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UITableView cellForRowAtIndexPath called more than once for each row

If I have a UITableView that has 4 rows, then you should not call the cellForRowAtIndexPath method 4 times when I switch to this view? I find it called several times, for example. if there are 4 rows, this is called 8 times when I go to the UITable view, and then 12 times when I go back to the same UITableView.

I just don’t understand how this method works? I thought it needed to be called once for each row displayed (no scrolling, since the contents of the table view fit easily on my iPad screen).

I should probably point out that the UITableView is contained in the MasterViewController of the UISplitViewController on the iPad.

EDIT: The real problem I'm getting is inconsistency in how the following code applies:

if (selectedNavItem.folder.isAssignedToUser != [NSNumber numberWithInt:1]) { NSLog(@"%@", cell.textLabel.text); cell.selectionStyle = UITableViewCellSelectionStyleNone; cell.userInteractionEnabled = NO; cell.textLabel.enabled = NO; cell.detailTextLabel.text = @"Access not granted"; cell.detailTextLabel.enabled = NO; }

When I first “turn around” to a certain level of my navigation stack, everything works as it should. But later, if I move back or down, I find that various lines are not processed correctly, that is, they are ultimately disabled when they should be included. This made me set a breakpoint and some registration code to try to figure out what was going on. I found that the above code was called more times than there were lines - and the value of cell.textLabel.text that I registered did not make sense - the value for the same line was registered several times - and the other lines were not registered at all .

EDIT: providing code on request:

  - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"FolderCell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; [self configureCell:cell atIndexPath:indexPath]; return cell; } - (NSFetchedResultsController *)fetchedResultsController { if (__fetchedResultsController != nil) { return __fetchedResultsController; } // Set up the fetched results controller. // Create the fetch request for the entity. NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; // Edit the entity name as appropriate. NSEntityDescription *entity = [NSEntityDescription entityForName:@"NavItem" inManagedObjectContext:self.managedObjectContext]; [fetchRequest setEntity:entity]; // Set the batch size to a suitable number. [fetchRequest setFetchBatchSize:20]; // Edit the sort keys as appropriate. NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"sortOrder" ascending:YES]; NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)]; NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor1, sortDescriptor2, nil]; [fetchRequest setSortDescriptors:sortDescriptors]; // Edit the section name key path and cache name if appropriate. // nil for section name key path means "no sections". NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self. managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController; NSError *error = nil; if (![self.fetchedResultsController performFetch:&error]) { /* Replace this implementation with code to handle the error appropriately. abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. */ NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } return __fetchedResultsController; } - (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath { NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath]; NavItem *selectedNavItem = (NavItem *)managedObject; cell.textLabel.text = [[managedObject valueForKey:@"name"] description]; cell.detailTextLabel.text = @""; if (selectedNavItem.folder != nil) { cell.imageView.image = [UIImage imageNamed:@"Folder.png"]; //NSLog(@"%@", selectedNavItem.folder.isAssignedToUser); if (selectedNavItem.folder.isAssignedToUser != [NSNumber numberWithInt:1]) { NSLog(@"%@", cell.textLabel.text); cell.selectionStyle = UITableViewCellSelectionStyleNone; cell.userInteractionEnabled = NO; cell.textLabel.enabled = NO; cell.detailTextLabel.text = @"Access not granted"; cell.detailTextLabel.enabled = NO; } } else if (selectedNavItem.document != nil) { cell.detailTextLabel.text = [[selectedNavItem.document valueForKey:@"itemDescription"] description]; if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"pdf"]) { cell.imageView.image = [UIImage imageNamed:@"pdf.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"doc"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"docx"]) { cell.imageView.image = [UIImage imageNamed:@"Word-32x32.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"xls"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"xlsx"]) { cell.imageView.image = [UIImage imageNamed:@"Excel-32x32.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"ppt"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"pps"]) { cell.imageView.image = [UIImage imageNamed:@"Powerpoint-32x32.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"mp3"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"wav"]) { cell.imageView.image = [UIImage imageNamed:@"65-note.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"mp4"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"mov"]) { cell.imageView.image = [UIImage imageNamed:@"46-movie-2.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"ibooks"]) { cell.imageView.image = [UIImage imageNamed:@"ibooks-icon.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"png"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"bmp"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"jpg"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"jpeg"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"tif"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"tiff"] || [[selectedNavItem.document.fileName pathExtension] isEqualToString:@"gif"]) { cell.imageView.image = [UIImage imageNamed:@"41-picture-frame.png"]; } else { cell.imageView.image = [UIImage imageNamed:@"179-notepad.png"]; } } else if (selectedNavItem.attachment != nil) { cell.detailTextLabel.text = [[selectedNavItem.attachment valueForKey:@"itemDescription"] description]; if ([[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"pdf"]) { cell.imageView.image = [UIImage imageNamed:@"pdf.png"]; } else if ([[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"doc"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"docx"]) { cell.imageView.image = [UIImage imageNamed:@"Word-32x32.png"]; } else if ([[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"xls"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"xlsx"]) { cell.imageView.image = [UIImage imageNamed:@"Excel-32x32.png"]; } else if ([[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"ppt"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"pps"]) { cell.imageView.image = [UIImage imageNamed:@"Powerpoint-32x32.png"]; } else if ([[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"mp3"]) { cell.imageView.image = [UIImage imageNamed:@"65-note.png"]; } else if ([[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"mp4"]) { cell.imageView.image = [UIImage imageNamed:@"46-movie-2.png"]; } else if ([[selectedNavItem.document.fileName pathExtension] isEqualToString:@"ibooks"]) { cell.imageView.image = [UIImage imageNamed:@"ibooks-icon.png"]; } else if ([[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"png"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"bmp"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"jpg"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"jpeg"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"tif"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"tiff"] || [[selectedNavItem.attachment.fileName pathExtension] isEqualToString:@"gif"]) { cell.imageView.image = [UIImage imageNamed:@"41-picture-frame.png"]; } else { cell.imageView.image = [UIImage imageNamed:@"179-notepad.png"]; } } }
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3 answers

A method is called when a cell appears, so whenever a cell appears, a method is called. In addition, the cells are reused. Therefore, even if a method for a particular cell is called once, it may be called at another time when that cell disappears and then reappears.

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It is very likely that you are calling other methods:

 UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];

self.tableView externally - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath will call cellForRowAtIndexPath twice.

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swift

 DispatchQueue.main.async { //Add selection in main queue }

This will solve the problem.

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Source: https://habr.com/ru/post/915484/

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