How to bind Realm objects changes? - ios

Question

In my project im trying to work via MVVM,
so in VM in .h file
#property (nonatomic, strong) NSArray *cities;
in .m file
- (NSArray *)cities {
return [[GPCity allObjects] valueForKey:#"name"];
}
GPCity is a RLMObject subclass
How to bind this via ReactiveCocoa (i mean see all cities updates/adds/removes) ?
Something like:
RAC(self, cities) = [[GPCity allObjects] map:(GPCity *)city {return city.name;}];

Answer 1

You can wrap Realm change notifications in a RAC signal:
#interface RLMResults (RACSupport)
- (RACSignal *)gp_signal;
#end
#implementation RLMResults (RACSupport)
- (RACSignal *)gp_signal {
return [RACSignal createSignal:^(id<RACSubscriber> subscriber) {
id token = [self.realm addNotificationBlock:^(NSString *notification, RLMRealm *realm) {
if (notification == RLMRealmDidChangeNotification) {
[subscriber sendNext:self];
}
}];
return [RACDisposable disposableWithBlock:^{
[self.realm removeNotification:token];
}];
}];
}
#end
and then do:
RAC(self, cities) = [[[RLMObject allObjects] gp_signal]
map:^(RLMResults<GPCity *> *cities) { return [cities valueForKey:#"name"]; }];
This will unfortunately update the signal after every write transaction, and not just ones which modify cities. Once Realm 0.98 is released with support for per-RLMResults notifications, you'll be able to do the following, which will only update when a GPCity object is updated:
#interface RLMResults (RACSupport)
- (RACSignal *)gp_signal;
#end
#implementation RLMResults (RACSupport)
- (RACSignal *)gp_signal {
return [RACSignal createSignal:^(id<RACSubscriber> subscriber) {
id token = [self addNotificationBlock:^(RLMResults *results, NSError *error) {
if (error) {
[subscriber sendError:error];
}
else {
[subscriber sendNext:results];
}
}];
return [RACDisposable disposableWithBlock:^{
[token stop];
}];
}];
}
#end