What can cause NSUserDefaults to be cleared

Question

I've been getting some odd reports for my app where the application settings stored into the NSUserDefaults is being cleared. The reports have all been on iOS 7s

I know you can manually clear the NSUserDefaults by either uninstalling or making a call to

NSString *appDomain = [[NSBundle mainBundle] bundleIdentifier];

[[NSUserDefaults standardUserDefaults] removePersistentDomainForName:appDomain];

But are there any other known causes for an app to clear its settings ?

Answer 1

If you don't want to get your data deleted, then you should use KeyChain to store values. A good way to get started: Using KeyChain

Below I am providing an example code how to store and get data back from the KeyChain

Importing required frameworks

#import <Security/Security.h>

Storing values to KeyChain

NSString *key = @"Full Name";
NSString *value = @"Steve Jobs";
NSData *valueData = [value dataUsingEncoding:NSUTF8StringEncoding];
NSString *service = [[NSBundle mainBundle] bundleIdentifier];
NSDictionary *secItem = @{
                              (__bridge id)kSecClass : (__bridge id)kSecClassGenericPassword, (__bridge id)kSecAttrService : service,
                              (__bridge id)kSecAttrAccount : key,
                              (__bridge id)kSecValueData : valueData,
                              };
    CFTypeRef result = NULL;
    OSStatus status = SecItemAdd((__bridge CFDictionaryRef)secItem, &result);
if (status == errSecSuccess)
{
     NSLog(@"Successfully stored the value");
}
else{
     NSLog(@"Failed to store the value with code: %ld", (long)status);
}

Getting values back from KeyChain

NSString *keyToSearchFor = @"Full Name";
NSString *service = [[NSBundle mainBundle] bundleIdentifier];
NSDictionary *query = @{
                        (__bridge id)kSecClass : (__bridge id)kSecClassGenericPassword, (__bridge id)kSecAttrService : service,(__bridge id)kSecAttrAccount : keyToSearchFor,
                        (__bridge id)kSecReturnAttributes : (__bridge id)kCFBooleanTrue, };
CFDictionaryRef valueAttributes = NULL;
OSStatus results = SecItemCopyMatching((__bridge CFDictionaryRef)query,
                                       (CFTypeRef *)&valueAttributes);
NSDictionary *attributes =
(__bridge_transfer NSDictionary *)valueAttributes;
if (results == errSecSuccess){
    NSString *key, *accessGroup, *creationDate, *modifiedDate, *service;
    key = attributes[(__bridge id)kSecAttrAccount];
    accessGroup = attributes[(__bridge id)kSecAttrAccessGroup]; creationDate = attributes[(__bridge id)kSecAttrCreationDate]; modifiedDate = attributes[(__bridge id)kSecAttrModificationDate]; service = attributes[(__bridge id)kSecAttrService];
    NSLog(@"Key = %@\n \ Access Group = %@\n \
          Creation Date = %@\n \
          Modification Date = %@\n \
          Service = %@", key, accessGroup, creationDate, modifiedDate, service);
}
else
{
    NSLog(@"Error happened with code: %ld", (long)results);
}