uitableview可见细胞不滚动

Question

我有一个tableView，它在每一行中保存正在运行的计时器的输出。它工作正常，直到我尝试在视图的末尾添加一个单元格，然后显示的最后一个单元格与新计时器重叠。我正在使用可重复使用的单元格，我非常怀疑存在内存问题。如果有人有建议，我将不胜感激。我不会发布整个代码，因为它非常混乱（我是一个新开发人员），但这里是与单元格有关的代码部分。

    - (void)tableView: (UITableView*)tableView
  willDisplayCell: (UITableViewCell*)cell
forRowAtIndexPath: (NSIndexPath*)indexPath
{
    cell.backgroundColor = indexPath.row % 2
    ? [UIColor colorWithRed: 0.0 green: 0.3 blue: 1.0 alpha: 0.3]
    : [UIColor whiteColor];
    cell.textLabel.backgroundColor = [UIColor clearColor];
    cell.detailTextLabel.backgroundColor = [UIColor clearColor];
}
// *********************************************************************

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [[[NRCItemStore sharedStore] allItems] count];
}

-(CGFloat) tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{
    return 60.0;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Get a new or recycled cell
    NRCItemCell *cell = [tableView dequeueReusableCellWithIdentifier:@"NRCItemCell" forIndexPath:indexPath];

    self.timerItem.cell = cell;
    [self handleTimer];

    return cell;

    //
//  NRCItemCell.h
//  timeLogger
//
//  Created by Nelson Capes on 10/8/15.
//  Copyright © 2015 Nelson Capes. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@interface NRCItemCell : UITableViewCell
@property (weak, nonatomic) IBOutlet UILabel *timerName;
@property (weak, nonatomic) IBOutlet UILabel *timer;

@property (weak, nonatomic) IBOutlet UIImageView *thumbnailView;

@end

    //
//  NRCItemStore.m
//  timeLogger


#import "NRCItemStore.h"
#import "NRCtimerItem.h"
#import "NRCImageStore.h"

@interface NRCItemStore ()

@property (nonatomic) NSMutableArray *privateItems;

@end

@implementation NRCItemStore

+ (instancetype)sharedStore
{
    static NRCItemStore *sharedStore;

    // Do I need to create a sharedStore?
    if (!sharedStore) {
        sharedStore = [[self alloc] initPrivate];
    }

    return sharedStore;
}

// If a programmer calls [[NRCItemStore alloc] init], let him
// know the error of his ways
- (instancetype)init
{
    @throw [NSException exceptionWithName:@"Singleton"
                                   reason:@"Use +[NRCItemStore sharedStore]"
                                 userInfo:nil];
    return nil;
}

// Here is the real (secret) initializer
- (instancetype)initPrivate
{
    self = [super init];
    if (self) {
        NSString *path = [self itemArchivePath];
        _privateItems = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

        // If the array hadn't been saved previously, create a new empty one
        if (!_privateItems) {
            _privateItems = [[NSMutableArray alloc] init];
        }
    }
    return self;
}

- (NSString *)itemArchivePath
{
    // Make sure that the first argument is NSDocumentDirectory
    // and not NSDocumentationDirectory
    NSArray *documentDirectories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    // Get the one document directory from that list
    NSString *documentDirectory = [documentDirectories firstObject];

    return [documentDirectory stringByAppendingPathComponent:@"items.archive"];
}

- (BOOL)saveChanges
{
    NSString *path = [self itemArchivePath];

    // Returns YES on success
    return [NSKeyedArchiver archiveRootObject:self.privateItems toFile:path];
}

- (NSArray *)allItems
{
    return [self.privateItems copy];
}

- (NRCtimerItem *)createItem
{
    NRCtimerItem *item = [[NRCtimerItem alloc] init];

    [self.privateItems addObject:item];

    return item;
}

- (void)removeItem:(NRCtimerItem *)item
{
        [self.privateItems removeObjectIdenticalTo:item];
}

- (void)moveItemAtIndex:(NSInteger)fromIndex
                toIndex:(NSInteger)toIndex
{
    if (fromIndex == toIndex) {
        return;
    }
    // Get pointer to object being moved so you can re-insert it
    NRCtimerItem *item = self.privateItems[fromIndex];

    // Remove item from array
    [self.privateItems removeObjectAtIndex:fromIndex];

    // Insert item in array at new location
    [self.privateItems insertObject:item atIndex:toIndex];
}

@end