Question

The client framework uses a callback mechanism to notify the application when messages arrive from the server. Some examples of events that are sent include login success or failure, subscription success or failure, or a change to a MBO.

Register the callback object by executing:

MyCallbackHandler* theCallbackHandler = [MyCallbackHandler new];
[SampleApp_SampleAppDB registerCallbackHandler:theCallbackhandler];

What does ths means.. pleas help out?

Answer 1

It means that the method registerCallbackHandler: accepts an object that conforms to a protocol (eg. SampleAppHandlerProtocol) that requires some methods to be implemented on your MyCallbackHandler class definition. Practical example:

@protocol CallbackHandler
-(void)reportSomethingFinished;
@end

@class SampleApp
{
  CallbackHandler *handler;
}

-(void)registerCallbackHandler:(CallbackHandler*)handler;
-(void)doSomething;
@end

In this way you must implement a class that conforms to CallbackHandler so that SampleApp can call your reportSomethingFinished from its code.