应用终止时从NSUserDefaults清除数据

Question

Once I kill application then I want to Clear data from NSUserDefaults, but sometimes it is not getting cleared. I have added the code into this method :

- (void)applicationWillTerminate:(UIApplication *)application {
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    [[NSUserDefaults standardUserDefaults]removeObjectForKey:kcoupondic];

    [[NSUserDefaults standardUserDefaults] synchronize];
}

Answer 1

Why are you using NSUserDefaults if you want to clear values on app termination.

Use global variable instead of NSUserDefaults

OR

If you wan't to remove all NSUserDefaults try this:

[[NSUserDefaults standardUserDefaults] removePersistentDomainForName:[[NSBundle mainBundle] bundleIdentifier]];

Answer 2

applicationWillTerminate is not always called. This is from Apple's documentation.

This method lets your app know that it is about to be terminated and purged from memory entirely. You should use this method to perform any final clean-up tasks for your app, such as freeing shared resources, saving user data, and invalidating timers. Your implementation of this method has approximately five seconds to perform any tasks and return. If the method does not return before time expires, the system may kill the process altogether. For apps that do not support background execution or are linked against iOS 3.x or earlier, this method is always called when the user quits the app. For apps that support background execution, this method is generally not called when the user quits the app because the app simply moves to the background in that case. However, this method may be called in situations where the app is running in the background (not suspended) and the system needs to terminate it for some reason.

To answer your question as to why your data is not getting cleared, maybe this method is not getting called. Try and add some logs to check if the method gets called.

I would rather put this code in applicationDidFinishLaunchingWithOptions inside AppDelegate. In this case, you're sure that at every app launch you'll clear this data before you re-populate it.

Answer 3

For Swift:

if let bundleId = Bundle.main.bundleIdentifier {
    UserDefaults.standard.removePersistentDomain(forName: bundleId)
}

Here, we are optional unwrap bundleIdentifier to prevent crash.

Answer 4

尝试编写代码以清除applicationWillResignActive而不是applicationWillTerminate NSUserDefaults。