接口继承

Question

I have an interface called IStrategy :

public interface IStrategy
{
}

I have another interface called IClickStrategy that inherits from IStrategy . It has a method called GetClicks() :

public interface IClickStrategy : IStrategy
{
   void GetClicks(string[] args);
}

And a class that inherits from IClickStrategy and implements the GetClicks() method:

public class UnionenClicksController : IClickStrategy
{
    Models.DMDelivery.Unionen model;
    Logger logger;

    public UnionenClicksController()
    {
        this.model = new Models.DMDelivery.Unionen();
        this.logger = new Logger();
    }

    public void GetClicks(string[] args)
    {
        ...
    }
}

On my main method, depending on the type of strategy I would like to decide what to do.So before everything I have:

IStrategy strategy = null;

And then if the input parameters wanted to get clicks information I would like to invoke the GetClicks function from my class UnionenClicksController() .

But as can be seen, I cannot see the GetClicks() function. However if I change my strategy to an IClickStrategy , then it will see my GetClicks. But that's not what I want because I may have a different strategy other than clicks and I don't want to declare it at the beginning of my main method.

What is it that I'm doing wrong? Thanks.

Answer 1

IStrategy doesn't contain GetClicks , it is to be found in IClickStrategy interface.

Change

IStrategy strategy = null;

to

IClickStrategy strategy = null;

You can also try casting it to proper interface,

if you are sure that it implements correct interface:

((IClickStrategy)strategy).GetClicks();

if you are unsure:

var s = strategy as IClickInterface;
if (s != null)
{
    s.GetClicks();
}

Answer 2

You have to either cast for each case, or have a virtual method in IStrategy that chooses the right method.

The latter solution is impossible if an object implement several strategies.

Answer 3

IStrategy strategy = null;

.
.
.  later on you find that you need to see if it contains a IClickStrategy ..
.

IClickStrategy clicker = strategy as IClickStrategy;

if(clicker != null) {
  clicker.GetClicks(...);
}

Answer 4

Try it

IClickStrategy strategy = null;

because UnionenClicksController does not inherit IStrategy.

Answer 5

Sure you do. But the compiler doesn't know that. You just told him, you want to treat strategy as an IStrategy . You were very explicit about that. Now...

Don't confuse the name strategy with your UnionenClicksControler object - it is just a name for the object. And the name has a type. If you want to get at the GetClicks() method, just do:

(strategy as IClickStrategy).GetClicks(args);

I have not tried this myself yet, since I haven't got around to, but doing

dynamic strategy;

might also solve your problem... but you probably forfeit any IntelliSense magic...

Answer 6

Try using this:

if(strategy is IClickStrategy)
    (strategy as IClickStrategy).GetClicks();

Technically you need to check for the type of the object first, then cast it in order to see the inheriting interface's method.

Answer 7

Thanks for all the answers but I found two solutions to my problem:

First, is to not use the line:

IStrategy strategy = null;

And postpone it until after every switch statement and then declare the strategy as a IClickStrategy.

Second, if I want to keep my IStrategy strategy = null; line I moved the GetClicks method one level up in my IStrategy interface and gave it a more general name: GetItems .

And now my switch case looks like this:

case "GETCLICKSUNIONEN":
    strategy = new UnionenClicksController();
    strategy.GetItems(args);                            
    break;