Delete all my NSUserDefaults that start with a certain word

Question

Is there a way for me to "walk" through a list of all the NSUserDefaults in my iPhone app, and only delete certain ones?

For example, I'd like to get all the key names that start with a certain word.

Something like this:

[[NSUserDefaults standardUserDefaults] removeObjectForKey:@"Dog*"];

Answer 1

You can look through the dictionaryRepresentation.

Here's an implementation which uses NSPredicate as a generic matcher for greater flexibility.

@interface NSUserDefaults (JRAdditions)
- (void)removeObjectsWithKeysMatchingPredicate:(NSPredicate *)predicate;
@end

@implementation NSUserDefaults (JRAdditions)

- (void)removeObjectsWithKeysMatchingPredicate:(NSPredicate *)predicate {
   NSArray *keys = [[self dictionaryRepresentation] allKeys];
   for(NSString *key in keys) {
      if([predicate evaluateWithObject:key]) {
         [self removeObjectForKey:key];
      }
   }
}

@end

Usage:

NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF BEGINSWITH %@", @"something"];
[[NSUserDefaults standardUserDefaults] removeObjectsWithKeysMatchingPredicate:pred];