Question

I am having trouble saving an NSMutableDictionary. I am trying to save it to NSUserDefaults, then load and change a blue, then save it again.

So I initially make it like so:

NSMutableDictionary *d = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                              firstNameLbl, @"firstName",
                              lastNameLbl, @"lastName", 
                              nil];
    [[NSUserDefaults standardUserDefaults] setObject:d forKey:@"youDict"];
    [[NSUserDefaults standardUserDefaults] synchronize];

Then I load it and try and change a value like this:

NSMutableDictionary *d = [[NSUserDefaults standardUserDefaults] objectForKey:@"youDict"];
    [d setObject:textField.text forKey:key];
    [[NSUserDefaults standardUserDefaults] setObject:d forKey:@"youDict"];
    [[NSUserDefaults standardUserDefaults] synchronize];

However, this line, [d setObject:textField.text forKey:key];, causes the app to crash and I get this error:

'NSInternalInconsistencyException', reason: '-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object'

Answer 1

objectForKey returns an immutable value for NSUserDefaults. To make this work replace the first line of your 2nd code block with this:

 NSMutableDictionary *d = [NSMutableDictionary dictionaryWithDictionary: [[NSUserDefaults standardUserDefaults] objectForKey:@"youDict"]];