Question

Assume I have 3 files in my project:

1. data model file, dealing with Core Data and fetching info
2. viewController 1
3. viewController 2

In the model file I get results us follows:

- (NSArray *) getColonyData
{
NSManagedObjectContext *cxt = [self managedObjectContext];
NSEntityDescription *colonyDesc = [NSEntityDescription entityForName:@"Colony" inManagedObjectContext:cxt];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:colonyDesc];

NSError *error;
NSArray *colonyResults = [cxt executeFetchRequest:request error:&error];

return colonyResults;
}

I run this part of code in viewDidLoad section of the 1st viewController and I get proper results:

  NSArray *colonyResults = [model getColonyData];
    if (colonyResults != nil)
    {
        colonyName.text = [[colonyResults objectAtIndex:0] valueForKey:@"name"];
    }
    else
    {
        colonyName.text = @"nothing setup yet";
    }

Then I move via a segue to a 2nd viewController, when I execute exactly same code (of course updating different UI elements). But this time the result is nil. What am I doing wrong here? Should I release results manually first? No other errors appear.
Thanks.

Answer 1

As suggested in comments:

experimentModel *model; doesn’t assign anything; it just declares that a variable exists. Somewhere, you must be setting model to an actual object for the first controller (and probably not doing that for the second one).

Sending messages to nil objects is a common way to not get the results one was expecting. 🙂