Question

G’day all,

I have been reading about protocols and delegates for passing data between controllers.

Suppose ViewControllerA creates an instance on an object:

myObject = [[anObject alloc]init];
[myObject setProperty: value];

How does ViewControllerB access myObject’s property? How does ViewControllerB become aware of objects created by ViewControllerA?

Thanks,

Answer 1

You can use NSNotificationCenter to let who ever interested to know about the new object.
Usually this is done in the model layer, for example I have a Person object.
Define a “new person created notification” in the Person .h file

extern NSString *const NewPersonCreatedNotification;  

in the .m file

NSString *const NewPersonCreatedNotification = @"NewPersonCreatedNotification";  

When a person is created (in the init method) post the notification

    [[NSNotificationCenter defaultCenter] postNotificationName:NewPersonCreatedNotification
                                                        object:self
                                                      userInfo:nil];  

Then whoever wants to know about new persons created will need to observe this notifications , for example ViewControllerA wants to know, so in it’s init method I do:

- (id)init
{
    self = [super init];
    if (self) {
       [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(handleNewPersonCreatedNotification:)
                                                     name:NewPersonCreatedNotification
                                                   object:nil];    
    }
    return self;
}  


- (void)handleNewPersonCreatedNotification:(NSNotification *)not
{
    // get the new Person object  
    Person *newPerson = [not object];  

    // do something with it...
}