Shaw Shaw - 1 year ago 195
Swift Question

RACObserve(object, keyPath) in ReactiveCocoa 5.0

I want to monitor the UIButton.enabled property to change the button.titleColor

I have done in OC like this:

#import "ViewController.h"
#import <ReactiveCocoa/ReactiveCocoa.h>

@interface ViewController () <UITextViewDelegate>

@property (weak, nonatomic) IBOutlet UIButton *btn;


@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];

[self initUI];

- (void)initUI {

__weak typeof(self) weakSelf = self;
[[RACObserve(self.btn, enabled) map:^id(id value) {
return [value boolValue] ? [UIColor greenColor] : [UIColor redColor];
}] subscribeNext:^(id x) {
[weakSelf.btn setTitleColor:x forState:UIControlStateNormal];


- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
self.btn.enabled = !self.btn.enabled;


Now, i try to achieve the same goal in swift use the lastest Version of ReactiveCocoa, how to do?

Answer Source

ReactiveCocoa 5.0 will add UIKit Extensions.

With button.reactive.values(forKeyPath:)

This works for me in a simple Playground:

button.reactive.values(forKeyPath: "enabled")
    .map { $0 as? Bool }
    .map { enabled in enabled ? : }
    .startWithValues { [weak button = button] color in
        button?.setTitleColor(color, for: .normal)

However, this is not encouraged because

  1. UIKit does not comply to KVO and if its working, its just coincidental.
  2. Arguably, your "truth" should not be in the UI / the button, but you should have a model somewhere that determines if the button is enabled or not.

With a model

In this example a simple MutableProperty is used as model, this could be in a ViewModel or wherever

let buttonEnabled = MutableProperty<Bool>(false)

button.reactive.isEnabled <~ buttonEnabled
    .map { enabled in enabled ? : }
    .startWithValues { [weak button = button] color in
        button?.setTitleColor(color, for: .normal)

Unfortunaetly you can not bind directly to the buttons title color as you can with isEnabled

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