; }
    set { _myinterface = value; }
}

Upvotes: 0

Mihai
Mihai

Reputation: 2760

Change this 

public abstract class Message
{
    public virtual void Sms();
}

to this 

public abstract class Message
{
    public abstract void Sms();
}

You either give the virtual method a body, like so

public virtual void Sms() { }

or you mark it as abstract

public abstract void Sms();

EDIT:

Forgot about the second error. Change this

public MyClass Xyz
    {
        get { return _myinterface; }
        set { _myinterface = value; }
    }

to this

public IInterface Xyz
    {
        get { return _myinterface; }
        set { _myinterface = value; }
    }

Upvotes: 0

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