NSUserDefaults will not load after leaving app - objective-c

Question

I set up multiple NSUserDefaults in my app that work for the most part. The NSUserDefaults are called from one ViewController and implemented at another (such as in a game with a level select). This seems to work well, until the user presses the back button on the level select screen. When they try to go back to the level select viewController, the NSUserDefaults are not loaded onto the screen.
Here is my code:
LevelSelectViewController:
- (void)viewDidLoad
{
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[userDefaults synchronize];
[super viewDidLoad];
}
- (void)Level1DidFinish:(Level1 *)controller
{
[self dismissModalViewControllerAnimated:YES];
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSInteger rank = [userDefaults integerForKey:#"levelRank"];
{
if (rank == 1) {
button2.hidden = NO;
}
}
}
Level1ViewController:
{
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[userDefaults setInteger:1 forKey:#"levelRank"];
}

Answer 1

You need to call [userDefaults synchronize] after setting a value for a key. The automatic synchronization happens quite rarely, so in this case, while one completes a level, the sync won't have yet happened.
So modify your code like this:
Level1ViewController:
{
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[userDefaults setInteger:1 forKey:#"easyRank"];
[userDefaults synchronize];
}

Answer 2

Your first issue is you are creating an instance of userDefaults, but are not setting any values. So calling synchronize here is actually doing nothing:
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[userDefaults synchronize];
After you set a your Integer, then you need to call synchronize:
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[userDefaults setInteger:1 forKey:#"easyRank"];
[userDefaults synchronize];

Answer 3

You're setting values for two different keys. What are you expecting to happen?
Either Level1ViewController needs to set a value for levelRank or LevelSelectViewController needs to read the value for the easyRank key.