Objective-C equivalent to Java's anonymous classes in class methods

Question

I want to set the delegate of an object inside a class method in Objective-C. Pseudo-code:

+ (ClassWithDelegate*) myStaticMethod {
    if (myObject == nil) {
        myObject = [[ClassWithDelegate alloc] init];
        // myObject.delegate = ?
    }
    return myObject;
}

In Java I would simply create an anonymous class that implemented the delegate protocol. How can I do something similar in Objective-C?

Basically I would like to avoid creating a separate class (and files) to implement a simple delegate protocol.

Answer 1

As JeremyP has rightly said, There are no anonymous classes in Objective C like there are in Java.

But in Java, anonymous classes are mostly used to implement single method interface or what we also call as a functional interface.

We do it to avoid having to implement the interface** in a class **just for one method implementation which is most commonly used for Listeners, Observers and event handlers.

This is mostly done because of **lack of anonymous first class functions in Java (prior to version 8 and project lambda).

Objective C has something called as blocks, where you can directly pass a block which contains the implementation of that single method rather than an empty class wrapping it up.

Example:

A use of Anonymous Class in Java

//Functional interface
interface SomethingHandler 
{
  void handle(Object argument);
}

//a method that accepts the handler in some other class
class SomeOtherClass
{ 
  void doSomethingWithCompletionHandler(SomethingHandler h){
      // do the work that may consume some time in a separate thread may be.
      // when work is done call the handler with the result which could be any object
      h.handler(result);
  };
}

// Somewhere else in some other class, in some other code
// passing the handler after instantiating someObj as an object of SomeOtherClass which can use the handler as needed
SomeOtherClass someObj = new SomeOtherClass();
someObj.doSomethingWithCompletionHandler( new SomethingHandler()
                        {
                              void handle(Object argument)
                              {
                                // handle the event using the argument
                              }
                         });

In Objective C

// declare the handler block 
typedef void (^SomethingHandler)(id argument){}

// this interface is different than Java interface  which are similar to Protocols
@interface SomeOtherClass
 -(void)doSomethingWithCompletionHandler:(SomethingHandler)h;
@end

@implementation SomeOtherClass
 -(void)doSomethingWithCompletionHandler:(SomethingHandler)h
 {
          // do the work that may consume some time in a separate thread may be.
          // when work is done call the handler with the result which could be any object
          h(result);
 }

@end

  // passing the handler after instantiating someObj as an object of SomeOtherClass which can use the handler as needed

SomeOtherClass* someObj = [[SomeOtherClass alloc] init]; // ARC :)

[someObj doSomethingWithCompletionHandler:^(id argument)
                                            {
                                               // handle the event using the argument
                                            }];