NSUserDefaults objectForKey keeps returning nil, even when key exists

Question

I'm trying to save data in NSUserDefaults. The very first time this code (and app) loops, it should go through the if-statement. Because no data was saved in NSUserdefaults was saved yet with the names: BoughtItem0, BoughtItem1, BoughtItem2, BoughtItem3.

But somehow after looping the code for the first time, and so starting my app for the second time it keeps going through the if-statement. What's wrong in my code?

for (int i = 0; i < [shopPrices count]; i++)
{
    if ([[NSUserDefaults standardUserDefaults] objectForKey:@"BoughtItem%d"] == nil)
    {
        [[NSUserDefaults standardUserDefaults] setValue:@"NONO" forKey:[NSString stringWithFormat:@"BoughtItem%d", i]];
        NSLog(@"BoughtItem%d", i);
    }
    else
    {
        NSLog(@"No new bought item keys made");
    }
}

the output is:

BoughtItem0
BoughtItem1
BoughtItem2
BoughtItem3

Answer 1

Your problem is that you have used a format string in your call to objectForKey but you have omitted the call to stringWithFormat. I think what you meant was -

for (int i = 0; i < [shopPrices count]; i++)
{
    if ([[NSUserDefaults standardUserDefaults] objectForKey:[NSString stringWithFormat:@"BoughtItem%d",i]] == nil)
    {
        [[NSUserDefaults standardUserDefaults] setValue:@"NONO" forKey:[NSString stringWithFormat:@"BoughtItem%d", i]];
        NSLog(@"BoughtItem%d", i);
    }
    else
    {
        NSLog(@"No new bought item keys made");
    }
}

You had it in the setValue, just not in your if, so you were checking for the existence of the key "BoughtItem%d", but you were setting "BoughtItem0"...