Question

I’m using chcsvparser to parse data from a csv file on my apps launch. It’s taking way too long to startup on main thread so I was thinking of doing this on the background thread. But I read that you can’t pass objects between the threads. The parser outputs an NSArray so is there a way to do this? I’ve also read that you shouldn’t change UI from background thread but this array will load a table view.

Answer 1

The NSObject class has several different instance methods that allow you to invoke methods on the main UI thread. The performSelectorOnMainThread:withObject:waitUntilDone: method, for instance, allows you to invoke a method of the receiver on the main thread with the object of your choice.

Here’s some code to get you started:

-(void) dataDoneLoading:(id) obj {
    NSMutableArray *array = (NSMutableArray *) obj;
    // update your UI
    NSLog(@"done");
}

-(void) myThread:(id) obj {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSMutableArray *array = [[[NSMutableArray alloc]init ]autorelease];

    // build up your array

    [self performSelectorOnMainThread:@selector(dataDoneLoading:) withObject:array waitUntilDone:NO];

    [pool release];    
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    [NSThread detachNewThreadSelector:@selector(myThread:) toTarget:self withObject:nil];    
}