Ground Control additions, see description.md file below

appDelegate.m

// feature keys
#define kFeatureA @"FeatureA"

// Ground Control keys
#define GROUND_CONTROL_URL @"http://yourserver.com/gc.php?version=%@&bundle=%@&lang=%@"
#define kGroundControlLastCheck @"GroundControlLastCheck"
#define kGroundControlCheckInterval @"GroundControlCheckInterval"

@implementation LocationsAppDelegate {
  BOOL _isFeatureAEnabled;  // Example feature

  NSDate *_groundControlLastCheck;
  NSUInteger _groundControlCheckInterval;
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  ...
  // default check interval in days
  _groundControlCheckInterval = 7;
  [self initializeGroundControl];
  ...
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
  ...
  [self initializeGroundControl];
  ...
}


#pragma mark - Ground Control

- (BOOL)shouldUpdateGroundControlData {
  BOOL checkForUpdate = NO;
  
  if ([[NSUserDefaults standardUserDefaults] objectForKey:kGroundControlLastCheck]) {
    _groundControlLastCheck = [[NSUserDefaults standardUserDefaults] objectForKey:kGroundControlLastCheck];
  }
  
  if (!_groundControlLastCheck) {
    _groundControlLastCheck = [NSDate distantPast];
  }
  
  NSString *testValue = nil;
  testValue = [[NSUserDefaults standardUserDefaults] stringForKey:kGroundControlCheckInterval];
  if (testValue != nil) {
    _groundControlCheckInterval = [[NSUserDefaults standardUserDefaults] integerForKey:kGroundControlCheckInterval];
  }
  
  NSTimeInterval dateDiff = fabs([_groundControlLastCheck timeIntervalSinceNow]);
  if (dateDiff != 0)
    dateDiff = dateDiff / (60*60*24);
  
  checkForUpdate = (dateDiff >= _groundControlCheckInterval);
  
#if defined (CONFIGURATION_Debug)
  // we always tun this check on startup, because we want to test, right?
  checkForUpdate = YES;
#endif
  
  return checkForUpdate;
}

- (void)updateGroundControlFeatures {
  // update the remotely configurable features

  NSString *testValue = nil;
  
  // example feature
  testValue = [[NSUserDefaults standardUserDefaults] stringForKey:kFeatureA];
  if (testValue != nil) {
    _isFeatureAEnabled = [[NSUserDefaults standardUserDefaults] boolForKey:kFeatureA];
    // now you would somehow react on the change of this value or use the other approaches described in Ground Control docs
  }
  
  // ground control check interval in days, app default is set to 7
  testValue = [[NSUserDefaults standardUserDefaults] stringForKey:kGroundControlCheckInterval];
  if (testValue != nil) {
    _groundControlCheckInterval = [[NSUserDefaults standardUserDefaults] integerForKey:kGroundControlCheckInterval];
  }
}

- (void)initializeGroundControl {
  [self updateGroundControlFeatures];
  
  if (![self shouldUpdateGroundControlData]) return;
  
  NSString *version = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"];
  NSString *bundle = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleIdentifier"];
  NSString *language = [[[NSBundle mainBundle] preferredLocalizations] objectAtIndex:0];
  NSString *urlString = [NSString stringWithFormat:GROUND_CONTROL_URL, version, bundle, language];
  NSURL *url = [NSURL URLWithString:urlString];
  [[NSUserDefaults standardUserDefaults] registerDefaultsWithURL:url
                                                         success:^(NSDictionary *defaults) {
                                                           _groundControlLastCheck = [NSDate date];
                                                           [[NSUserDefaults standardUserDefaults] setObject:_groundControlLastCheck forKey:kGroundControlLastCheck];
                                                           
                                                           [self updateGroundControlFeatures];
                                                         }
                                                         failure:^(NSError *error) {
                                                         }];
}

Description.md

Ground Control by @mattt is a great iOS library to remotely configure your iOS app by sending plists from a server to your app and then updating the user defaults values.

I wanted to extend this a bit with the following ideas in mind:

• Define the values in a JSON file, instead of uploading an updated plist file to the server
• Define values independently for given bundle identifiers, bundle version and language combination, so I can modify e.g. beta and debug versions independently from released apps
• Values can be defined in a default language for a bundle version and overwritte on language specific entries like en. You can also only use default or only use specific languages
• Return an empty plist for all unknown bundle identifiers or bundle versions
• Don't check for config updates on every startup or every time the app becomes active, but only once a day or a remotely configurable amount of days
• Right now the server side php script only supports boolean, integer and strings since I didn't need more. Specific data types like NSDate would be more complicated, but could be used e.g. by naming conventions for the key or using objects which include a datatype key, or anything else :)

gc.json

{
  "de.buzzworks.worldviewlive" : {
    "294" : {
      "default" : {
        "FeatureA" : false,
        "GroundControlCheckInterval" : 7
      },
      "en" : {
        "FeatureA" : true
      }
    }
  },
  "de.buzzworks.worldviewlivebeta" : {
    "294" : {
      "default" : {
        "FeatureA" : false,
        "GroundControlCheckInterval" : 7
      }
    }
  },
  "de.buzzworks.worldviewlivedebug" : {
    "294" : {
      "default" : {
        "FeatureA" : false,
        "GroundControlCheckInterval" : 7
      }
    }
  }
}

gc.php

<?php
  
  //
  // plist writer library from http://www.j-schell.de/node/456
  // code for the plist write is here: http://www.j-schell.de/files/n456_plist_writer.html
  //
  
  include ( 'plistwriter.inc' );
  
  header('content-type: application/x-plist');
  
  function finish() {
    $arr = array ($key=>$value);
    $x = new record_item ( ); // start plist with record
  
    die($x); // display the property list.
  }
  
  $allowed_args = ',version,bundle,lang,';
  
  foreach(array_keys($_GET) as $k) {
    $temp = ",$k,";
    if(strpos($allowed_args,$temp) !== false) { $$k = $_GET[$k]; }
  }
  
  if (!isset($version)) finish();
  if (!isset($bundle)) finish();
  if (!isset($lang)) finish();
  
  // load json with data
  $jsonString = file_get_contents("gc.json");
  if (!$jsonString || $jsonString == "") finish();
  
  $json = json_decode($jsonString, true);
  
  if (!$json[strtolower($bundle)]) finish();
  
  $jsonBundle = $json[strtolower($bundle)];
  if (!$jsonBundle[$version]) finish();
  
  $jsonVersion = $jsonBundle[$version];
  if (!$jsonVersion[$lang] && !$jsonVersion["default"]) finish();

  $returnData = array();
  
  // get the default values, if present
  if ($jsonVersion["default"]) {
    $jsonDefaultLang = $jsonVersion["default"];
    foreach ($jsonDefaultLang as $key => $val) {
      $returnData[$key] = $val;
    }
  }

  // get the language specific values and overwrite the default values
  if ($jsonVersion[$lang]) {
    $jsonLang = $jsonVersion[$lang];
    foreach ($jsonLang as $key => $val) {
      $returnData[$key] = $val;
    }
  }
  
  $x = new record_item ( ); // start plist with record
  
  foreach ($returnData as $key => $val) {
    if (is_bool($val)) {
      $x->add_bool($key, $val); // add bool value
    } else if (is_int($val)) {
      $x->add_int($key, $val); // add integer value
    } else if (is_string($val)) {
      $x->add_text($key, $val); // add string value
    }
  }
  
  print $x; // display the property list.

?>