NSObject does not give data UIViewController - ios

Question

Description of the problem is shown below:
Function contained in the UIViewController link functions contained in the NSObject
NSObject return value to another function contained in UIViewController
When a function referenced to UIViewController it does not update UILabel
UILabel found in UIViewController
NSObject class:
-(void)getCategoryId:(NSString *)categoryid {
categoryMap *catMap = [[categoryMap alloc] init];
[catMap getCategoryId:categoryid];
catMap.nePOI = categoryid;
}
UIViewController:
-(void)getCategoryId:(NSString *)categoryid {
self.label.text = categoryid;
}

Answer 1

You are creating an new categoryMap View controler object and you are updating its label, not the one from the categoryMap view controller that is being currently displayed.
To achieve what you want, the "NSObject" instance would have to have a refen-rence (property) pointing to the ViewController that is actually displayed on screen.
-(void)getCategoryId:(NSString *)categoryid {
// View controller is created
categoryMap *catMap = [[categoryMap alloc] init];
// label updated
[catMap getCategoryId:categoryid];
catMap.nePOI = categoryid;
// End of the method, View controller is destroyed
// See the problem here??? You are not updated the good viewController...
}
Although this is not a recommended way to go. Your viewController should ask the object what to display, not the other way around. But, in your case, you can fix this with a notification. Replace the implementation of getCategoryId: in the object class by
[[NSNotificationCenter defaultCenter] postNotificationWithName:#"categorySelected" object:categoryId];
and subscribe to it in your view controler viewDidLoad
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(getCategoryId:) name:#"categorySelected" object:nil];
and then replace the getCategoryId: method of your view controller by:
-(void)getCategoryId:(NSNotification *)notif {
self.label.text = (NSString *)(notif.object);
}
That should do... ;)
To better understand architecture behind the ViewController principles, please refer to Apple MVC documentation: https://developer.apple.com/library/mac/documentation/General/Conceptual/DevPedia-CocoaCore/MVC.html