UIImage dealloc 永远不会被调用

Question

我试图弄清楚为什么我的应用程序使用大量内存，然后在多次内存警告后崩溃。 Instrument VM Tracker 显示它使用 ~30Mb 作为脏内存。分配显示 10-15 Mb 不是那么多。 一旦应用程序处理显示大量图像（缩略图），我认为图像是我应该看的。 我不使用标准的 UIImage imageNamed 方法，而是使用 imageWithData 并进行缓存。当系统发送内存警告时，我会清理缓存存储。为了确保我创建的图像在不再需要时被销毁，我将 UIImage 子类化并覆盖了 imageWithData、release 和 dealloc 方法。我可以看到 imageWithData 被调用，但 release 和 dealloc 从未被调用。 我就是这样做的：

BaseUIimage.h

@interface BaseUIimage : UIImage

@end

BaseUIimage.m

#import "BaseUIimage.h"

@implementation BaseUIimage

+ (id)imageWithData:(NSData *)data {
    NSLog(@"UIImage imageWithData");
    return [UIImage imageWithData:data];
}

- (id)retain {
    NSLog(@"UIImage retain: %d", [self retainCount]);
    return [super retain];
}

- (oneway void)release {
    NSLog(@"UIImage release: %d", [self retainCount]);
    [super release];
}

- (id)autorelease {
    NSLog(@"UIImage autorelease: %d", [self retainCount]);
    return [super autorelease];
}

- (void)dealloc {
    NSLog(@"UIImage deallocated");
    [super dealloc];
}

@end

我的缓存代码：

.h

#import "BaseUIimage.h"

@interface UIImageCached : BaseUIimage

// CACHE
+ (NSMutableDictionary*) cache;
+ (void) cleanCache;
+ (UIImageCached *)imageNamed:(NSString *)imageName;
+ (UIImageCached *)retinaImageNamed:(NSString *)imageName;
+ (UIImageCached *)imageFromPath:(NSString *)imagePath;

.m

#import "UIImageCached.h"

@implementation UIImageCached

static NSMutableDictionary *data;

+ (NSMutableDictionary*) cache {
    if (data == nil)
        data = [[NSMutableDictionary alloc] initWithCapacity:150];
    return data;
}

+ (void) cleanCache {
    NSLog(@"Cache cleaned images: %d", data.count);

    for (BaseUIimage *image in data) {
        NSLog(@"image rc: %d", [image retainCount]); // always prints rc = 1
    }

    [data removeAllObjects];
}

+ (UIImageCached *)imageFromPath:(NSString *)imagePath {
    UIImageCached *image = (UIImageCached*)[self.cache objectForKey:imagePath];
    if (image == nil) {
        NSData *imageData = [[NSData alloc] initWithContentsOfFile:imagePath options:NSDataReadingMappedIfSafe error:nil];
        image = (UIImageCached*)[UIImageCached imageWithData:imageData];
        [imageData release];

        if (image) {
            [self.cache setObject:image forKey:imagePath];
            //NSLog(@"new cached image: #%d", self.cache.count);
        } else {
            //NSLog(@"can't cache image: #%d", self.cache.count);
        }
    }

    return image;
}

+ (UIImageCached *)imageNamed:(NSString *)imageName {
    NSString *extension = [imageName pathExtension];
    NSString *fileName = [imageName stringByDeletingPathExtension];
    NSString *fileLocation = [[NSBundle mainBundle] pathForResource:fileName ofType:extension];
    return [self imageFromPath:fileLocation];
}

+ (UIImageCached *)retinaImageNamed:(NSString *)imageName {
    UIImageCached *image = (UIImageCached*)[self.cache objectForKey:imageName];
    if (image == nil) {
        NSString *extension = [imageName pathExtension];
        NSString *fileName = [imageName stringByDeletingPathExtension];

        float s = 1.0;

        // retina filename support
        if(!isIPAD && [[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
            s = [[UIScreen mainScreen] scale];
            if (s > 1)
                fileName = NSTR2(@"%@%@", fileName, @"@2x");            
        }

        NSString *fileLocation = [[NSBundle mainBundle] pathForResource:fileName ofType:extension];

        NSData *imgData = [[NSData alloc] initWithContentsOfFile:fileLocation options:NSDataReadingMappedIfSafe error:nil];

        BaseUIimage *tmpImage = [[BaseUIimage alloc] initWithData:imgData];

        [imgData release];

        image = (UIImageCached*)[UIImageCached imageWithCGImage:tmpImage.CGImage 
                                                    scale:s 
                                              orientation:UIImageOrientationUp];        

        [tmpImage release];

        if (image) {
            [self.cache setObject:image forKey:imageName];
            //NSLog(@"-- CACHE: new cached image: #%d", self.cache.count);          
        } else {
            NSLog(@"-- CACHE: can't cache image: %@", fileLocation);
        }
    } else {
        //NSLog(@"-- CACHE: read cached image");
    }
    return image;
}

@end

为什么从不调用 release 和 dealloc？这是否意味着我创建的 UIImage 实例没有被释放，这就是虚拟内存增长的原因？

Answer 1

Dave Wood 几乎是对的（他的实现仍然会创建一个 UIImage）。问题是

[UIImage imageWithData:data];

将创建一个 UIImage 而不是您期望它创建的子类。要对此进行测试，请尝试以下 imageWithData 实现：

+ (id)imageWithData:(NSData *)data {
    NSLog(@"UIImage imageWithData");
    UIImage *im = [UIImage imageWithData:data];
    NSLog(@"%@",[im class]);
    return im;
}

NSLog 会输出 UIImage。不是你需要的。我建议以下实现：

+ (id)imageWithData:(NSData *)data {
    NSLog(@"UIImage imageWithData");
    BaseUIimage *im = [[BaseUIimage alloc] initWithData:data];
    return [im autorelease];
}

这将创建 BaseUIimage 类的图像，从而表现出您的预期。干杯。

Answer 2

您创建了错误的子类。在这里的代码中：

@implementation BaseUIimage

+ (id)imageWithData:(NSData *)data {
    NSLog(@"UIImage imageWithData");
    return [UIImage imageWithData:data];
}

...

你没有得到 BaseUIimage 的实例，你得到的是一个常规的 UIImage，这意味着你覆盖的 release/dealloc 等不会被调用，因为它们不是 UIImage 类的一部分。

您需要将该函数更改为：

@implementation BaseUIimage

+ (id)imageWithData:(NSData *)data {
    NSLog(@"UIImage imageWithData");
    return [super imageWithData:data];
}

...

这将返回您的 BaseUIimage 类的实例。现在您将能够看到被覆盖的方法被调用了。