Touchstone

Easy defaults for use in debugging and production.

Touchstone makes it easy to create defaults that are persistent in debug builds, while being volatile in non-debug builds.

In non-debug builds, defaults specified as volatile (registered with the volatileDefaults parameter of registerDefaults:volatileDefaults:isVolatile:), are not persisted but can be written and read from. The next time defaults are registered (ex. app startup), those defaults are set to the value passed in.

However, if you pass NO to isVolatile (for example, in debug builds), then the defaults specified with the volatileDefaults parameter are not actually volatile; they are persisted and act like normal defaults.

Problem

Touchstone was created to solve a problem we at Educreations ran into frequently. We have debug settings that we want to configure in-app, and to persist between app sessions. However, we do not want those settings to be non-default in production builds.

For example, say we have a setting to change our API endpoint. In production builds, this should always be our production API endpoint. But in debug builds, we might want to default to our production endpoint, but be able to change, and persist that change, to a different endpoint.

We previously had lots of code like the following:

#if DEBUG
    if ([standardDefaults boolForKey:kLoggingEnabledKey]) {
        logger.level = AFHTTPLoggerLevelVerbose;
    } else {
        logger.level = AFHTTPLoggerLevelError;
    }
#else
    logger.level = AFHTTPLoggerLevelOff;
#endif

Touchstone was built to solve this problem of conditional debug blocks.

Examples

isVolatile:YES

Here is an example where Touchstone is configured with isVolatile: set to YES:

NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
[standardDefaults registerDefaults:@{kFirstLaunchKey: @(YES)}
                  volatileDefaults:@{kLoggingEnabledKey: @(NO)}
                        isVolatile:YES];

NSLog(@"-> %@", ([standardDefaults boolForKey:kFirstLaunchKey] ? @"YES" : @"NO"));
// -> YES
NSLog(@"-> %@", ([standardDefaults boolForKey:kLoggingEnabledKey] ? @"YES" : @"NO"));
// -> NO

// Set new values
[standardDefaults setBool:NO forKey:kFirstLaunchKey];
[standardDefaults setBool:YES forKey:kLoggingEnabledKey];

NSLog(@"-> %@", ([standardDefaults boolForKey:kFirstLaunchKey] ? @"YES" : @"NO"));
// -> NO
NSLog(@"-> %@", ([standardDefaults boolForKey:kLoggingEnabledKey] ? @"YES" : @"NO"));
// -> YES

Now restart the app...

NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
[standardDefaults registerDefaults:@{kFirstLaunchKey: @(YES)}
                  volatileDefaults:@{kLoggingEnabledKey: @(NO)}
                        isVolatile:YES];

NSLog(@"-> %@", ([standardDefaults boolForKey:kFirstLaunchKey] ? @"YES" : @"NO"));
// -> NO
NSLog(@"-> %@", ([standardDefaults boolForKey:kLoggingEnabledKey] ? @"YES" : @"NO"));
// -> NO

The key kFirstLaunchKey had the value that was set persisted, while the key kLoggingEnabledKey did not have it's value persisted and reverted to the default that was passed in to registerDefaults:volatileDefaults:isVolatile:.

isVolatile:NO

Here's an example where isVolatile: is set to NO:

NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
[standardDefaults registerDefaults:@{kFirstLaunchKey: @(YES)}
                  volatileDefaults:@{kLoggingEnabledKey: @(NO)}
                        isVolatile:NO];

NSLog(@"-> %@", ([standardDefaults boolForKey:kFirstLaunchKey] ? @"YES" : @"NO"));
// -> YES
NSLog(@"-> %@", ([standardDefaults boolForKey:kLoggingEnabledKey] ? @"YES" : @"NO"));
// -> NO

// Set new values
[standardDefaults setBool:NO forKey:kFirstLaunchKey];
[standardDefaults setBool:YES forKey:kLoggingEnabledKey];

NSLog(@"-> %@", ([standardDefaults boolForKey:kFirstLaunchKey] ? @"YES" : @"NO"));
// -> NO
NSLog(@"-> %@", ([standardDefaults boolForKey:kLoggingEnabledKey] ? @"YES" : @"NO"));
// -> YES

Now restart the app...

NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
[standardDefaults registerDefaults:@{kFirstLaunchKey: @(YES)}
                  volatileDefaults:@{kLoggingEnabledKey: @(NO)}
                        isVolatile:NO];

NSLog(@"-> %@", ([standardDefaults boolForKey:kFirstLaunchKey] ? @"YES" : @"NO"));
// -> NO
NSLog(@"-> %@", ([standardDefaults boolForKey:kLoggingEnabledKey] ? @"YES" : @"NO"));
// -> YES

Note that the only thing that changed was we passed NO to registerDefaults:volatileDefaults:isVolatile: and that the last call to get the key kLoggingEnabledKey returned YES, which is the value we had set before the app restart; it was persisted.

Check out the example project included and play around with setting the value of isVolatile: to see how it reacts.

Installation

Use CocoaPods to install or use a git submodule. Then include the necessary categories.

Contact

Chris Streeter @chrisstreeter

License

Touchstone is available under the MIT license. See the LICENSE file for more info.