Question

I have a couple questions regarding application preferences using NSUserDefaults.

In my last app I would link my preferences using bindings to NSUserDefaults, and this worked perfectly. In the application startup methods I could then perform actions based on the values stored in the NSUserDefaults.

The problem occured when I updated my application and re-distributed it, in which all the settings would get over-written with the preferences in my computer. So if someone changed the settings, and then received the update, their settings would get over-written with mine.

Looking back at the Apple documentation in regards to saving Preferences, I notice the following line which I didn’t use, which is used to write preferences to disk:

[defaults synchronize];

My question is, does this code write the preferences to the user’s harddrive, so that if I re-distribute the application with different settings, NSUserDefaults will read from the disk instead?

Sorry for the misunderstanding but I can’t find an answer.

Thanks in advance everyone.

Answer 1

If you want to use bindings to control your preferences, you should be using NSUserDefaultsController. In either case, to set initial values for your defaults, you should create a dictionary with the initial values and then pass it to registerDefaults: if you’re using vanilla NSUserDefaults, or one of initWithDefaults:initialValues: or setInitialValues: if you’re using NSUserDefaultsController. Here’s an NSUserDefaultsExample:

- (void)applicationDidFinishLaunching {
    // For decent-sized applications, I normally like to store this in its own plist
    // but I'm creating it in-line here for readability's sake.
    NSDictionary *initialPreferences = [NSDictionary dictionaryWithObjectsAndKeys:
        [NSNumber numberWithInteger:21], @"UserAge",
        @"red", @"FavoriteColor",
        @"Idaho", "Location", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:initialPreferences];
}