Question

I have a NSMutableArray (tripHistory) that gets a NSMutableDictionary (currentUpdate) added to it every second with new data.

[currentUpdate setObject:testVariable forKey:@"Test"];
[tripHistory addObject:currentUpdate];
[currentUpdate removeAllObjects];

Yet when I loop through tripHistory calling [[tripHistory objectAtIndex:i] description] everything is null.

My loop is as follows:

for (int i=0; i<[tripHistory count]; i++)
{
    NSLog(@"%@", [[tripHistory objectAtIndex:i] description]);
}

To initialize my variables, the following code is called only for the first update.

tripHistory = [[NSMutableArray alloc] init];
currentUpdate = [[NSMutableDictionary alloc] init];

Any ideas?

Answer 1

Adding an object to an NSArray doesn’t make a copy of it. All that happens is its reference count is incremented. Therefore currentUpdate and the NSDictionary added to tripHistory are one-and-the-same. If you remove objects from currentUpdate you are also removing objects from the NSDictionary in tripHistory.

After adding currentUpdate to tripHistory all you need to do is release currentUpdate and start again with a new empty NSDictionary for the next update.