Ios – iphone keychain items persist after application uninstall

iOS 3.2 and later support this. Straight from the What's New in iPhone OS 3.2 doc:

Custom Font Support
Applications that want to use custom fonts can now include those fonts in their application bundle and register those fonts with the system by including the UIAppFonts key in their Info.plist file. The value of this key is an array of strings identifying the font files in the application’s bundle. When the system sees the key, it loads the specified fonts and makes them available to the application.

Once the fonts have been set in the Info.plist, you can use your custom fonts as any other font in IB or programatically.

There is an ongoing thread on Apple Developer Forums:
https://devforums.apple.com/thread/37824 (login required)

And here's an excellent and simple 3 steps tutorial on how to achieve this (broken link removed)

1. Add your custom font files into your project using Xcode as a resource
2. Add a key to your Info.plist file called UIAppFonts.
3. Make this key an array
4. For each font you have, enter the full name of your font file (including the extension) as items to the UIAppFonts array
5. Save Info.plist
6. Now in your application you can simply call [UIFont fontWithName:@"CustomFontName" size:12] to get the custom font to use with your UILabels and UITextViews, etc…

Also: Make sure the fonts are in your Copy Bundle Resources.

You can take advantage of the fact that NSUserDefaults are cleared by uninstallation of an app. For example:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //Clear keychain on first run in case of reinstallation
    if (![[NSUserDefaults standardUserDefaults] objectForKey:@"FirstRun"]) {
        // Delete values from keychain here
        [[NSUserDefaults standardUserDefaults] setValue:@"1strun" forKey:@"FirstRun"];
        [[NSUserDefaults standardUserDefaults] synchronize];
    }

    //...Other stuff that usually happens in didFinishLaunching
}

This checks for and sets a "FirstRun" key/value in NSUserDefaults on the first run of your app if it's not already set. There's a comment where you should put code to delete values from the keychain. Synchronize can be called to make sure the "FirstRun" key/value is immediately persisted in case the user kills the app manually before the system persists it.