Question

I’m working on a project for learning obj-c by building a small application thas talkt to a PHP/MySQL api.

Every time a user does something, a new auth-key is set for this user and is sent to the client. The client receives this value and should set it to NSUserDefaults. This is for not letting the user logon every time the program starts; if this key exsists it will try to authenticate with this key and then login automatically.

This works, some times… I have two functions, one for recieving and one for setting. They looks like this:

//GET
-(NSString*)GetValue:(NSString *)Name
{
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    NSString *get = [prefs stringForKey:Name];

    if(get)
        return get;
    else
        return FALSE;
}
//SET
-(void)SetValue:(NSString*)Name:(NSString*)Value
{
    //Add new...    
    [[NSUserDefaults standardUserDefaults] setObject:Value forKey:Name];    
}

This works, almost.
The problem is like this:

1) The auth-key value is not set (in NSUserDefaults)
2) I try to login the user, the value sets (like “aaaaaaaaaaaaaaaa”) and everything’s fine. I restart the program, it takes this stored value, tries to login, gets a positive result back from PHP along with a new key wich has to be set when the answer returns… like this…

if(NewKey.length > 0)
{
    NSLog(@"TRY SET KEY: %@", NewKey);
    [self SetValue:@"auth_key":NewKey];
    NSLog(@"TRY GET KEY: %@", [self GetValue:@"auth_key"]);
}

3) The NSLog above says “TRY SET KEY: bbbbbbbbbbbbbbbb” and “TRY GET KEY: bbbbbbbbbbbbbbbb”. Looking perfect!
4) Fine, i kill the program and tries again, now it should have stored “bbb…”, right? Wrong! When i now NSLogs this value, it’s still “aaa…”
5) I try login again, the NSLog says “TRY SET KEY: ccc…” and “TRY GET KEY: ccc…” – it says this value is stored. But it’s not…
6) I kill program, restart and gets “aaa…”.
7) I kill program, in the AppDelegate i manually sets this value (With the same function) to like “xxx”. I run the program and it sets the key to something like “xx”. I delete this line, restarts program, the “xxx” is stored properly and now i’m back on #2; I can do one login, it stores this value properly and then i can do one auto-login but on that login it stops saving it…

So, what is wrong here? I’ve tried [[NSUserDefaults standardUserDefaults] removeObjectForKey:Name]; as first line in SetValue but it does not helps.

It is like it sets, and then beeing forgotten anyway… What am i doing wrong?

Answer 1

NSUserDefaults doesn’t write the changes to file at the moment when you set a value. It does so periodically, once in a while. If you want it to immediately persist the changes to disk, you should synchronize it:

[[NSUserDefaults standardUserDefaults] setObject:Value forKey:Name];
[[NSUserDefaults standardUserDefaults] synchronize];