UICollectionView insertItemsAtIndexPaths：抛出异常(UICollectionView insertItemsAtIndexPaths: throws exception)

 UICollectionView：我做错了。 我只是不知道如何。 
 
 我的设置 
 
 我在带有iOS 6.0.1的iPhone 4S上运行它。 
 
 我的目标 
 
 我有一个表视图，其中一个部分专门用于图像： 
 
 当用户点击“添加图像...”单元格时，系统会提示他们从照片库中选择图像或使用相机拍摄新照片。 应用程序的这部分似乎工作正常。 
 
 当用户首次添加图像时，将从第二个表格单元格中删除“无图像”标签，并在其位置添加以编程方式创建的UICollectionView。 那部分似乎也运作良好。 
 
 集合视图应该显示他们添加的图像，它就在我遇到麻烦的地方。 （我知道随着图像数量的增长，我将不得不跳过一些箍来让桌面视图单元扩大。我还没那么远。） 
 
 当我尝试将项目插入到集合视图中时，它会抛出异常。 稍后会详细介绍。 
 
 我的代码 
 
 我有UITableViewController负责表视图也充当集合视图的委托和数据源。 这是相关代码（我省略了我认为与此问题无关的控制器位，包括-viewDidLoad方法中的-viewDidLoad 。我也省略了大部分图像采集代码，因为我认为它不相关） ： 
 
#define ATImageThumbnailMaxDimension 100

@interface ATAddEditActivityViewController ()
{
    UICollectionView* imageDisplayView;
    NSMutableArray* imageViews;
}

@property (weak, nonatomic) IBOutlet UITableViewCell *imageDisplayCell;
@property (weak, nonatomic) IBOutlet UILabel *noImagesLabel;
@end

@implementation ATAddEditActivityViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    UICollectionViewFlowLayout* flowLayout = [[UICollectionViewFlowLayout alloc] init];
    flowLayout.scrollDirection = UICollectionViewScrollDirectionVertical;

    imageDisplayView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, 290, 120) collectionViewLayout:flowLayout];  // The frame rect still needs tweaking
    imageDisplayView.delegate = self;
    imageDisplayView.dataSource = self;
    imageDisplayView.backgroundColor = [UIColor yellowColor];  // Just so I can see the actual extent of the view
    imageDisplayView.opaque = YES;
    [imageDisplayView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];

    imageViews = [NSMutableArray array];
}

#pragma mark - UIImagePickerDelegate
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    /* ...code defining imageToSave omitted... */

    [self addImage:imageToSave toCollectionView:imageDisplayView];


    [self dismissModalViewControllerAnimated:YES];
}

#pragma mark - UICollectionViewDelegate
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return YES;
}

#pragma mark - UICollectionViewDatasource
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell* cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    [[cell  contentView] addSubview:imageViews[indexPath.row]];
    return cell;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return [imageViews count];
}

#pragma mark - UICollectionViewDelegateFlowLayout
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return ((UIImageView*)imageViews[indexPath.item]).bounds.size;
}

#pragma mark - Image Handling
- (void)addImage:(UIImage*)image toCollectionView:(UICollectionView*)cv
{
    if ([imageViews count] == 0)  {
        [self.noImagesLabel removeFromSuperview];
        [self.imageDisplayCell.contentView addSubview:cv];
    }

    UIImageView* imageView = [[UIImageView alloc] initWithImage:image];
    /* ...code that sets the bounds of the image view omitted... */

    [imageViews addObject:imageView];
    [cv insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:[imageViews count]-1 inSection:0]]];
    [cv reloadData];
}

@end
 
 总结： 
 
 
 
 集合视图在-viewDidLoad方法中实例化和配置 
 
 
 接收所选图像的UIImagePickerDelegate方法调用-addImage:toCollectionView 
 
 
 ...创建一个新的图像视图来保存图像并将其添加到数据源数组和集合视图中。 这是产生异常的行。 
 
 
 UICollectionView数据源方法依赖于imageViews数组。 
 
 
 例外 
 
 
 
 由于未捕获的异常'NSInternalInconsistencyException'而终止应用程序，原因：'无效更新：第0节中的项目无效。更新后的现有部分中包含的项目数（1）必须等于该项目中包含的项目数更新前的部分（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量（0移入，0移动）出）。” 
 
 
 如果我正在解析这个权利，这告诉我的是（全新的！）集合视图认为它是用单个项目创建的。 所以，我添加了一个日志到-addImage:toCollectionView来测试这个理论： 
 
NSLog(@"%d", [cv numberOfItemsInSection:0]);
 
 随着那条线，这个例外永远不会被抛出！ 对-numberOfItemsInSection:的调用-numberOfItemsInSection:必须强制集合视图查询其数据源并意识到它没有项目。 或者其他的东西。 我猜想在这里。 但是，好吧，无论如何：集合视图在这一点上仍然没有显示任何项目，所以我仍然做错了什么，我不知道是什么。 
 
 结论是 
 
 
 
 当我尝试将一个项目添加到新建和插入的集合视图时，我得到一个奇怪的例外...除非我在尝试插入之前调用-numberOfItemsInSection: 
 
 
 即使我设法通过阴暗的解决方法超越异常，项目仍然不会显示在集合视图中。 
 
 
 对不起，小问题。 有任何想法吗？ 

UICollectionView: I'm doing it wrong. I just don't know how.
 
