更新UILabel返回Null吗？

Question

I'm trying to update a label that display the amount of coins, stored in NSUserDefaults .

I have a method called updateCoins which I call when I have added, coins based on user activity, to update the UILabel :

- (void)updateCoins {
    self.coinsLabel.text = 
     [NSString stringWithFormat:@"%d", 
       [[[NSUserDefaults standardUserDefaults] objectForKey:@"Coins"] intValue]];
    NSLog(@"Label: %@", self.coinsLabel.text);
    NSLog(@"Coins: %d", 
       [[[NSUserDefaults standardUserDefaults] objectForKey:@"Coins"] intValue]);
}

However in the logger, I get the following:

Label: (null)
Coins: 10

The thing is when, I call this method in viewWillAppear , it updates the app, when transitioning to a different UIViewController and coming back.

If it helps I'm updating the object the following way:

int coins;
coins = [[[NSUserDefaults standardUserDefaults] objectForKey:@"Coins"] intValue];
[[NSUserDefaults standardUserDefaults] setObject:
  [NSString stringWithFormat:@"%d",coins+10] forKey:@"Coins"];
[[NSUserDefaults standardUserDefaults] synchronize];
[self updateCoins];

Answer 1

self.coinsLabel.text = // replace this with self.treeCoinsLabel.text
 [NSString stringWithFormat:@"%d", 
  [[[NSUserDefaults standardUserDefaults] objectForKey:@"Coins"] intValue]];
NSLog(@"Label: %@", self.treeCoinsLabel.text);

Also if your self.coinsLabel is an outlet, verify that it's correctly connected on the user interface, if not you must allocate it before use it.

Answer 2

Hopefully, you are assigning the value to the self.coinsLabel.text before its get allocated (pointer which holds other custom UILabel) , that's why it gets updated when come back from the child UIViewController.

Ensure that the UILabel has allocated before assign the value to it. you might calling this function before the View gets loaded.

Answer 3

There are two possibilities in this situation.

self.coinsLabel is null and not initialized. If self.coinsLabel = [[UILabel alloc] init]; doing this in - (void)viewDidLoad is still nill then you should check Is it connected from storyboard to class? .

Answer 4

- (void)viewDidLoad:animated
{
    [super viewDidLoad:animated];
    self.coinsLabel = [[UILabel alloc] init];
}

I guess you forget initializing UILabel.