Question

I am relatively new to Objective-C and now I have a problem in my iPhone app that I don’t fully understand.
I try to use a NSMutableDictionary, this does not seem to work as i expect for some reason. When I run the debugger and do po numberToCallerMap to see the dictionary, I get an exception. I have read the documentation for NSMutableDictionary on how to initialize it, but I can not see what I am doing wrong. Help and advice are appreciated. The variable causing me problem is numberToCallerMap, here is the relevant function:

- (void)setData:(NSString*)value{
[list release];
list = [[NSMutableArray alloc] init];
SBJSON *json = [[[SBJSON alloc] init] autorelease];
NSMutableDictionary* numberToCallerMap;
CallerInfo* caller;
NSDictionary* callerInfo;

@try {      
    NSArray *array = (NSArray*)[json objectWithString:value];       
    // reading all the items in the array one by one  
    numberToCallerMap = [NSMutableDictionary dictionary];

    for (id *item in array) {  

        // if the item is NSDictionary (in this case ... different json file will probably have a different class)  
        NSDictionary *dict2 = (NSDictionary *) item;  
        CallInfo *data = [CallInfo alloc];           
        [data initFromDictionary:dict2];


        callerInfo = (NSDictionary*)[dict2 valueForKey:@"caller"] ;

             //Here, we want the phonenumber to be part of the CallerInfo object instead.
             // It is sent from the server as part of the Call-object
        NSString* number = (NSString*)[dict2 valueForKey:@"phoneNumber"];
        [callerInfo setValue:number forKey:@"phoneNumber"];

        caller = (CallerInfo*)[numberToCallerMap valueForKey:number];
        if(caller == nil || [caller isKindOfClass:[NSNull class]]){
            caller = [CallerInfo alloc];
            [caller initFromDictionary:callerInfo];

            [numberToCallerMap setValue:caller forKey:number];  
            [list insertObject:caller atIndex:0];
            }
        [caller addRecentCall:data];            
     } 
}
@catch (NSException * e) {
    [list release];
    list = [[NSMutableArray alloc] init];
}
@finally {
    [numberToCallerMap release];
}
}

Answer 1

This is probably not the only problem, but you are not alloc-ing your numberToCallerMap dictionary, you are getting it from a convenience class method — [NSMutableDictionary dictionary] — that returns it autoreleased. So you should not call release on it yourself.