My Setup
 
I'm running this on an iPhone 4S with iOS 6.0.1.
 
My Goal
 
I have a table view in which one section is devoted to images: 
 
When the user taps the "Add Image..." cell, they are prompted to either choose an image from their photo library or take a new one with the camera. That part of the app seems to be working fine.
 
When the user first adds an image, the "No Images" label will be removed from the second table cell, and a UICollectionView, created programmatically, is added in its place. That part also seems to be working fine.
 
The collection view is supposed to display the images they have added, and it's here where I'm running into trouble. (I know that I'm going to have to jump through some hoops to get the table view cell to enlarge itself as the number of images grows. I'm not that far yet.)
 
When I attempt to insert an item into the collection view, it throws an exception. More on that later.
 
My Code
 
I've got the UITableViewController in charge of the table view also acting as the collection view's delegate and datasource. Here is the relevant code (I have omitted the bits of the controller that I consider unrelated to this problem, including lines in methods like -viewDidLoad. I've also omitted most of the image acquisition code since I don't think it's relevant):
 
#define ATImageThumbnailMaxDimension 100

@interface ATAddEditActivityViewController ()
{
    UICollectionView* imageDisplayView;
    NSMutableArray* imageViews;
}

@property (weak, nonatomic) IBOutlet UITableViewCell *imageDisplayCell;
@property (weak, nonatomic) IBOutlet UILabel *noImagesLabel;
@end

@implementation ATAddEditActivityViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    UICollectionViewFlowLayout* flowLayout = [[UICollectionViewFlowLayout alloc] init];
    flowLayout.scrollDirection = UICollectionViewScrollDirectionVertical;

    imageDisplayView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, 290, 120) collectionViewLayout:flowLayout];  // The frame rect still needs tweaking
    imageDisplayView.delegate = self;
    imageDisplayView.dataSource = self;
    imageDisplayView.backgroundColor = [UIColor yellowColor];  // Just so I can see the actual extent of the view
    imageDisplayView.opaque = YES;
    [imageDisplayView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];

    imageViews = [NSMutableArray array];
}

#pragma mark - UIImagePickerDelegate
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    /* ...code defining imageToSave omitted... */

    [self addImage:imageToSave toCollectionView:imageDisplayView];


    [self dismissModalViewControllerAnimated:YES];
}

#pragma mark - UICollectionViewDelegate
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return YES;
}

#pragma mark - UICollectionViewDatasource
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell* cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    [[cell  contentView] addSubview:imageViews[indexPath.row]];
    return cell;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return [imageViews count];
}

#pragma mark - UICollectionViewDelegateFlowLayout
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return ((UIImageView*)imageViews[indexPath.item]).bounds.size;
}

#pragma mark - Image Handling
- (void)addImage:(UIImage*)image toCollectionView:(UICollectionView*)cv
{
    if ([imageViews count] == 0)  {
        [self.noImagesLabel removeFromSuperview];
        [self.imageDisplayCell.contentView addSubview:cv];
    }

    UIImageView* imageView = [[UIImageView alloc] initWithImage:image];
    /* ...code that sets the bounds of the image view omitted... */

    [imageViews addObject:imageView];
    [cv insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:[imageViews count]-1 inSection:0]]];
    [cv reloadData];
}

@end
 
To summarize:
 
 
 
The collection view is instantiated and configured in the -viewDidLoad method
 
 
The UIImagePickerDelegate method that receives the chosen image calls -addImage:toCollectionView
 
 
...which creates a new image view to hold the image and adds it to the datasource array and collection view. This is the line that produces the exception.
 
 
The UICollectionView datasource methods rely on the imageViews array.
 
 
The Exception
 
 
 
Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '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).'
 
 
If I'm parsing this right, what this is telling me is that the (brand new!) collection view thinks it was created with a single item. So, I added a log to -addImage:toCollectionView to test this theory:
 
NSLog(@"%d", [cv numberOfItemsInSection:0]);
 
With that line in there, the exception never gets thrown! The call to -numberOfItemsInSection: must force the collection view to consult its datasource and realize that it has no items. Or something. I'm conjecturing here. But, well, whatever: the collection view still doesn't display any items at this point, so I'm still doing something wrong and I don't know what.
 
In Conclusion
 
 
 
I get an odd exception when I attempt to add an item to a newly-minted-and-inserted collection view...except when I call -numberOfItemsInSection: before attempting insertion.
 
 
Even if I manage to get past the exception with a shady workaround, the items still do not show up in the collection view.
 
 
Sorry for the novel of a question. Any ideas?

原文：https://stackoverflow.com/questions/13392413