无效更新:UICollectionView上的项目数无效

Question

我很难过.这是我的情景.在我的Appdelegate,我正在创造

1. 视图控制器的一个实例,将以模态方式呈现以从用户收集两个数据
2. 一个tableView控制器
3. 我使用tableview控制器作为其根视图
   控制器初始化的导航控制器
4. 一个collectionviewController,请注意我也在这里注册单元格的类.
5. 一个UITabBarController,我将导航控制器添加为第一个视图,将
   集合视图添加为第二个视图.将TabBarCOntorller设置为窗口的根视图.

这是代码:

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:   
(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.evc = [[WTAEntryControllerViewController alloc] init];
WTATableView *tv = [[WTATableView alloc] initWithNibName:@"WTATableView" bundle:nil];
UINavigationController *nav = [[UINavigationController alloc]    
initWithRootViewController:tv];
nav.tabBarItem.title = NSLocalizedString(@"Birthday List", nil);
nav.tabBarItem.image = [UIImage imageNamed:@"birthdaycake"];
WTACollectionViewController *cv = [[WTACollectionViewController alloc] 
initWithCollectionViewLayout:[[UICollectionViewFlowLayout alloc] init]];
[cv.collectionView registerClass:[UICollectionViewCell class] 
forCellWithReuseIdentifier:CellIdentifier];
cv.collectionView.backgroundColor = [UIColor whiteColor];
NSLog(@"cv instance %@", cv);
UITabBarController *tabController = [[UITabBarController alloc] init];
tabController.viewControllers = @[nav, cv];
self.window.rootViewController = tabController;
[self.window makeKeyAndVisible];
return YES
}

tableview有一个导航按钮,用于显示模型视图控制器.模态视图控制器有一个按钮,该按钮从textField和datepicker获取值,并使用UserInfo字典中的值将其发布到默认通知中心.tableView控制器订阅通知,将UserInfo字典放入MutableArray并更新表.这很好.

问题出在CollectionVIew上.collectionVIew接收通知并调用目标方法来处理通知.我试图从通知中获取UserInfo字典并将新单元格添加到collectionView.

但...

当collectionview收到通知时,我收到错误:

'无效更新:第0部分中的项目数无效.更新后的现有部分中包含的项目数(1)必须等于更新前该部分中包含的项目数(1),加上或减去从该部分插入或删除的项目数(插入1个,删除0个),加上或减去移入或移出该部分的项目数(0移入,0移出).

以下是CollectionView的代码:

#import "WTACollectionViewController.h"
#import "UIColor+WTAExtensions.h"
#import "WTAAppDelegate.h"
#import "WTAEntryControllerViewController.h"

@interface WTACollectionViewController () <UICollectionViewDelegateFlowLayout>
@property (strong, nonatomic) NSMutableArray *birthdays;
@end

@implementation WTACollectionViewController

-(id)initWithCollectionViewLayout:(UICollectionViewLayout *)layout{

NSLog(@"Calling init on Collection");
if(!(self = [super initWithCollectionViewLayout:layout])){
    return nil;
}

self.birthdays = [NSMutableArray array];

NSLog(@"Count of Birthdays at init %ld", (long)[self.birthdays count] );
self.title = NSLocalizedString(@"Birthday Grid", nil);
self.tabBarItem.image = [UIImage imageNamed:@"package"];
NSLog(@"cv instance getting notif %@", self);
[[NSNotificationCenter defaultCenter]
 addObserver:self
 selector:@selector(handleNotification:)
 name:@"BirthdayAdded"
 object:nil];
 return self;

}


-(void)handleNotification:(NSNotification *)notification
{
[self.birthdays addObject:[notification userInfo]];
NSLog(@"Count of birthdays when the notification is received: %ld", (long)         
[self.birthdays count]);
[self.collectionView insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:   
(self.birthdays.count -1) inSection:0]]];
}

- (void)viewDidLoad
{
[super viewDidLoad];

NSLog(@"Calling View Did Load on Collection");
}

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {

return 1;

}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:   
(NSInteger)section{

NSLog(@"Count of birthdays in  the number of items in section: %ld", (long)  
[self.birthdays count]);
return [self.birthdays count];
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView    
cellForItemAtIndexPath:(NSIndexPath *)indexPath {

NSLog(@"Calling the cell for index path method");

NSDictionary *dict = [[NSMutableDictionary alloc] init];
dict = self.birthdays[indexPath.item];

UICollectionViewCell *cell = [collectionView   
dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
NSAssert(cell != nil, @"Expected a Cell");

cell.contentView.backgroundColor = [UIColor randomColor];
return cell;

}

#define GAP (1.0f)

-(CGSize)collectionView:(UICollectionView *)collectionView layout:   
(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath   
*)indexPath {


CGFloat edgeLength = self.collectionView.frame.size.width / 4.0f - GAP;
return (CGSize) {.width = edgeLength, .height = edgeLength};
}

-(CGFloat)collectionView:(UICollectionView *)collectionView layout:   
(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:    
(NSInteger)section{

return GAP;
}

-(CGFloat)collectionView:(UICollectionView *)collectionView layout:   
(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:  
(NSInteger)section{

return GAP;
}
@end

我非常感谢能在这里指出任何事情的人.....

Answer 1

这是一个使用insertItemsAtIndexPaths空的错误UICollectionView.这样做:

if (self.birthdays.count == 1) {
    [self.collectionView reloadData];
} else {
    [self.collectionView insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:   (self.birthdays.count -1) inSection:0]]];
}

(不能相信这在iOS8中仍然存在.)

Answer 2

它甚至在iOS 11中也是UICollectionView中的一个错误,但在UITableView中不存在,非常容易重现:假设以下SWIFT代码正在运行:

addItemInDataSource()
collectionView!.insertItems(at: [IndexPath(item: position, section: 0)])

将其更改为:

collectionView!.reloadData()    // <-- This new line will make UICollection crash...

addItemInDataSource()
collectionView!.insertItems(at: [IndexPath(item: position, section: 0)])

它会崩溃......

在某些情况下,UICollectionView将丢失原始项目数,只需在insertItems命令之前添加一个虚拟行就可以避免这种崩溃:

collectionView!.reloadData()

collectionView!.numberOfItems(inSection: 0) //<-- This code is no used, but it will let UICollectionView synchronize number of items, so it will not crash in following code.
addItemInDataSource()
collectionView!.insertItems(at: [IndexPath(item: position, section: 0)])

希望它可以帮助你的情况.

Answer 3

当我在仅包含一个部分的collectionView中插入元素时,我遇到了同样的错误.

我已经完成了蒂莫西的修复,但这还不够.实际上,当我尝试插入新元素时,collectionView已经刷新了它的数据.使用collectionView numberOfItemsInSection可以解决问题.

[self.collectionView performBatchUpdates:^{
        NSMutableArray *arrayWithIndexPaths = [NSMutableArray array];
        for (NSUInteger i = [self.collectionView numberOfItemsInSection:0]; i < self.elements.count ; i++)
        {
            [arrayWithIndexPaths addObject:[NSIndexPath indexPathForRow:i inSection:0]];
        }

        [self.collectionView insertItemsAtIndexPaths:arrayWithIndexPaths];
    } completion:nil];

Answer 4

在我的情况下，numberOfItemsInSection被调用两次self.performBatchUpdates（一次是 BEFORE 编号，一次是 AFTER 编号），因为我试图在视图控制器完成加载之前将某些内容插入到 collectionView 中。

解决方法是guard isViewLoaded else { return }在调用之前添加self.performBatchUpdates。