I am using the MVVM paradigm in my iOS with RACSignal as well. So far things have worked out great. However I am experiencing a problem when subscribing to signals. On the first subscription things work fine. However further subscriptions don't.
The code
In my viewModel I have an RACSignal declared like this:
viewModel.h
@property (strong, readonly, nonatomic) RACSignal *updatedContentSignal;
viewModel.m
@property (nonatomic, readwrite, strong) RACSubject *updatedContentSignal;
It is then initialised like so in the viewModel's designated initialiser:
self.updatedContentSignal = [[RACSubject alloc]init];
Then when I actually use the signal in the viewModel I do this sort of thing:
Where needed in various places in the viewModel - typically within a web service block method
[(RACSubject *)self.updatedContentSignal sendNext:nil];
[(RACSubject *)self.updatedContentSignal sendCompleted];
[(RACSubject *)self.updatedContentSignal sendError:error];
In the viewController I subscribe to signal like so:
[self.viewModel.updatedContentSignal subscribeNext:^(id x) {
} error:^(NSError *error) {
} completed:^{
}];
I subscribe once to the signal on viewDidLoad
So all works on the first viewDidLoad call
The problem
When I navigate away from the viewController and come back to it viewWillAppear is called, and the viewModelfires off various methods that trigger the signal:
[(RACSubject *)self.updatedContentSignal sendNext:nil];
[(RACSubject *)self.updatedContentSignal sendCompleted];
[(RACSubject *)self.updatedContentSignal sendError:error];
However the viewController no longer receives the signal. It seems it only works not he first subscription.
Is there a way to have it that the signal will continue to work each time one of the updateContent signal is call/ fired?
As your code is not very comprehensive I can only say a signal will be dismissed as soon as it is completed (either via sendCompleted: or sendError:).
So if you want to continue you'll have to only use sendNext:.
Only use sendCompleted, in case you want to show, that this is no longer used.
SendError: is used, in case you receive an error. so in your web service block you'd need something like:
if(!error) {
sendNext:xxx;
} else {
sendError:error;
}