CHCSVParser in the main thread

Question

Hello all,

This is a follow-up to a previous post regarding the CHCSVParser from Dave DeLong. In short, I am using the CHCSVParser to work with an extremely large CSV file and parse the lines into Core Data entities (on an iPhone). I've got the parser hooked up and working, and am now trying to display a progress indicator to the user.

I ask the app's user to provide a name for the list to be imported with a modal view controller, but the problem I am running into is that the screen looks "stuck" while the parser is running and the modal VC appears frozen (looks like it's not dismissed). No matter how I arrange the code, it seems that the parser is locking everything up while it runs, so the modal VC doesn't get animated out and the progress indicator (a simple UIView and UILabel) is hidden.

I've never programmed with threads before, but this sounds kinda thready to me. How can I address this?

Thanks!

the code:

==== CALLBACK METHOD FROM THE MODAL VC ====

//
// Dismiss the modal VC
//
[self dismissModalViewControllerAnimated:NO];

//
// Set up the progress indicator view
//
progressView = [[UIView alloc] initWithFrame:CGRectMake(0,0,320,480)];
progressView.backgroundColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:.9];

UILabel *progressLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 150, 300, 60)];
progressLabel.backgroundColor = [UIColor clearColor];
progressLabel.textAlignment = UITextAlignmentCenter;
progressLabel.tag = 12345;
progressLabel.text = NSLocalizedString(@"Beginning import...",@"");
progressLabel.textColor = [UIColor whiteColor];
[progressView addSubview:progressLabel];

[self.view addSubview:progressView];

//
// If a name was provided, then create a List with the given name then parse the
// selected CSV file into it
//
if (listName != nil) {
    // Create the new List object and set the currentList to point to it.
    NSError *error = nil;
    NSEntityDescription *ed = [NSEntityDescription entityForName:@"FOList" inManagedObjectContext:managedObjectContext];
    FOList *theList = [NSEntityDescription insertNewObjectForEntityForName:[ed name] inManagedObjectContext:managedObjectContext];
    theList.name = listName;
    if (![managedObjectContext save:&error]) {
        NSLog(@"Error saving the new list! %@ %@", [error localizedDescription], [error userInfo]);
    }
    currentList = theList;

    //
    // Grab the appropriate file
    //
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSURL *inputFileURL = [NSURL fileURLWithPath: [documentsDirectory stringByAppendingPathComponent:selectedFileName]];

    //
    // Start the parsing
    //
    NSStringEncoding encoding = 0;
    CHCSVParser *p = [[CHCSVParser alloc] initWithContentsOfCSVFile:[inputFileURL path] usedEncoding:&encoding error:nil];
    [p setParserDelegate:self];
    numRowsParsed = [NSNumber numberWithInt:0];
    [p parse];
    [p release];

Answer 1

Perfect job for NSOperation or NSInvocationOperation.

Answer 2

Answered my own question here. After a bit of digging I found a good article here. NSOperationQueues were a bit overkill here, and all I needed were the methods – performSelectorInBackground:withObject: and – performSelectorOnMainThread:withObject:waitUntilDone:. These methods will handle the background and main threads for you and make it easy as pie!