Simulate interface in java with objective-c

I came from a java background, and I was trying to use protocol like a java interface.

In java you can have an object implement an interface and pass it to a method like this:

public interface MyInterface {
 void myMethod();
}

public class MyObject implements MyInterface {
 void myMethod() {// operations}
}



public class MyFactory {
  static void doSomething(MyInterface obj) {
     obj.myMethod();
  }
}

public void main(String[] args) {
 // get instance of MyInterface from a given factory
 MyInterface obj = new MyObject();
 // call method
 MyFactory.doSomething(obj);
}

I was wondering if it's possible to do the same with objective-c, maybe with other syntax.

The way I found is to declare a protocol

@protocol MyProtocol
-(NSUInteger)someMethod;
@end

then my object would "adopt" that protocol and in a specific method I could write:

-(int) add:(NSObject*)object {
 if ([object conformsToProtocol:@protocol(MyProtocol)]) {
   // I get a warning
   [object someMethod];
 } else {
   // other staff
 }
}

The first question would be how to remove the warning, but then in any case other caller coul开发者_开发问答d still pass wrong object to the class, since the check is done inside method. Can you point out some other possible way for this ?

thanks Leonardo

You can make the compiler do the (static) checking for you. Change you method signature to:

-(int) add:(id<MyProtocol>)object

That tells the compiler, that object can be of any class that conforms to MyProtocol. It will now warn you, if you try to call add: with an object of a class that does not conform.

Edit:

To make usage of objects that conform to MyProtocol easier, it's helpful let MyProtocol extend NSObject:

@protocol MyProtocol <NSObject>
...
@end

Now you can send messages like retain, release or respondsToSelector: to objects with a static type of id <MyProtocol>

Especially the last is helpful in cases where you use the @optional keyword in the protocol.