How to subscribe to completion of RACCommand - ios

Question

RACSignal *s1 = [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber> _Nonnull subscriber) {
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSLog(#"s1");
[subscriber sendCompleted];
});
return nil;
}];
RACSignal *s2 = [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber> _Nonnull subscriber) {
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSLog(#"s2");
[subscriber sendCompleted];
});
return nil;
}];
self.command = [[RACCommand alloc] initWithSignalBlock:^RACSignal * _Nonnull(id _Nullable input) {
return [s1 then:^RACSignal * _Nonnull{
return s2;
}];
}];
[self.command execute:nil];
[self.command.executionSignals subscribeCompleted:^{
NSLog(#"completed");
}];
I found that completed did not excute. How to make it work?

Answer 1

RACCommand.executionSignals is one signal that belongs to the RACCommand instance.
On this signal, the command will send another RACSignal as value for each execution of the command.
With your snippet
[self.command.executionSignals subscribeCompleted:^{
NSLog(#"Command was deallocated");
}];
you are observing the RACSignal<RACSignal> of the command - this signal will only complete, when the RACSignal is deallocated.
If you really need to observe the command, you will need to do the following:
[self.command.executionSignals subscribeNext:^(RACSignal *innerSignal) {
[innerSignal subscribeCompleted:^{
NSLog(#"One execution of the command completed");
}];
}];
This subscribeNext will be called with each execute of the RACCommand and the innerSignal is the signal you want to observe.
However, if you actually want to know when a single execution is completed, you can subscribe directly to the signal thats returned from the execute call:
[[self.command execute:nil] subscribeCompleted:^{
NSLog(#"This execution of the command completed");
}];