ReactiveCocoa: block is never executed - objective-c

Question

In my app, I have a download manager. After any of tasks is finished I need to get all data for tableView again and reload it. But I can't get data inside RACObserve signal. Here's my code.
NSArray *activeTasks = [[DownloadManager instance] tasksToProcess];
for (DownloadTask *task in activeTasks) {
[[[self
checkTask:task]
map:^(id value
return [self fetchDownloadedData];
}]
subscribeNext:^(NSArray *models) {
// models returns RACDynamicSignal not NSArray
NSLog(#"%#", models); // <RACDynamicSignal: 0x11611cb50> name:
NSLog(#"checktask next");
} completed:^{
// This is never being executed
NSLog(#"checktask completed");
}];
}
- (RACSignal *)checkTask: (DownloadTask *)task {
return [RACObserve(task, isFinished) map:^id(id _) {
return nil;
}];
}
- (RACSignal *)fetchDownloadedData {
return [[MyCoreDataModel fetchAll] flattenMap:^id(NSArray *models) {
// This is never being executed
return [models filter:^BOOL(MyCoreDataModel *model) {
return model.isDownloaded;
}];
}];
}
- (RACSignal *)fetchAll
{
return [[[MyCoreDataModel findAll] sortBy:#"title"] fetch];
}
Would be great if someone helps me getting where is my mistake is. Thanks in advance.

Answer 1

There are few mistakes:
In map function you use method which returns RACSignal - it's not correct. You should use flattenMap instead.
Complete block will never be called, because RACObserve - hot signal, it only sends next event.
I wrote small example, I hope it helps you.
NSMutableArray<RACSignal *> *signals = [NSMutableArray array];
for (DownloadTask *task in activeTasks) {
RACSignal *signal = [[RACObserve(task, isFinished) ignore:#NO] take:1];
[signals addObject:signal];
}
#weakify(self);
[[[RACSignal merge:signals] flattenMap:^RACStream *(id _) {
#strongify(self);
return [self fetchDownloadedData];
}] subscribeNext:^(NSArray *models) {
}];
Here I created array of signals. Each signal - observing the isFinished property. Also I added ignore:#NO] take:1]; - I think it's more right, because you only need YES value and after that no observe anymore (take:1). Then I merge these signals and each time when someone of them sends finished state, we fetch data.
Please, let me know if something is not understand, I try to explain more clearly.