Overview

Creates a signal which observes KEYPATH on TARGET for changes.

In either case, the observation continues until TARGET or self is deallocated. If any intermediate object is deallocated instead, it will be assumed to have been set to nil.

Make sure to @strongify(self) when using this macro within a block! The macro will always reference self, which can silently introduce a retain cycle within a block. As a result, you should make sure that self is a weak reference (e.g., created by @weakify and @strongify) before the expression that uses RACObserve.

Examples

// Observes self, and doesn't stop until self is deallocated.
RACSignal *selfSignal = RACObserve(self, arrayController.items);

// Observes the array controller, and stops when self _or_ the array
// controller is deallocated.
RACSignal *arrayControllerSignal = RACObserve(self.arrayController, items);

// Observes obj.arrayController, and stops when self _or_ the array
// controller is deallocated.
RACSignal *signal2 = RACObserve(obj.arrayController, items);

@weakify(self);
RACSignal *signal3 = [anotherSignal flattenMap:^(NSArrayController *arrayController) {
    // Avoids a retain cycle because of RACObserve implicitly referencing
    // self.
    @strongify(self);
    return RACObserve(arrayController, items);
}];

Returns a signal which sends the current value of the key path on subscription, then sends the new value every time it changes, and sends completed if self or observer is deallocated.