Doing tweak settings the right way

Posted on Nov 26, 2014 by kirb — Comments

Please refer to the revision of this post.

You might have noticed that tweak settings have suddenly started acting different in iOS 8. This is because the cfprefsd concept from OS X (as long ago as in 10.8 Mountain Lion) has been brought across to iOS 8. When you change a setting now, the dictionary is no longer committed to disk immediately - rather, it’s kept in memory by cfprefsd and only flushed to disk when the appropriate process (or cfprefsd itself) terminates. So with that in mind, how do you manage settings on iOS 8 now?

It’s actually really simple and I’d argue a thousand times better than the hack all of us were using before this. First, you need to keep an instance of NSUserDefaults hanging around, and register your default preferences:

static NSString *const kHBCBPreferencesDomain = @"ws.hbang.cobalia";
static NSString *const kHBCBPreferencesEnabledKey = @"Enabled";
static NSString *const kHBCBPreferencesSwitchesKey = @"Switches";
static NSString *const kHBCBPreferencesSectionLabelKey = @"SectionLabel";
static NSString *const kHBCBPreferencesSwitchLabelsKey = @"SwitchLabels";

NSUserDefaults *userDefaults;

%ctor {
	userDefaults = [[NSUserDefaults alloc] _initWithSuiteName:kHBCBPreferencesDomain container:[NSURL URLWithString:@"/var/mobile"]];

	[userDefaults registerDefaults:@{
		kHBCBPreferencesEnabledKey: @YES,
		kHBCBPreferencesSwitchesKey: @[ /* ... */ ]
		kHBCBPreferencesSectionLabelKey: @YES,
		kHBCBPreferencesSwitchLabelsKey: @YES
	}]
}

You’ll probably need to define this private init method in a category interface like so:

@interface NSUserDefaults (Private)

- (instancetype)_initWithSuiteName:(NSString *)suiteName container:(NSURL *)container;

@end

I use constants for strings that shouldn’t ever change - you don’t need to but I’d recommend it.

Now, it’s as simple as a [userDefaults boolForKey:@"Enabled"] to grab a boolean, or objectForKey: for an Objective-C object, or any of the other methods the class supports.

Easy! If you notice, you don’t even need to watch for a traditional Darwin notification, nor do you need to define PostNotification on your preferences specifiers. The important thing to note is you need to directly call the methods on NSUserDefaults where ever you need to get a preference value in your code. You shouldn’t store the preferences in separate global variables as you might have done traditionally since then you need a Darwin notification and a callback function to update them - ruining the simplicity of this solution.

But what about libraries like AppList or Flipswitch whose preferences API still write directly to the plist? The easiest thing you can do is a quick little trick to pass that back to cfprefsd to keep in memory. This is how I do it in Cobalia:

void HBCBPreferencesChanged() {
	NSDictionary *preferences = [NSDictionary dictionaryWithContentsOfFile:[[[NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES)[0] stringByAppendingPathComponent:@"Preferences"] stringByAppendingPathComponent:kHBCBPreferencesDomain] stringByAppendingPathExtension:@"plist"]];

	if (preferences[kHBCBPreferencesSwitchesKey]) {
		[userDefaults setObject:preferences[kHBCBPreferencesSwitchesKey] forKey:kHBCBPreferencesSwitchesKey];
	}
}

%ctor {
	HBCBPreferencesChanged();
	CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), NULL, (CFNotificationCallback)HBCBPreferencesChanged, CFSTR("ws.hbang.cobalia/ReloadPrefs"), NULL, kNilOptions);
}

Obviously you’ll also need to set the appropriate key in your preference specifiers for a Darwin notification to be posted with the name you provide.

If you’d like to see what else people are using for their tweaks, there are a few others you can explore that are listed on the iPhone Dev Wiki’s updating extensions for iOS 8 article. To me, this is the most simple and elegant, and almost exactly what you’d ideally be using anyway in a standard iOS or OS X application - but you’re of course allowed to use whichever looks best to you.

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