Strange output when trying to access data

Question

I have a data structure object which is loaded from an XML file inside the "did finish loading" method of the delegate.

If I use the data objects "printData" method from inside the load method of the delegate it shows all the info. I can do this multiple times.

However, I have a button which runs a second method in the delegate and all this does is run the printData method of my data object but all I get is either nothing or some random property text.

e.g. "UIDeviceFamily" or "ar.lproj" etc...

Once this has printed it crashes the app with an "EXC_BAD_ACCESS" error.

I remember there being a directory to look into find more details of this error but I can't remember which one it is.

Thanks for any help you can provide.

Sorry, this is the code that matters in the app...

This is the code that populates the data.

    -(id)initMapFromXMLData:(NSData *)xmlData
{
    if (self = [super init])
    {
        MapXMLParser *parser = [[MapXMLParser alloc] initWithData:xmlData];
        [parser setDelegate:parser];
        [parser parse];

        statementPairs = [NSDictionary dictionaryWithDictionary:parser.statementPairs];
        prefPairs = [NSDictionary dictionaryWithDictionary:parser.prefPairs];
        clusters = [NSDictionary dictionaryWithDictionary:parser.clusters];

        /*
        statementPairs = parser.statementPairs;
        prefPairs = parser.prefPairs;
        clusters = parser.clusters;
        [parser release];*/
    }
    return self;
}

This then gets run from the delegate...

NSData *xmlData;

xmlData = [[NSData alloc] initWithContentsOfFile:@"/Users/oliver/Documents/XCode stuff/Saviio/Saviio 2/Saviio/Classes/Statements"];

myMap = [[Map alloc] initMapFromXMLData:xmlData];

And then in the same delegate method I display it...

[myMap printClusters];

... which runs...

-(void)printClusters
{
    NSLog(@"Printing Clusters for %@", self);

    for (int i = 1; i <= [clusters count]; i++)
    {
        Cluster *tempCluster;

        tempCluster = [clusters objectForKey:[NSString stringWithFormat:@"%d", i]];

        NSLog(@"Cluster %@", tempCluster.name);

        for (int j = 0 ; j < [tempCluster.fgids count]; j++)
        {
            Preference *tempPref;

            tempPref = [prefPairs objectForKey:[[tempCluster.fgids objectAtIndex:j] stringValue]];

            NSLog(@"Pref ---> %@/%@", tempPref.left, tempPref.right);

            for (int k = 0 ; k < [tempPref.qids count]; k++)
            {
                Statement *tempStat;

                tempStat = [statementPairs objectForKey:[[tempPref.qids objectAtIndex:k] stringValue]];

                NSLog(@"Stat -------> %@ - %@", tempStat.left, tempStat.right);
            }
        }
    }

    NSLog(@"END");
}

This all works fine.

However, when I then run the same method [myMap printClusters] from a method that runs from a button press in the delegate then it prints the first line... "Printing clusters for ".

And then the strange line and then crash.

Answer 1

It appears that clusters is a property of self but you never retain it. Since it is created with a convenience method that returns an autoreleased dictionary it is released when the methods scope completes. When you call it a second time, it is not alive any longer.

Change:

clusters = [NSDictionary dictionaryWithDictionary:parser.clusters];

...to:

self.clusters = [NSDictionary dictionaryWithDictionary:parser.clusters];

...or:

clusters = [[NSDictionary dictionaryWithDictionary:parser.clusters] retain];

... and then change all other references to clusters to self.clusters. Do the same for any other properties.

Answer 2

Well, following the advice of TechZen I had a look at the code that was populating the NSDictionary and found that I was storing the pointed parser variables.

Instead I changed them to allocate its own variables and store them instead.

That sorted it.

Woo!

Old code...

-(id)initWithName:(NSString *)inputName
{
    if (self = [super init])
    {
        name = inputName;
        fgids = [[NSMutableArray alloc] initWithCapacity:1];
    }
    return self;
}

New code...

-(id)initWithName:(NSString *)inputName
{
    if (self = [super init])
    {
        self.name = [NSString stringWithString:inputName];
        self.fgids = [[NSMutableArray alloc] initWithCapacity:1];
    }
    return self;
}

Woo!