NSUserDefaults written in -applicationWillTerminate: do not take effect; What for?

Question

I put the code inside my AppDelegate, but when I started the application again, I noticed that the values ​​are still persistent (not NULL). Why is this?

Code:

- (void)applicationWillTerminate:(UIApplication *)application { [[NSUserDefaults standardUserDefaults] setObject:NULL forKey:@"roomCat"]; [[NSUserDefaults standardUserDefaults] setObject:NULL forKey:@"TFA"]; [[NSUserDefaults standardUserDefaults] setObject:NULL forKey:@"comments"]; } 

Thanks.

Answer 1

Instead of NULL you should use -removeObjectForKey: The former is the official way to remove values, and the latter is undocumented behavior.

In any case, if using -removeObjectForKey: does not work, you can add a call

 [[NSUserDefaults standardUserDefaults] synchronize]; 

in the end. But just do it if it doesn't work without him. The reason is that the -synchronize call -synchronize (relatively) expensive, so it needs to be done only when necessary to ensure correctness.

---

After another look, I suspect that your real problem is that this method is not called at all. On iOS 4 and later, when applications enter the background, they do not call this method, instead they call -applicationDidEnterBackground: Instead, you should try putting this code.

Answer 2

In this case, I expect that you will need to manually call the synchronization method in NSUserDefaults as the last line in this method to make sure that it synchronizes before the application terminates.

Answer 3

try this method:

 - (void)removeObjectForKey:(NSString *)defaultName 

Answer 4

  NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults]; if (prefs) { [prefs setObject:NULL forKey:@"roomCat"]; [prefs synchronize]; }