How can dark mode be detected on macOS 10.14?

Question

In macOS 10.14 users can choose to adopt a system-wide light or dark appearance and I need to adjust some colours manually depend of the current mode.

Answer 1

Since the actual appearance object you usually get via effectiveAppearance is a composite appearance, asking for its name directly probably isn't a reliable solution.

Asking for the currentAppearance usually isn't a good idea, either, as a view may be explicitly set to light mode or you want to know whether a view is light or dark outside of a drawRect: where you might get incorrect results after a mode switch.

The solution I came up with looks like this:

BOOL appearanceIsDark(NSAppearance * appearance)
{
    if (@available(macOS 10.14, *)) {
        NSAppearanceName basicAppearance = [appearance bestMatchFromAppearancesWithNames:@[
            NSAppearanceNameAqua,
            NSAppearanceNameDarkAqua
        ]];
        return [basicAppearance isEqualToString:NSAppearanceNameDarkAqua];
    } else {
        return NO;
    }
}

You would use it like appearanceIsDark(someView.effectiveAppearance) since the appearance of a specific view may be different than that of another view if you explicitly set someView.appearance.

You could also create a category on NSAppearance and add a - (BOOL)isDark method to get someView.effectiveAppearance.isDark (better chose a name that is unlikely to be used by Apple in the future, e.g. by adding a vendor prefix).

Answer 2

I have used the current appearance checking if the system is 10.14

+ (BOOL)isDarkMode {
    NSAppearance *appearance = NSAppearance.currentAppearance;
    if (@available(*, macOS 10.14)) {
        return appearance.name == NSAppearanceNameDarkAqua;
    }

    return NO;
}

And to detect the change of mode in a view the methods are:

- (void)updateLayer;
- (void)drawRect:(NSRect)dirtyRect;
- (void)layout;
- (void)updateConstraints;

And to detect the change of mode in a view controller the methods are:

- (void)updateViewConstraints;
- (void)viewWillLayout;
- (void)viewDidLayout;

Using notification:

// Monitor menu/dock theme changes...
[NSDistributedNotificationCenter.defaultCenter addObserver:self selector:@selector(themeChanged:) name:@"AppleInterfaceThemeChangedNotification" object: nil];

-(void)themeChanged:(NSNotification *) notification {
    NSLog (@"%@", notification);
}

For more information Dark Mode Documentation