当我加载要显示给 UICollectionView 的图像时,我会像这样从数组中加载所有图像
- (void)viewDidLoad
{
allImagesArray = [[NSMutableArray alloc] init];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *location=@"Others";
NSString *fPath = [documentsDirectory stringByAppendingPathComponent:location];
NSArray *directoryContent = [[NSFileManager defaultManager] directoryContentsAtPath: fPath];
collectionOthers.delegate =self;
collectionOthers.dataSource=self;
for(NSString *str in directoryContent)
{
NSString *finalFilePath = [fPath stringByAppendingPathComponent:str];
NSData *data = [NSData dataWithContentsOfFile:finalFilePath];
if(data)
{
UIImage *image = [UIImage imageWithData:data];
[allImagesArray addObject:image];
NSLog(@"array:%@",[allImagesArray description]);
image = nil;
}
finalFilePath=nil;
data=nil;
}
paths= nil;
documentsDirectory= nil;
location= nil;
fPath= nil;
directoryContent = nil;
}
这是我的应用程序中最大的问题,因为它使用了太多内存。这是因为图像的数量和大小,这可能会占用内存。我只想在需要时加载图像,并在不再需要时丢弃它们。但是我不知道在哪里以及如何更改我的代码以使其成为那样。我这样做已经三个月左右了,我真的需要帮助。
更新
这是我的特定部分的代码
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *reuseID = @"ReuseID";
OthersCell *mycell = (OthersCell *) [collectionView dequeueReusableCellWithReuseIdentifier:reuseID forIndexPath:indexPath];
UIImageView *imageInCell = (UIImageView*)[mycell viewWithTag:1];
imageInCell.image = [allImagesArray objectAtIndex:indexPath.row];
NSLog(@"a");
return mycell;
}
最佳答案
显然,您应该及时加载图像。永远不要保存一组图像(因为它们占用大量内存),而应该只保存一组文件名。所以我建议您停用 allImagesArray
,而是定义一个名为 filenames
的 NSMutableArray
。然后您可以动态创建 UIImage
对象:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = @"Cell";
OthersCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
UIImageView *imageInCell = (UIImageView*)[cell viewWithTag:1];
imageInCell.image = [UIImage imageWithContentsOfFile:filenames[indexPath.item]];
return cell;
}
当然,这假定您在 viewDidLoad
中填充了 filenames
的 NSMutableArray
:
- (void)viewDidLoad
{
filenames = [[NSMutableArray alloc] init];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *location=@"Others";
NSString *fPath = [documentsDirectory stringByAppendingPathComponent:location];
NSArray *directoryContent = [[NSFileManager defaultManager] directoryContentsAtPath: fPath];
collectionOthers.delegate =self;
collectionOthers.dataSource=self;
for(NSString *str in directoryContent)
{
NSString *finalFilePath = [fPath stringByAppendingPathComponent:str];
[filenames addObject:fileFilePath];
}
}
但是,这有一个问题,因为 imageWithContentsOfFile
(以及首先将其加载到 NSData
然后执行 imageWithData
)是一个如果图像不是很小,则有点慢。在较慢的设备上,这可能会导致快速滚动 Collection View 时出现轻微的卡顿。因此,更好的方法是 (a) 异步加载图像; (b) 使用 NSCache
优化向后滚动时的性能。
所以,首先,定义一个缓存:
@property (nonatomic, strong) NSCache *imageCache;
然后,在 viewDidLoad
中实例化它:
self.imageCache = [[NSCache alloc] init];
self.imageCache.name = @"com.company.app.imageCache";
然后,cellForItemAtIndexPath
可以 (a) 从缓存中设置图像; (b) 如果未找到,则检索图像并适本地异步更新缓存和单元格,例如:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = @"Cell";
OthersCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
UIImageView *imageInCell = (UIImageView*)[cell viewWithTag:1];
NSString *cacheKey = filenames[indexPath.item];
imageInCell.image = [self.imageCache objectForKey:cacheKey];
if (imageInCell.image == nil) {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
UIImage *image = [UIImage imageWithContentsOfFile:filenames[indexPath.item]];
if (image) {
[self.imageCache setObject:image forKey:cacheKey];
dispatch_async(dispatch_get_main_queue(), ^{
OthersCell *updateCell = (id)[collectionView cellForItemAtIndexPath:indexPath];
UIImageView *imageInCell = (UIImageView*)[updateCell viewWithTag:1];
imageInCell.image = image;
});
}
});
}
return cell;
}
而且,显然,如果收到内存警告,请确保清除缓存(在 iOS 7 中,缓存并不总是像过去那样在压力下自动清除自身):
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
[self.imageCache removeAllObjects];
}
关于ios - 仅在需要时加载图像,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/20032408/