Question

hi i have two classes, example: ftp1 (handles normal ftp stuff), ftp2 (handles secure ftp connections, and stuff). based on a configuration setting I need to instantiate a type that can be one of these two types as a class level variable. Is this possible, if so, can someone point me in the right direction. I’ve tried to apply polymorphism to this situation, but I’m a little confused as to how to do that?

Answer 1

If the two FTP classes are part of a third-party framework (and do not already implement a common base class), you have two options:

Wrap the classes in a new class, which implements a common base class or interface

//Interface for original library classes.
public someClass {
    public void DoSomething();
}

public someClass2 {
    public void DoSomething();
}

//Wrapper implementation
public wrappedSomeClass : baseSomeClass {
    private someClass mSomeClass;

    public wrappedSomeClass() {
        mSomeClass = new someClass();
    }

    //DoSomething will need to be defined in baseSomeClass
    public overrides void DoSomething() {
        mSomeClass.DoSomething();
    }
}

public wrappedSomeClass2 : baseSomeClass {
    private someClass2 mSomeClass2;

    public wrappedSomeClass2() {
        mSomeClass2 = new someClass2();
    }

    //DoSomething will need to be defined in baseSomeClass
    public overrides void DoSomething() {
        mSomeClass2.DoSomething();
    }
}

Once the wrappers are written, you write your new code using the wrapper classes.

Store the values in a variable of type Object

The object data type is the common base for all classes. Your code would look like this:

public someclass {
    private object myVariable;
    private void somemethod() {
        if(something) {
            myVariable = new something();
        } else {
            myvariable = new something2();
        }
    }
}

When you use the value of the variable, you will almost always need to cast it back to its original type.

if(something) {
    ((something)myVariable).InvokeMethod();
} else {
    ((something2)myVariable).InvokeMethod();
}