UITableView cellForRowAtIndexPath为每一行调用多次
如果我有一个UITableView中有4行，那么当我导航到该视图时不应调用cellForRowAtIndexPath方法4次？ 我发现它被多次调用，例如，如果有4行，当我向下钻入UITable视图时调用8次，然后再导航回到同一个UITableView。
我只是误解这种方法如何工作？ 我认为应该为显示的每一行调用一次（因为表视图的内容很容易适合我的iPad屏幕，所以不涉及滚动）。
我应该注意到，UITableView包含在iPad的UISplitViewController的MasterViewController中。
编辑：我得到的真正的问题是在应用下面的代码的方式不一致：
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; } 当我第一次“钻取”到我的导航堆栈的特定级别时，事情就像他们应该的那样工作。 但后来，如果我向上或向下导航，那么我发现不同的行得到不正确的处理，即他们应该被启用时最终禁用。 这导致我把一个断点和一些日志代码试图找出发生了什么事情。 我发现上面的代码比被调用的次数要多 – 而且我logging的cell.textLabel.text值没有任何意义 – 同一行的值被多次logging – 其他行不是被logging在一切。
编辑：提供一些代码请求：
- (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"]; } } }
该方法在单元出现时被调用，所以每当一个单元出现时，该方法被调用。 另外，这些单元被重新使用。 所以即使某个特定单元格的方法被调用了一次，也可能在这个单元格消失的时候再次调用，然后再次出现。
很有可能你是从其他方法调用：
UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath将调用cellForRowAtIndexPath两次。