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POiOS CoreData Background Thread Fetching in cellForRowAtIndexPath
 

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  1. POiOS CoreData Background Thread Fetching in cellForRowAtIndexPath
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    <p>I have a tableview in my app that contains a NSFetchedResultsController to load in some CoreData objects.</p> <p>As the table builds in <code>cellForRowAtIndexPath:</code>, for each cell I must do a fetch to get some other info from another object. </p> <p>The table is filled with UserTasks, and I must get some info from a UserSite (UserTask contains a siteID attribute)</p> <p>I am getting the UserSite info in a background thread, and using a temporary context. It works fine, but it still wants to lag the UI a bit when scrolling.</p> <pre><code> Site *site = [_scannedSites objectForKey:task.siteID]; if(!site) { dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ AppDelegate *ad = [AppDelegate sharedAppDelegate]; NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSConfinementConcurrencyType]; temporaryContext.persistentStoreCoordinator = ad.persistentStoreCoordinator; Site *site2 = [task getSiteWithContext:temporaryContext]; if(site2) { [ad.managedObjectContext performBlock:^{ Site *mainContextObject = (Site *)[ad.managedObjectContext objectWithID:site2.objectID]; [_scannedSites mainContextObject forKey:task.siteID]; }]; dispatch_async(dispatch_get_main_queue(), ^{ Site *newSite = [_scannedSites objectForKey:task.siteID]; cell.lblCustName.text = newSite.siteName; cell.lblAddr.text = [NSString stringWithFormat:@"%@ %@, %@", newSite.siteAddressLine1, newSite.siteCity, newSite.siteState]; cell.lblPhone.text = [self formatPhoneNum:newSite.phone]; }); } else { dispatch_async(dispatch_get_main_queue(), ^{ cell.lblCustName.text = @""; cell.lblAddr.text = @""; cell.lblPhone.text = @""; }); } }); } else { cell.lblCustName.text = site.siteName; cell.lblAddr.text = [NSString stringWithFormat:@"%@ %@, %@", site.siteAddressLine1, site.siteCity, site.siteState]; cell.lblPhone.text = [self formatPhoneNum:site.phone]; } </code></pre> <p>As you can see, if you dont already have the UserSite info for a task in <code>_scannedSites</code>, a background thread gets kicked off which gets the UserSite for that task, stores it, and then on the main thread fills in the details.</p> <p>Like I said there is a pretty annoying lag when scrolling... which I hoped to avoid by doing the work in the background.</p> <p>Am I going about this the wrong way?</p> <p>Thanks, any advice is appreciated.</p> <hr> <p><strong>EDIT</strong> I created a relationship in CoreData and I am now using that in <code>cellForRowAtIndexPath</code>. If it does not exist yet, I create it. This is working much better.</p> <pre><code> Site *site = task.site; if(!site) { AppDelegate *ad = [AppDelegate sharedAppDelegate]; NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; temporaryContext.persistentStoreCoordinator = ad.persistentStoreCoordinator; [temporaryContext performBlock:^{ Site *tempContextSite = [task getSiteWithContext:temporaryContext]; [ad.managedObjectContext performBlock:^{ Site *mainManagedObject = (Site *)[ad.managedObjectContext objectWithID:tempContextSite.objectID]; task.site = mainManagedObject; NSError *error; if (![temporaryContext save:&amp;error]) { } [ad.managedObjectContext performBlock:^{ NSError *e = nil; if (![ad.managedObjectContext save:&amp;e]) { } dispatch_async(dispatch_get_main_queue(), ^{ cell.lblCustName.text = mainManagedObject.siteName; cell.lblAddr.text = [NSString stringWithFormat:@"%@ %@, %@", mainManagedObject.siteAddressLine1, mainManagedObject.siteCity, mainManagedObject.siteState]; cell.lblPhone.text = [self formatPhoneNum:mainManagedObject.phone]; }); }]; }]; }]; } else { cell.lblCustName.text = site.siteName; cell.lblAddr.text = [NSString stringWithFormat:@"%@ %@, %@", site.siteAddressLine1, site.siteCity, site.siteState]; cell.lblPhone.text = [self formatPhoneNum:site.phone]; } </code></pre>
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