无效更新:UICollectionView 上的项目数无效

问题描述

我对此感到困惑.这是我的场景.在我的 Appdelegate 中，我正在创建

I am stumped on this. Here is my scenario. In my Appdelegate, I am creating

1. 一个视图控制器的实例，它将以模态方式呈现以从用户那里收集两条数据
2. 一个 tableView 控制器
3. 我以 tableview 控制器作为其根视图初始化的导航控制器
   控制器
4. 一个collectionviewController，注意我在这里也注册了单元格的类.
5. 我将导航控制器添加到的 UITabBarController 作为第一个视图和
   collectionview 作为第二个视图.TabBarCONtorller 被设置为窗口的根视图.

代码如下:

 - (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 有一个显示模型视图控制器的导航栏按钮.模态视图控制器有一个按钮，该按钮从 textField 和 datepicker 中获取值，并将其与 UserInfo 字典中的值一起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.这很好用.

The tableview has a navbar button that presents the model view controller. The modal view controller has a button that takes the values from a textField and a datepicker and posts that to the default notification center with the values in the UserInfo dictionary. The tableView contorller subscribes to the notification, puts the UserInfo dictionary in a MutableArray and updates the table. That works fine.

问题出在 CollectionVIew 上.collectionVIew 接收通知并调用目标方法来处理通知.我正在尝试从通知中获取 UserInfo 字典并向 collectionView 添加一个新单元格.

The problem is with the CollectionVIew. The collectionVIew receives the notification and calls a target method to handle the notification. I am trying to take the UserInfo dictionary from the notification and add a new cell to the collectionView.

但是……

当 collectionview 收到通知时，我收到错误消息:

When the collectionview receives the notification I get the error:

'无效更新:第0节中的项目数无效.更新后现有节中包含的项目数(1)必须等于更新前该节中包含的项目数(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).'

'Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (1) must be equal to the number of items contained in that section before the update (1), plus or minus the number of items inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out).'

这是 CollectionView 的代码:

Here is the code for the CollectionView:

#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

我非常感谢任何可以在这里指出任何事情的人.....

I would so much appreciate anyone who can point anything out here.....

推荐答案

这是在空 UICollectionView 上使用 insertItemsAtIndexPaths 的错误.只需这样做:

It's a bug with using insertItemsAtIndexPaths on an empty UICollectionView. Just do this:

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

(不敢相信这在 iOS8 中仍然被破坏.)

(Can't believe this is still broken in iOS8.)

这篇关于无效更新:UICollectionView 上的项目数无效的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！