CODEWITHSUNDEEP
objective-cnsmutabledictionary
Andrey Chernukha
Andrey Chernukha

Reputation: 21808

Weird behaviour of NSMutableDictionary

Take a look at this piece of code

- (NSMutableDictionary *)getUsersFromServer
{
//here we're getting list of users from the server
NSMutableDictionary * users = [[[NSMutableDictionary alloc] init] autorelease];

userresults = [[NSMutableArray alloc] init];    

//all this will be replaced with users taken from the server. it's needed just for testing
for (int i = 0;i < 19;i++)
{

    int wins    = i ;         float f_wins = (float)wins;
    int losses  = i * 2 ;     float f_losses = (float)losses;
    int withdr  = i * 3 ;     float f_withdr = (float)withdr;
    float win_per = f_wins / ((f_wins + f_losses + f_withdr) / 100.0);

 [userresults setArray:[NSMutableArray arrayWithObjects:[NSNumber numberWithInt:wins],
                                                                                [NSNumber numberWithInt:losses],
                                                                                [NSNumber numberWithInt:withdr],
                                                                                [NSNumber numberWithFloat:win_per],
                                                                                 nil]]; 
[users setObject:userresults forKey:[NSString stringWithFormat:@"user number %i",i]];

}

[userresults release];
return users;
}

in each loop iteration i fill array with numbers and set it as value into NSMutableDictionary. As a key for each array serves formatted string which is unique by number of iteration counter. So... the problem is - the dictionary is always filled with SAME arrays for DIFFERENT keys. There are 19 arrays in the dictionary and ALL THEY ARE LAST ONES!!!! That is from the last iteration. And each one has different key!!! How could it happen??? What's going on???

Upvotes: 0

Views: 62

Answers (2)

Cliff
Cliff

Reputation: 11238

userresults is declared outside the loop unnecessarily. You can forego mutable arrays here and just create a new NSArray with each iteration. Your problem stems from reusing the array declared outside the loop and putting new values in each time. Try this:

[users setObject: [NSArray arrayWithObjects:[NSNumber numberWithInt:wins], [NSNumber numberWithInt:losses], [NSNumber numberWithInt:withdr], [NSNumber numberWithFloat:win_per], nil];
[users setObject:userData forKey:[NSString stringWithFormat:@"user number %i",i]]
forKey:[NSString stringWithFormat:@"user number %i",i]];;

Upvotes: 0

mipadi
mipadi

Reputation: 410662

userresults points to the same object, and you're modifying that same array with the setArray: method. Create a new array in each loop iteration instead:

NSArray *userData = [NSArray arrayWithObjects:[NSNumber numberWithInt:wins],
                                              [NSNumber numberWithInt:losses],
                                              [NSNumber numberWithInt:withdr],
                                              [NSNumber numberWithFloat:win_per],
                                              nil];
[users setObject:userData forKey:[NSString stringWithFormat:@"user number %i",i]];

Upvotes: 3

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