UICollectionViewCell子類包含UIImageView插座不顯示圖像

Question

我有一個UICollectionViewCell子類AlbumCVC包含單個IBOutlet --- UIImageView稱爲cellView。我以下方法內的每個小區設置的cellView值：

- (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; 
} 

其中albumPhotos是ALAsset秒的的NSMutableArray。我確信該物業正在設置正確，因爲當我登錄albumCVC.cellImage.image.bounds.size時，我得到了明智的結果。單元格大小也適當，因爲當我設置背景顏色時，框架可見。但由於某些原因，cellImage將不會顯示。我需要在collectionView:cellForItemAtIndexPath:內部進行另一種方法調用，才能顯示圖像？

更新：在一個非常聰明的朋友的建議下，我嘗試移動UIImageView出細胞，把它在其他地方的主要觀點，和一切工作可愛。這個問題似乎與UIImageView的框架/範圍有關。我認爲我需要做一個方法調用，以便在調用collectionView:layout:sizeForItemAtIndexPath:之後，單元格的子視圖擴展爲適合新調整大小的單元格。現在的問題是，UIImageView.image.size是隻讀屬性，所以我無法直接調整它的大小。

更新2：在另一個忠告我看着框架和電池的contentView和cellImage的界限，發現他們不匹配起來。添加了另一個方法調用以使它們相等，甚至將contentMode更改爲UIViewContentModeScaleAspectFit以試圖讓單元格正確地呈現縮略圖。不幸的是，我仍然在巨大的單元格內獲得小縮略圖。任何想法爲什麼？上面和下面更新了代碼。

爲了完整起見，這裏的整個類實現：

#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 

更新3：我不能確定的問題是什麼開始，但我知道它現在用下面的工作cellForItem實現：

- (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; 
} 

有沒有用框架或界限胡鬧的任何地方，一切都只是工作。也許這是[[UIImage alloc]initWithCGImage]和[UIImage imageWithCGImage]之間的區別？

Answer 1

我有過類似的問題，並通過設置UICollectionViewCell框架屬性與UIImageView的框架相同來解決它。我不是100％確定這是你的問題，我只是在代碼中構建集合（沒有Storyboard）