Basic Setup of iCloud and Key-Value Storage - Beginning iOS Cloud and Database Development - page 53

- (void)storeDidChange:(NSNotification *)notification {
// Get the list of keys that did change
NSDictionary *userInfo = [notification userInfo];
NSNumber *reasongForChange = [userInfo objectForKey:NSUbiquitousKeyValueStoreChangeReasonKey];
NSInteger reason = -1;
If a reason could not be determined, we shouldn't update anything.
if(!reasongForChange)
return;
Now you will update only for changes from the server.
reason = [reasongForChange integerValue];
if(reason == NSUbiquitousKeyValueStoreServerChange || reason ==
NSUbiquitousKeyValueStoreInitialSyncChange){
NSArray *changedKeys = [userInfo objectForKey:NSUbiquitousKeyValueStoreChangedKeysKey];
NSUbiquitousKeyValueStore *kvStore = [NSUbiquitousKeyValueStore defaultStore];
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[changedKeys enumerateObjectsUsingBlock:^(NSString *key, NSUInteger idx, BOOL *stop) {
id value = [kvStore objectForKey:key];
[userDefaults setObject:value forKey:key];
}];
}
}
This is a lot at first glance, but it will quickly make sense. This method receives an
NSNotification object. This is the object that is sent to us whenever the message
NSUbiquitousKeyValueStoreDidChangeExternallyNotification is received by the app. We start
off by calling the userInfo method to get the data or payload of the notification. It comes in the
form of an NSDictionary . We then extract the reason for change by getting the value for the key
NSUbiquitousKeyValueStoreChangeReasonKey . The reason is in the form of an NSNumber which we
assign to the variable reasonForChange . Then we set up an NSInteger variable “reason” and assign
it a value of -1. Setting this to -1 ensures that it doesn't conflict with any of the enum values that we
will check for. We then do a check to make sure that our reasonForChange is not nil . If it is, we return
out of this method. If not, we continue on and pull out the integerValue and assign it to reason.
Note Apple provides two constants to us for working with the userInfo dictionary of the
NSUbiquitousKeyValueStoreDidChangeExternallyNotification notification. They are
NSUbiquitousKeyValueStoreChangeReasonKey and NSUbiquitousKeyValueStoreChangedKeysKey .