In low-memory situations,image data may be purged from a UIImage object to free up memory on the system. This purging behavior affects only the image data stored internally by the UIImage object and not the object itself. When you attempt to draw an image whose data has been purged,the image object automatically reloads the data from its original file. This extra load step,however,may incur a small performance penalty.
事实上,图形数据不会“从UIImage对象中清除,以释放系统上的内存”,但是文档建议.相反,应用程序会收到内存警告,直到它由于内存压力而退出.
编辑：在Xcode项目中使用传统的图像文件引用时,UIImage缓存工作正常.只是转换到资产目录时,内存从未被释放.
我实现了一个UIScrollView与几个UIImageViews滚动浏览一长串图像.当滚动时,下一张图像正在加载并分配给UIImageView的图像属性,从而删除之前已保存的UIImage的强大链接.
由于imageNamed：的缓存机制,我很快就用尽了内存,而应用程序终止了分配大约170 MB的内存.
当然,有很多有趣的解决方案来实现自定义缓存机制,包括覆盖类别中的imageNamed：class方法.通常,使用类方法imageWithContentOfFile：不缓存图像数据,因为即使是由苹果开发商在WWDC 2011提出的建议.
这些解决方案适用于常规的图像文件,尽管您必须获取不像我想要的那样优雅的路径和文件扩展名.
尽管如此,我正在使用Xcode 5中引入的新资产目录,以利用有条件地加载图像的机制,具体取决于设备和高效的图像文件存储.到目前为止,似乎没有直接的方式从资产目录加载图像而不使用imageNamed：,除非我缺少一个明显的解决方案.
你们已经找出了一个UIImage缓存机制与资产目录？
我想在UIImage上实现类似于以下的类别：
static NSCache *_cache = nil;
@implementation UIImage (Caching)
+ (UIImage *)cachedImageNamed:(NSString *)name {
if (!_cache) _cache = [[NSCache alloc] init];
if (![_cache objectForKey:name]) {
UIImage *image = ???; // load image from Asset Catalog without internal caching mechanism
[_cache setObject:image forKey:name];
}
return [_cache objectForKey:name];
}
+ (void)emptyCache {
[_cache removeAllObjects];
}
@end
当然,使用资产目录可以更好地控制UIImage的内部高速缓存以及在低内存条件下清除图像数据的可能性.
感谢您的阅读,期待您的意见！
解决方法
我正在遇到同样的问题(iOS 7.1.1),虽然@Lukas可能是正确的
There is a high probability that the mistake is not inside Apple’s … caching but in your .. code.
所以我写了一个非常简单的测试应用程序(查看下面的完整的源),我仍然看到这个问题.如果你看到有什么问题,请让我知道.我知道它确实取决于图像大小.我只看到iPad Retina的问题.
@interface ViewController ()
@property (nonatomic,strong) UIImageView *imageView;
@property (nonatomic,strong) NSArray *imageArray;
@property (nonatomic) NSUInteger counter;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
self.imageArray = @[@"img1",...,@"img568"];
self.counter = 0;
UIImage *image = [UIImage imageNamed:[self.imageArray objectAtIndex:self.counter]];
self.imageView = [[UIImageView alloc] initWithImage: image];
[self.view addSubview: self.imageView];
[self performSelector:@selector(loadNextImage) withObject:nil afterDelay:1];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
NSLog(@"WARN: %s",__PRETTY_FUNCTION__);
}
- (void)loadNextImage{
self.counter++;
if (self.counter < [self.imageArray count])
{
NSLog(@"INFO: %s - %lu - %@",__PRETTY_FUNCTION__,(unsigned long)self.counter,[self.imageArray objectAtIndex:self.counter]);
UIImage *image = [UIImage imageNamed:[self.imageArray objectAtIndex:self.counter]];
self.imageView.frame = CGRectMake(0,image.size.width,image.size.height);
[self.imageView setImage:image];
[self performSelector:@selector(loadNextImage) withObject:nil afterDelay:0.2];
} else
{
NSLog(@"INFO: %s %@",@"finished");
[self.imageView removeFromSuperview];
}
}
@end
在线实施
我写了一些代码来保持图像资源,但是加载了imageWithData或imageWithContentsOfFile：use xcassets without imageNamed to prevent memory problems?
