Where and how should I instantiate an object which will be used globally in an IOS app?

Question

For simplicity\'s sake, lets say I am making a stopwatch application for ios5. I have a class called stopwatch, which represents the stopwatch\'s state. This class possesses

Answer 1

If you "declare it to be a member of the AppDelegate class" then you should use it as a property:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:     (NSDictionary *)launchOptions {
    Stopwatch *aStopwatch = [[Stopwatch alloc] init];
    self.stopwatch = aStopwatch;
    [aStopwatch release];
    ...
}

Later, anywhere in your code:

appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
[appDelegate doSomethingWithStopwatchMethod];
someVariable = appDelegate.stopwatch.timeSinceStart;
...

Another approach would be to use a singleton (check SO for dozens of questions on the subject) or even a plain global variable (an integer holding a flag for instance) declared in main.m.