Question

My questions is next:

For example I have object A (this is data model object). Assume that object A have some property (for example request property). Also I have object B (this is my view object).

So my problem is next: when my data model will be changed (the value for request property changed) I want to know about this events in my view (object B)

How to create this interaction between object.

For example in request is written to “some_value” and after this object B immediately know about it.

Thanks for response!

Answer 1

I would use Key Value Observing. Your view controller (not the view itself) would set itself up as an observer for the data model object and when it gets observer notifications, it would update the view.

[myDataObject addObserver: myViewController 
               forKeyPath: @"request"  
                  options: NSKeyValueObservingOptionNew
                  context: nil];

// in the view controller you need

-(void) observeValueForKeyPath: (NSString*) path
                      ofObject: (id) aDataObject
                        change: (NSDictionary*) changeDictionary
                       context: (void*) context]
{
    if (aDataObject == myDataObject
        && [path isEqualToString: @"request"])
    {
        // change you are interested in
    }
    // Call suoer implementation of this method if it implements it
}

Don’t forget to remove the observer when you are done with it.

Also, be careful in a threaded environment. Observations are notified on the same thread that the change happens on. If this is not the main thread, you’ll need to use -performSelectorOnMainThread:withObject:waitUntilDone: to make any changes to the UI.