Question

我有一个名为UICollectionViewCell的{{1}}子类，其中包含一个名为AlbumCVC的{{1}} --- IBOutlet。我在以下方法中为每个单元格设置UIImageView的值：

cellView

其中cellView是- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{ UICollectionViewCell *cell; cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"albumPhotoCell" forIndexPath:indexPath]; cell.backgroundColor = [UIColor blueColor]; if ([cell isKindOfClass:[AlbumCVC class]]){ AlbumCVC *albumCVC = (AlbumCVC *)cell; ALAsset *thisImage = [self.albumPhotos objectAtIndex:indexPath.item]; albumCVC.imageView.frame = albumCVC.contentView.frame; albumCVC.contentView.contentMode = UIViewContentModeScaleAspectFit; albumCVC.imageView.image = [UIImage imageWithCGImage:[thisImage aspectRatioThumbnail]]; } } return cell; }的NSMutableArray。我确定该属性设置正确，因为我在记录albumPhotos时得到了明智的结果。当我设置背景颜色时，单元格的大小也正确，因为框架是可见的。但由于某种原因，ALAsset将无法显示。我需要在albumCVC.cellImage.image.bounds.size内进行另一个方法调用才能显示图像吗？

更新：根据一个非常聪明的朋友的建议，我尝试将cellImage移出单元格，将其放在主视图的其他位置，一切都很可爱。问题似乎与collectionView:cellForItemAtIndexPath:的框架/边界有关。我认为我需要进行一个方法调用，以便在调用UIImageView之后，单元格的子视图扩展为适合新调整大小的单元格。现在的问题是UIImageView是一个只读属性，所以我无法直接调整它。

更新2：在另一条建议中，我查看了单元格collectionView:layout:sizeForItemAtIndexPath:和UIImageView.image.size的边框和边界，发现它们没有匹配。添加了另一个方法调用以使它们相等，甚至将contentView更改为cellImage以尝试让单元格正确呈现缩略图。不幸的是，我仍然在巨大的细胞内获得微小的缩略图。知道为什么吗？上面和下面的更新代码。

为了完整起见，这是整个类的实现：

contentMode

更新3：我无法确定最初的问题是什么，但我知道它现在适用于以下UIViewContentModeScaleAspectFit实施：

#import "AlbumViewController.h"
#import "AlbumCVC.h"
#import <AssetsLibrary/AssetsLibrary.h>

@interface AlbumViewController ()
@end

@implementation AlbumViewController


#pragma constants

const int IPHONE_WIDTH = 320;

#pragma delegate methods

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

    // Get the count of photos in album at index albumIndex in the PhotoHandler
    NSInteger numCells = [self.group numberOfAssets];
    return numCells;

}

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

    UICollectionViewCell *cell;

    cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"albumPhotoCell" forIndexPath:indexPath];
    cell.backgroundColor = [UIColor blueColor];
    if ([cell isKindOfClass:[AlbumCVC class]]){
        AlbumCVC *albumCVC = (AlbumCVC *)cell;
        ALAsset *thisImage = [self.albumPhotos objectAtIndex:indexPath.item];
        }

        albumCVC.imageView.frame = albumCVC.contentView.frame;
        albumCVC.contentView.contentMode = UIViewContentModeScaleAspectFit;
        albumCVC.imageView.image = [UIImage imageWithCGImage:[thisImage aspectRatioThumbnail]];

    }
    return cell;
}

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


    //Copy a pointer to an asset from the album
    ALAsset *thisImage = [self.albumPhotos objectAtIndex:indexPath.item]; //Zen - are you sure thisImage represents a valid image?

    //Copy that asset's size and create a new size struct
    CGSize thisSize = thisImage.defaultRepresentation.dimensions;
    CGSize returnSize;

    // force all previews to be full width
    returnSize.width = IPHONE_WIDTH;
    returnSize.height = IPHONE_WIDTH * thisSize.height / thisSize.width;

    return returnSize;
}


#pragma lifecycle methods

- (void)viewWillAppear:(BOOL)animated{
    [self.albumPhotos removeAllObjects];

//"handler" is a class that manages calls to the ALAssetLibrary. self.albumIndex is an integer that gets set on segue. As far as I can tell, everything in the below method is working fine --- cells are sized properly.

    self.group = self.albumDelegate.handler.groups[self.albumIndex];
    [self.group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
        if (result) {
            NSLog(@"Just added an object to albumPhotos.");
            [self.albumPhotos addObject:result];
            NSLog(@"The item in albumPhotos is class %@", [self.albumPhotos[0] class]);
        }
    }]; 

}


#pragma instantiation

- (ALAssetsGroup *)group{
    if (!_group) {
        _group = [[ALAssetsGroup alloc]init];
    }
    return _group;
}

- (NSMutableArray *)albumPhotos{
    if (!_albumPhotos) {
        _albumPhotos = [[NSMutableArray alloc]init];
    }
    return _albumPhotos;
}

@end

任何地方都没有框架或边界，一切正常。也许这是cellForItem和- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{ UICollectionViewCell *cell; cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"albumPhotoCell" forIndexPath:indexPath]; if ([cell isKindOfClass:[AlbumCVC class]]) { AlbumCVC *albumCVC = (AlbumCVC *)cell; albumCVC.albumImageView.image = [[UIImage alloc] initWithCGImage:[self.albumAssets[[self reverseAlbumIndexForIndex:indexPath.item]] thumbnail]]; } cell.alpha = [self alphaForSelected:self.selectedItems[@(indexPath.item)]]; return cell; }之间的区别？

Answer 1

我遇到了类似的问题，并通过将UICollectionViewCell框架属性设置为与UIImageView的框架相同来解决它。我不是100％确定这是你的问题，我只是在代码中构建集合（没有故事板）

包含UIImageView出口的UICollectionViewCell子类不显示图像

1 个答案: