where to addObserver in iOS

Question

I use Objective-C to develop an iOS tabBar app. When users open the app, it is in tab1. When users click a picture in tab1, the app will jump to tab3 with the picture's name.

The problem is where to call addObserver in tab3 since tab3 never opens?

It is unclear what method you mean by `addObserver` (there are at least two distinct groups of methods with that name) or why you want to do so. In general, if a view controller needs observe something when it is not on screen, you're probably violating MVC. https://developer.apple.com/library/mac/documentation/General/Conceptual/CocoaEncyclopedia/Model-View-Controller/Model-View-Controller.html If you just need to observe when you're onscreen, use `viewDidAppear` and `viewWillDisappear`. — Rob Napier, Jul 07 '16 at 00:13

score 0 · Accepted Answer · answered Jul 07 '16 at 03:41

If I get your question correctly you just want to open tab3 when you click a photo from tab 1

IMO, it should have something like window->mainController->tabController [tabs]

In your tab1Controller you can setup a delegate lets call it "Tab1ControllerDelegate" having a method named "tab1DidSelectSomething:(NSString *)something". then in your mainController you can assign the delegate to self.

 i.e.
  tab1Controller.delegate = self;

In your tab1Controller picker action you can do something like:

if(_delegate){ [_delegate tab1DidSelectSomething:<whatEverheSelected>]; }

Then in your mainController:

-(void)tab1DidSelectSomething:(NSString *)something{ // get the viewController here UIViewController *controller = _tabController.viewControllers[2]; [controller updateselected:something]; _tabController.selectedIndex = 2; }

where to addObserver in iOS

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