我有一个UICollectionViewCell名为的子类AlbumCVC，其中包含一个IBOutlet--- 一个UIImageView被调用的cellView. 我cellView在以下方法中为每个单元格设置值：
- (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ALAssets 的 NSMutableArray。我确信该属性设置正确，因为我在登录albumCVC.cellImage.image.bounds.size. 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，cellImage不会显示。collectionView:cellForItemAtIndexPath:为了显示图像，我需要在内部进行其他方法调用吗？
更新：在一位非常聪明的朋友的建议下，我尝试将其UIImageView移出单元格，将其放在主视图的其他位置，一切都很顺利。该问题似乎与UIImageView. 我认为我需要进行一个方法调用，以便单元格的子视图在调用collectionView:layout:sizeForItemAtIndexPath:. 现在的问题是这UIImageView.image.size是一个只读属性，所以我不能直接调整它的大小。
更新 2：在另一条建议中，我查看了单元格的框架和边界，contentView发现cellImage它们不匹配。添加了另一个方法调用以使它们相等，甚至更改contentMode为UIViewContentModeScaleAspectFit以尝试使单元格正确呈现缩略图。不幸的是，我仍然在巨大的单元格中看到微小的缩略图。知道为什么吗？更新了上面和下面的代码。
为了完整起见，这是整个类的实现：
#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：我无法确定最初的问题是什么，但我知道它现在适用于以下cellForItem实现：
- (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;
}
任何地方都没有框架或边界，一切正常。[[UIImage alloc]initWithCGImage]也许这是和之间的区别[UIImage imageWithCGImage]？