iOS and Objective-C: How to keep an object globally - objective-c

Question

Developing an app for iOS, I need to know how to have instanced and available an object created when user authenticates.
I am using OAuth2 method properly implementing gtm-oauth2 framework. The user entries, sees the login form displayed in a web view and correctly authenticates. In that moment, as detailed in the documentation, I go like this:
if (error != nil){
// Do whatever to control the error
}
else
{
// Authentication succeeded
// Assign the access token to the instance property for later use
self.accessToken = myAuth.accessToken;
[myAuth setShouldAuthorizeAllRequests:YES];
[self setAuth:myAuth];
// Display the access token to the user
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Authorization Succeeded"
message:[NSString stringWithFormat:#"Access Token: %#", myAuth.accessToken]
delegate:self
cancelButtonTitle:#"Dismiss"
otherButtonTitles:nil];
[alertView show];
}
Later, in the same controller, I use the self.auth object like this to access my API once the user has authenticated:
[request setURL:getCartsURL];
[request setValue:self.accessToken forHTTPHeaderField:#"Authorization"];
[self.auth authorizeRequest:request
completionHandler:^(NSError *error) {
NSString *output = nil;
if (error) {
output = [error description];
} else {
// Synchronous fetches like this are a really bad idea in Cocoa applications
//
// For a very easy async alternative, we could use GTMHTTPFetcher
NSURLResponse *response = nil;
NSData *data = [NSURLConnection sendSynchronousRequest:request
returningResponse:&response
error:&error];
if (data) {
// API fetch succeeded
output = [[NSString alloc] initWithData:data
encoding:NSUTF8StringEncoding];
SBJsonParser *jsonParser = [SBJsonParser new];
// Parse the JSON into an Object
id parsed = [jsonParser objectWithString:output];
NSArray *arrayResponse = [[NSArray alloc] initWithArray:parsed];
} else {
// fetch failed
output = [error description];
}
}
}];
So far, I have been using a local instance of self.auth object, what happens to be insufficient if I want to have that object globally accessed from any point of the whole app. Ok for the init view controller, but not for the whole app.
I think I can somehow access this first view controller to get the object anytime I want it. But I guess we have better methods to have it globally instanced and accessible from any point of the app.
Can you please help me with this?
Thanks a lot.

Answer 1

You should use a Singleton. Here is a nice article on how to set one up.

Answer 2

You could change the [self setAuth:myAuth]; of that ViewController to set an object on the AppDelegate. Create it there and set it, then you'll be able to access it from anywhere.
[[UIApplication sharedApplication] delegate] will give you a pointer to your app delegate, the one that was automatically created when you made the project.