userDefaults: automatically register defaults from Settings.bundle

If you manage you app settings via a Setting.bundle for Settings.app, you may have experienced some strange behaviour: Even if default values for all keys are defined in your bundle, these settings aren’t automatically honoured by iDevices. If you try to load one of these settings by

id someObject = [[NSUserDefaults standardUserDefaults] objectForKey:@"myKey"];

someObject will be nil, the value stored as default in Settings.bundle is ignored.

That’s kind of normal as the method mentioned above reads from userDefaults and not from Settings.bundle – and default values from Settings.bundle aren’t automatically copied to userDefaults: In fact, some settings (booleans, for example) are at least written to userDefaults the first time Settings.app is launched after installing the app. But other settings (such as NSNumbers) aren’t even written out then – they’re only copied to userDefaults after changing them to values different from the default values in Settings.bundle. To make a long story short: Defaults in Settings.bundle give defaults values for Settings.app. But they are of no help help when reading values from userDefaults in your own app.

But wouldn’t it be useful if default settings from Settings.bundle would automatically be written to userDefaults if the user hasn’t specified any setting yet, such as to be able to count on the defaults you specify in your Settings.bundle?

I searched for a solution and stumbled upon a thread on StackOverflow. The code suggested there is a nice starting point but it counts on ALL values being well written into userDefaults if ONE value is readable. That’s not quite reliable because, as I mentioned, e.g. NSNumbers are not written unless they are different from the defaults.

So I adapted the snippet from StackOverflow to check every single value mentioned in Settings.bundle: If it’s already readable from userDefaults, nothing rests to be done. If it’s not yet readable, the value from Settings.bundle is written to userDefaults.

As a result, defaults from Settings.bundle can finally be taken for granted: When reading the value for a certain key there will always be an return value – either the user’s setting or, ifthere is none yet, the default you specify in Settings.bundle.

- (void)registerDefaultsFromSettingsBundle
{
NSLog(@"Registering default values from Settings.bundle");
NSUserDefaults * defs = [NSUserDefaults standardUserDefaults];
[defs synchronize];

NSString *settingsBundle = [[NSBundle mainBundle] pathForResource:@"Settings" ofType:@"bundle"];

if(!settingsBundle)
{
   NSLog(@"Could not find Settings.bundle");
   return;
}

NSDictionary *settings = [NSDictionary dictionaryWithContentsOfFile:[settingsBundle stringByAppendingPathComponent:@"Root.plist"]];
NSArray *preferences = [settings objectForKey:@"PreferenceSpecifiers"];
NSMutableDictionary *defaultsToRegister = [[NSMutableDictionary alloc] initWithCapacity:[preferences count]];

for (NSDictionary *prefSpecification in preferences)
{
   NSString *key = [prefSpecification objectForKey:@"Key"];
   if (key)
   {
      // check if value readable in userDefaults
      id currentObject = [defs objectForKey:key];
      if (currentObject == nil)
      {
         // not readable: set value from Settings.bundle
         id objectToSet = [prefSpecification objectForKey:@"DefaultValue"];
         [defaultsToRegister setObject:objectToSet forKey:key];
         NSLog(@"Setting object %@ for key %@", objectToSet, key);
         }
      else
         {
         // already readable: don't touch
         NSLog(@"Key %@ is readable (value: %@), nothing written to defaults.", key, currentObject);
         }
      }
   }

[defs registerDefaults:defaultsToRegister];
[defaultsToRegister release];
[defs synchronize];
}

Tell me about your mileage!