Adding an observer to each view or present view dynamically

Question

I am posting a notification locally in the app when ever I receive a remote notification.

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo
{
    NSLog(@"Received notification: %@", userInfo);
    [[NSNotificationCenter defaultCenter] postNotificationName:@"NEWMESSAGE" object:nil userInfo:userInfo]; }

I have added an observer to the view in the function viewWillAppear() and remove the observer in viewWillDisappear().

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(newMessageReceived:) name:@"NEWMESSAGE" object:nil];

and
[[NSNotificationCenter defaultCenter] removeObserver:self];

My question is I want to override every viewWillAppear and viewWillDisappear functions in all *.m files that use these functions in my app.

or how can I dynamically add an observer (like above) to the present view and remove the observer when that view disappears. it should be like a global action whenever view changes observer to be added and removed when it changes again.

Is this possible? if so please guide me.

thanks in advance.

Answer 1

Some thoughts:

• You can subclass UIViewController and implement these method in the subclass-ed view controller class. Then you need to create all your views as the subclass of this UIViewController.

Example:

//Creating a custom subclass of UIViewController
@interface CustomViewController : UIViewController
@end

@implementation CustomViewController

 - (void)viewWillAppear:(BOOL)animated
{
   [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(newMessageReceived:) name:@"NEWMESSAGE" object:nil];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

@end

And create all your view controller as the subclass of CustomViewController.