C# – Abstract property with public getter, define private setter in concrete class possible

abstract classcgetterpropertiessetter

I'm trying to create an abstract class that defines a property with a getter. I want to leave it up to derived classes to decide if they want to implement a setter for the property or not. Is this possible?

What I have so far:

public abstract class AbstractClass {
    public abstract string Value { get; }
    public void DoSomething() {
        Console.WriteLine(Value);
    }
}

public class ConcreteClass1 : AbstractClass {
    public override string Value { get; set; }
}

public class ConcreteClass2 : AbstractClass {
    private string _value;
    public override string Value {
        get { return _value; }
    }
    public string Value {
        set { _value = value; }
    }
}

public class ConcreteClass3 : AbstractClass {
    private string _value;
    public override string Value {
        get { return _value; }
    }
    public void set_Value(string value) {
        _value = value;
    }
}

In ConcreteClass1, I get an error on the set. It can't override set_Value because no overridable set accessor exists in AbstractClass.

In ConcreteClass2, I get an error on both Value's because a member with the same name is already declared.

ConcreteClass3 doesn't give an error, but even though Value's set accessor would be compiled into set_Value, it doesn't work the other way around. Defining a set_Value does not mean that Value gets a set accessor. So I can't assign a value to a ConcreteClass3.Value property. I can use ConcreteClass3.set_Value("value"), but that's not what I'm trying to achieve here.

Is it possible to have the abstract class demand a public getter, while allowing an optional setter to be defined in a derived class?

In case you'r wondering, this is just a theoretical question. I don't have a real situation where something like this is needed. But I can imagine an abstract class that doesn't care how a property gets set, but that does need to be able to get the property.

Best Answer

Unfortunately, you can't do exactly what you want. You can do this with interfaces though:

public interface IInterface {
    string MyProperty { get; }
}

public class Class : IInterface {
    public string MyProperty { get; set; }
}

The way I would do it is to have a separate SetProperty method in the concrete classes:

public abstract class AbstractClass {
    public abstract string Value { get; }
}

public class ConcreteClass : AbstractClass {

    private string m_Value;
    public override string Value {
        get { return m_Value; }
    }

    public void SetValue(string value) {
        m_Value = value;
    }
}
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