How to bind Signal to enabled property of UIButton in Reactive Cocoa 4

Question

I have a very simple use case for ReactiveCocoa. In my setup, I have two UITextFields and one UIButton.

The button's enabled property should only be set to true iff both textfields contain at least one character.

I started out creating a Signal<Bool, NoError> that emits true or false depending on the the above mentioned condition.

Now, as far as I understand I somehow need to bind the signal (or its values) to the enabled property of my button. But I have no clue how to do this and more than an hour of research haven't lead to any results...

UPDATE: From what I understand, this could previously be achieved using the RAC macro: RAC(self.button, enabled) = signal;, or something along those lines. But that doesn't help me since the macros have been deprecated in RAC 3. My question is basically the same as this one only for RAC 4 instead of 3.

score 3 · Accepted Answer · answered Dec 14 '15 at 17:41

This can be achieved using the custom <~ operator. However, it only works on properties of type MutableProperty, so we can't just do the following:

let signal: <Bool, NoError> = ...
button.enabled <~ signal

Instead, we need to wrap the button's enabled property in a MutableProperty like so:

extension UIButton {
    public var rac_enabled: MutableProperty<Bool> {
        return lazyMutableProperty(self, key: &AssociationKey.text, setter: { self.enabled = $0 }, getter: { self.enabled })
    }
}

Note that this implementation depends on this gist which was created by Colin Eberhardt.

Now we can just do:

button.rac_enabled <~ signal

How to bind Signal to enabled property of UIButton in Reactive Cocoa 4

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