How to detect if VoiceOver is on in MacOS?

Question

I am working on a MacOS app, and I cannot figure out how to listen to accessibility status changes (for example, when VoiceOver is turned on or off).

In iOS, there is a notification I can listen to, UIAccessibilityVoiceOverStatusDidChangeNotification .

Is there an equivalent in MacOS?

Answer 1

It turns out there is a hidden api to listen to the accessibility notification. You can listen to @"NSApplicationDidChangeAccessibilityEnhancedUserInterfaceNotification"

  [center addObserver:self
             selector:@selector(onAccessibilityStatusChanged:)
                 name:@"NSApplicationDidChangeAccessibilityEnhancedUserInterfaceNotification"
               object:nil];

and then in the method, you can check voiceOverEnabled which is introduced in 10.13

if(@available(macOS 10.13, *)) {
    NSWorkspace * ws = [NSWorkspace sharedWorkspace];
    NSLog(@"got notification voiceover enabled ? %d",ws.voiceOverEnabled);
  }

Answer 2

On macOS, the correct way to do this is via KVO:

[[NSWorkspace sharedWorkspace] addObserver:self forKeyPath:@"voiceOverEnabled" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:nil];

with the accompanying handler method:

- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {
 
    if ([keyPath isEqualToString:@"voiceOverEnabled"]) {
        // handle the event in your way.
        //
    } else {
        // Any unrecognized context must belong to super
        [super observeValueForKeyPath:keyPath
                             ofObject:object
                               change:change
                               context:context];
    }
}

On iOS and tvOS, use:

[[NSNotificationCenter defaultCenter] addObserverForName:UIAccessibilityVoiceOverStatusDidChangeNotification
                                                  object:nil
                                                   queue:nil
                                              usingBlock:^(NSNotification * _Nonnull note) {
      // handle the event in your way.
    }];