Dev:PreferenceBundles

Preference Bundles are bundles for extending the Settings application. Developers can build their own bundles and place them in /Library/PreferenceBundles/ for others to use.

Structure of a Preference Bundle
Preference bundles must have the extension .bundle. The principle class of the bundle should be a subclass of PSListController or PSViewController. When providing localization files, if a specifier plist is called spec.plist, there should be a corresponding localization file called spec.strings. The bundle can have a 29&times;29 icon, with a preferred name of icon.png.

For more information on specifiers, see Preferences Specifier Plist Format.

Issues with OS 3.2 and 4.0
PSViewController underwent a massive change after 3.1, breaking all custom subclasses on the iPad and on 4.0 - it is now a UIViewController.

Improper implementations of PSListController subclasses will fail to work properly on 4.0 and later. You must set _specifiers within the  method and return it. This is because PSListController relies on _specifiers</tt> to generate specifier metadata and group indices since iOS 4.0. Example:

Using a Preference Bundle
When creating these bundles you might use other interface elements than PSCells. When doing so you can have some that modify the preferences so you'll want to make those changes be saved. For this objective there are various APIs; aside from the, there's the CFPreferences family of functions. The following snippet shows how to save a dictionary to a "domain":

The old simple way
It is very common to load preferences in the constructor of your tweak.

It is very important to only load the preferences in the constructor and not access or modify any UI elements. If you need to do this, you can load your preferences in SpringBoard's init method.

More information about preferences can be seen here.

Into sandboxed/unsandboxed processes in iOS 8
This is a method that Karen (angelXwind) uses for several of her tweaks, notably mikoto and PreferenceOrganizer 2 as of this writing.

Her method involves overriding setPreferenceValue:specifier and readPreferenceValue: in the preference bundle to restore the old, pre-iOS 8 behaviour as it completely bypasses CFPreferences and writes directly to file.

This way, you can continue to read from the plist without worrying about cfprefsd. CFNotifications are still posted upon preference set.

This method has been tested to work in iOS 5, 6, 7, and 8.

Add this in your PSListController implementation code:

Now you can load preferences in your tweak like this:

Into unsandboxed processes (using CFPreferences)
With the release of iOS 8, it became evident that the popular plist loading method wasn't the best way to load preferences. saurik summarized it well: "As far as I can tell, the idea is that the plist file on disk is simply backing a shared memory region managed by cfprefsd, which Apple has brought to iOS from OS X 10.8. It only gets flushed when cfprefsd "feels like it". But if you ask cfprefsd for the value using the actual APIs you are supposed to use to access these files, it should work."

These "actual APIs" are documented here: https://developer.apple.com/library/mac/documentation/CoreFoundation/Reference/CFPreferencesUtils/. Perhaps you'll end up with something like this:

This was tested back to iOS 6, and it seemed to work without problems. This solution does not work if you are in third party apps or other apps that have sandboxed preferences.

The following is an alternative discovered by merdok, which lets you interact with it via dictionary API. It has the same limitations.

CFPreferencesCopyMultiple returns a CFDictionaryRef which is "toll-free bridged" with its Cocoa Foundation counterpart, NSDictionary. CFArrayRef keyList = CFAutorelease(CFPreferencesCopyKeyList(appID, kCFPreferencesCurrentUser, kCFPreferencesAnyHost)); - throws an error (maybe because it's undocumented).

(This works with the old dict objectForKey - instead  you can use the above code. This solution doesn't require any massive code modifications to support iOS8)