Our existing system was designed when land line phones dominated before cell phones were even heard of, at least to the general public.

In the intervening years, cell phone service, and later Voice Over IP (VOIP) or internet phones have been scabbed into the system with some hacks. Good hacks, but they are still hacks. The Next Generation system that the National Emergency Number Association (NENA) has defined will provide a more solid and extensible base for handling the existing system and future growth, including text messages, photos, videos and other sources of information that our mobile communications make possible that can help the emergency responders be better prepared for the situation at hand.

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Development, TCS

Could I have discovered a bug in Core Data?

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iPhone, Core Data, iOS

The error:

2011-07-09 16:57:36.670 Sound-Church[12292:207] Unresolved error Error Domain=NSCocoaErrorDomain Code=256 “The operation couldn’t be completed. (Cocoa error 256.)” UserInfo=0x4d62010 {NSFilePath=/Users/john/Library/Application Support/iPhone Simulator/4.3.2/Applications/BF78B117-48CA-48C7-A61E-29A452E2824A/Documents/Sound_Church.sqlite, NSUnderlyingException=error during SQL execution : constraint failed}, {
NSFilePath = “/Users/john/Library/Application Support/iPhone Simulator/4.3.2/Applications/BF78B117-48CA-48C7-A61E-29A452E2824A/Documents/Sound_Church.sqlite”;
NSUnderlyingException = “error during SQL execution : constraint failed”;
}

I see the error from this code:


- (void)saveContext

{

   NSLog(@"Entering saveContext");


   NSError *error = nil;

   NSManagedObjectContext *managedObjectContext = self.managedObjectContext;

   if (managedObjectContext != nil)

   {

     if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error])

     {

       NSLog(@"Unresolved error %@, %@", error, [error userInfo]);

       abort();

     }

   }

}



In searching the web, I found this article that talks about that very message, but it doesn’t seem to apply as apparently the writer is directly accessing the sqlite database, which I don’t do.

I also found this question and answer, which suggests a possible problem, but again, I don’t see it applying to me, as I use a NSFetchedResultsController to populate the UITableView and otherwise only fetch results to verify that the new Item is unique.

The code where I fetch results to check for an error:

- (void)parser:(NSXMLParser *)parser

didEndElement:(NSString *)elementName

namespaceURI:(NSString *)namespaceURI

qualifiedName:(NSString *)qName

{

   if (!self.currentItemObject)

   {

     // We don't want to bother attempting to process all the header info.

     return;

   }



   if ([elementName isEqualToString: kItemElementName])

   {

     NSPredicate *predicate = [NSPredicate predicateWithFormat: @"guid == \"%@\"", currentItemObject.guid];

     NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];

     [request setPredicate: predicate];

     NSEntityDescription *entity = [NSEntityDescription entityForName:@"Item"

    inManagedObjectContext:self.context];

     [request setEntity: entity];

     NSError *error = [[[NSError alloc] init] autorelease];

     NSMutableArray *items = [[context executeFetchRequest: request error: &error] mutableCopy];

     if (!items)

     {

       // TODO: Need to do better error handling.

       NSLog(@"Error fetching items. %@", [error localizedDescription]);

       [items release];

       return;

     }



     if (0 < [items count])

     {

       // This is a duplicate element, we don't want to save it.

       [items release];

       return;

     }



     [items release];

...


At this point, I haven’t resolved this issue, so I’m still looking for a solution.

In the process of digging through the code, I did stumble upon another problem. I found that the title of the podcasts seemed to always be the same as the summary. So I did some digging, and found that, in fact, I was not copying the data elements into the NSManagedObject. Dumb.. Since the objects (NSStrings in this case) are passed as pointers, when I would write the next string into the same NSMutableString, it overwrote the previous entry, so all elements of an object became the last thing I entered.

So that’s solved, but I’m going to have to do some more digging into the sqlite table to figure out the problem with the error.

I have an image of the screen. Not really exciting, especially since it seems to be loading the one item multiple times, and that one item is the lone video in the package.

I’m thinking I’ll break the connection I have between the Channel object and the Item objects. The connection is somewhat arbitrary, and I’m not even sure I need the channel, but I have it for now. I certainly don’t need the connection to the channel.

Latest code has been uploaded to github (github account required), for anyone who’s interested to look at it.

Instead, you need to use the NSEntityDescription class method


+ (id)insertNewObjectForEntityForName:(NSString *)entityName

inManagedObjectContext:(NSManagedObjectContext *)context;


This method returns a NSManagedObject of the type noted by the entityName parameter.

While dealing with all this stuff. I realized I don’t understand all the in’s and out’s of how the model creates objects. I had the model backwards, as the one Channel contains many Items, but the model reversed that, so I had to pull some hackery to get what I want.

One little key, if you modify the model, you’ll have to delete the files in ~/Library/Application Support/iPhone Simulator/<version>/Applications/. I deleted everything in there and it was happy again.

At this point, I’m getting data into the model, and that’s good enough for now. I still need to deal with new vs. existing entries, but that’s for another time. It’s now time to move on to the RootViewController and start displaying the data available.

I have a class, RSSDownloader, that implements the NSURLConnection protocol. It also has a delegate that handles the output, providing a bit of abstraction for the connections. When the application launches, the downloader will download the xml file from the RSS feed server and parse it. Then when the user wants to listen to a podcast, that podcast needs to be downloaded, so the RSSDownloader will be used again.

I’m currently working on the parser, which parses the xml file into the required objects. Currently it’s failing on the title of the Channel object. In the current data definition, the channel contains the data that’s part of the RSS header. It contains a list of Items, each item being a separate podcast.

I’d do a screenshot of the data model, but Xcode 4 seems to spread the model out over more than one screen, even though there’s only two entities, and I can’t seem to figure out how to move them closer together, or if it’s possible.

Notice the -ObjC -all_load flags. Those are required to load a static library, as the dynamic nature of Objective-C makes it not load those libraries.

I’m still figuring out how to use a fake method with multiple parameters with this tool, however. The available documentation is a bit light. I did find this post, which is about the best I’ve found for using OCMock. Nobody describes using OCMock with Xcode 4, however.

For iOS, look in ~/Library/Application Support/iPhone Simulator/ where version is the iOS version you are targeting to find the offending files. I just blew away all the sub-folders in that folder to solve my problem.