How to remove observer using ReactiveCocoa?

Question

How to stop receiving new name after some event?

[RACObserve(self, username) subscribeNext:^(NSString *newName) {
    if ([newName isEqualToString:@"SomeString"])
    {
       //Do not observe any more
    }
}];

P.S. Sorry for obvious question, but I can't find answer

score 11 · Answer 1 · answered May 26 '15 at 16:04

11

You can use method 'dispose' of RACDisposable object which be returned from 'subscribeNext'.

__block RACDisposable *handler = [RACObserve(self, username) subscribeNext:^(NSString *newName) {
    if ([newName isEqualToString:@"SomeString"]) {
        //Do not observe any more
        [handler dispose]
    }
}];

answered May 26 '15 at 16:04

KM Gorbunov

111
6

Thanks! That's what I wanted to see. – serj May 27 '15 at 08:41
If `self.username` is equal to 'SomeString' before this line of code, the handler will not dispose, am I right? – KudoCC Sep 02 '17 at 07:21

score 9 · Answer 2 · answered Apr 15 '15 at 17:34

It's important to think about things a little differently in ReactiveCocoa: you don't want to "remove" an observer, you want to create a signal that completes when something happens.

You can use takeUntilBlock: to derive a signal that will stop sending values after a certain time:

[[RACObserve(self, username) takeUntilBlock:^(NSString *name) {
    return [name isEqualToString:@"something"];
}] subscribeNext:^(NSString *name) {
    NSLog(@"%@", name);
}];

But that will not send a next for the string @"something", only the names before it. If that's desired, you could append it:

NSString *sentinel = @"something";
[[[RACObserve(self, username) takeUntilBlock:^(NSString *name) {
    return [name isEqualToString:sentinel];
}] concat:[RACSignal return:sentinel]] subscribeNext:^(NSString *name) {
    NSLog(@"%@", name);
}];

It's not very elegant, but you could make a takeUntilBlockInclusive helper that would get you this behavior, and hide the grossness in there.

How to remove observer using ReactiveCocoa?

2 Answers2