Doing tweak settings the right-er way

Posted on Feb 15, 2015 by kirb — Comments

As it turned out, retrieving tweak settings from NSUserDefaults as outlined in the post I wrote a few months ago proved to not be very robust and still had problems within a sandboxed process.

At one point several months prior to the libcephei update a few weeks ago, I thought about how preferences loading could be improved, and started working on a class called HBPreferences. The idea is that either you keep an instance of this class as a global variable in your tweak, and use it basically as you would with NSUserDefaults. Or, you can take it one step further than what NSUserDefaults is capable of and “register” a variable’s pointer so it’ll always be up to date with no preference reloading code required in your tweak.

If you don’t already understand the changes made in iOS 8, refer to the first few paragraphs of the original post.

Setting up libcephei with Theos

You will need to copy libcephei’s headers and libraries to your development machine so the compiler and linker respectively are aware of it.

You won’t find libcephei in Cydia by searching for “Cephei” because it’s been set as hidden. However, you can install a package that depends on it like TypeStatus, or install “APT 0.7 Strict” (apt7) if you don’t already have it and run:

apt-get install ws.hbang.common

On your development machine, copy the required files like so:

THEOS=/opt/theos  # if you don't already have $THEOS set, set it to the location of theos
THEOS_DEVICE_IP=iphone  # and set these two if you haven't already

scp -P $THEOS_DEVICE_PORT root@$THEOS_DEVICE_IP:/usr/lib/libcephei\* $THEOS/lib
scp -r -P $THEOS_DEVICE_PORT root@$THEOS_DEVICE_IP:/usr/include/\{Cephei,CepheiPrefs\} $THEOS/include

Now, open your project’s makefile and add:

TargetName_LIBRARIES += cephei

In your control file, add ws.hbang.common to your dependencies, and set it to require the latest version or newer. At the time of writing, that’s version 1.2, so for example:

Depends: mobilesubstrate, ws.hbang.common (>= 1.2)

NSUserDefaults compatible method

This method has almost no changes from the example on the original post - just replace NSUserDefaults with HBPreferences and initialise with the initWithIdentifier: method like so:

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";

HBPreferences *preferences;

%ctor {
	preferences = [[HBPreferences alloc] initWithIdentifier:kHBCBPreferencesDomain];

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

I use constants for strings that shouldn’t ever change - you don’t need to but I’d recommend it. If you prefer, you can also set keys on preferences.defaults directly, as it’s an NSMutableDictionary.

Once again, it’s as simple as [preferences objectForKey:kHBCBPreferencesEnabledKey] to get an Objective-C object (or nil if there’s no value and no default registered), or get a primitive directly using any of bool, double, integer, or floatForKey:.

Legacy library support

As mentioned in the previous post, at the time that Cobalia was written, Flipswitch was not yet updated to support the new preferences system. Here is how it was fixed - by reading the plist from the disk and copying the data into the in-memory preferences cache:

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

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

%ctor {
	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.

Variable registration

Finally, I want to explain the most powerful feature of HBPreferences: being able to “register” a variable so that its value is always kept up to date. This is quite easy to do:

BOOL enabled;
NSArray *switches;
BOOL sectionLabel, switchLabel;

%ctor {
	HBPreferences *preferences = [HBPreferences preferencesWithIdentifier:@"ws.hbang.cobalia"];

	[preferences registerBool:&enabled default:YES forKey:@"Enabled"];
	[preferences registerObject:&switches default:@[ /* ... */ ] forKey:@"Switches"];
	[preferences registerBool:&sectionLabel default:YES forKey:@"SectionLabel"];
	[preferences registerBool:&switchLabel default:YES forKey:@"SwitchLabels"];

In your preference specifiers, ensure you have the PostNotification key set to the identifier you pass in to HBPreferences, followed by /ReloadPrefs. For example:


And that’s it - now all you need to do is refer to these variables as you always would. You don’t need to worry at all about what happens when the user changes a setting; HBPreferences takes care of it for you and updates your variables.

If you want to learn more about what libcephei can do, take a look at its documentation.