好的，所以我从服务器上下载了一堆大图像（5mb），然后将这些碎片拼接在一起并从一个字节数组中渲染出整个图像。但是，我意识到每个图像的数据都没有被释放，因此会导致内存警告和我的应用程序崩溃。我认为，由于我的显式（__bridge_transfer NSData *）转换，ARC将负责释放对象，但它仍然被证明是一个问题。在仪器中，~1mb的称为“CGDataProviderCopyData”的对象会建立起来，并且不会为每个被拼接到整个图像中的文件丢弃。任何想法或任何能引导我朝正确方向前进的人？很有责任。
// Create array to add all files into total image
NSMutableArray *byteArray = [[NSMutableArray alloc] initWithCapacity:(imageHeight * imageWidth)];
// Iterate through each file in files array
for (NSString *file in array)
{
// Set baseURL for individual file path
NSString *baseURL = [NSString stringWithFormat:@"http://xx.225.xxx.xxx%@",[imageInfo objectForKey:@"BaseURL"]];
// Specify imagePath by appending baseURL to file name
NSString *imagePath = [NSString stringWithFormat:@"%@%@", baseURL, file];
// Change NSString --> NSURL --> NSData
NSURL *imageUrl = [NSURL URLWithString:imagePath];
NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];
// Create image from imageData
UIImage *image = [UIImage imageWithData:imageData];
CGImageRef cgimage = image.CGImage;
size_t width = CGImageGetWidth(cgimage);
size_t height = CGImageGetHeight(cgimage);
size_t bpr = CGImageGetBytesPerRow(cgimage);
size_t bpp = CGImageGetBitsPerPixel(cgimage);
size_t bpc = CGImageGetBitsPerComponent(cgimage);
size_t bytes_per_pixel = bpp / bpc;
// Get CGDataProviderRef from cgimage
CGDataProviderRef provider = CGImageGetDataProvider(cgimage);
// This is the object that is not being released
NSData *data = (__bridge_transfer NSData *)CGDataProviderCopyData(provider); //Using (__bridge_transfer NSData *) casts the provider to type NSData and gives ownership to ARC, but still not discarded
const UInt8 *bytes = (Byte *)[data bytes];
// Log which file is currently being iterated through
NSLog(@"---Stitching png file to total image: %@", file);
// Populate byte array with channel data from each pixel
for(size_t row = 0; row < height; row++)
{
for(size_t col = 0; col < width; col++)
{
const UInt8* pixel =
&bytes[row * bpr + col * bytes_per_pixel];
for(unsigned short i = 0; i < 4; i+=4)
{
__unused unsigned short red = pixel[i]; // red channel - unused
unsigned short green = pixel[i+1]; // green channel
unsigned short blue = pixel[i+2]; // blue channel
__unused unsigned short alpha = pixel[i+3]; // alpha channel - unused
// Create dicom intensity value from intensity = [(g *250) + b]
unsigned short dicomInt = ((green * 256) + blue);
//Convert unsigned short intensity value to NSNumber so can store in array as object
NSNumber *DICOMvalue = [NSNumber numberWithInt:dicomInt];
// Add to image array (total image)
[byteArray addObject:DICOMvalue];
}
}
}
data = nil;
}
return byteArray;
通过Xcode运行“Analyze”也没有显示任何明显的泄漏。
答案 0 :(得分：1)
我几乎逐字逐句地接受了这个代码，并做了一些调查。使用CFDataRef / NSData，我能够看到你看到NSDatas没有消失的问题，我能够通过在@autoreleasepool范围内包装使用NSData的代码部分来解决它，像这样：
// Create array to add all files into total image
NSMutableArray *byteArray = [[NSMutableArray alloc] initWithCapacity:(imageHeight * imageWidth)];
// Iterate through each file in files array
for (NSString *file in array)
{
// Set baseURL for individual file path
NSString *baseURL = [NSString stringWithFormat:@"http://xx.225.xxx.xxx%@",[imageInfo objectForKey:@"BaseURL"]];
// Specify imagePath by appending baseURL to file name
NSString *imagePath = [NSString stringWithFormat:@"%@%@", baseURL, file];
// Change NSString --> NSURL --> NSData
NSURL *imageUrl = [NSURL URLWithString:imagePath];
NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];
// Create image from imageData
UIImage *image = [UIImage imageWithData:imageData];
CGImageRef cgimage = image.CGImage;
size_t width = CGImageGetWidth(cgimage);
size_t height = CGImageGetHeight(cgimage);
size_t bpr = CGImageGetBytesPerRow(cgimage);
size_t bpp = CGImageGetBitsPerPixel(cgimage);
size_t bpc = CGImageGetBitsPerComponent(cgimage);
size_t bytes_per_pixel = bpp / bpc;
// Get CGDataProviderRef from cgimage
CGDataProviderRef provider = CGImageGetDataProvider(cgimage);
@autoreleasepool
{
// This is the object that is not being released
NSData *data = (__bridge_transfer NSData *)CGDataProviderCopyData(provider); //Using (__bridge_transfer NSData *) casts the provider to type NSData and gives ownership to ARC, but still not discarded
const UInt8 *bytes = (Byte *)[data bytes];
// Log which file is currently being iterated through
NSLog(@"---Stitching png file to total image: %@", file);
// Populate byte array with channel data from each pixel
for(size_t row = 0; row < height; row++)
{
for(size_t col = 0; col < width; col++)
{
const UInt8* pixel =
&bytes[row * bpr + col * bytes_per_pixel];
for(unsigned short i = 0; i < 4; i+=4)
{
__unused unsigned short red = pixel[i]; // red channel - unused
unsigned short green = pixel[i+1]; // green channel
unsigned short blue = pixel[i+2]; // blue channel
__unused unsigned short alpha = pixel[i+3]; // alpha channel - unused
// Create dicom intensity value from intensity = [(g *250) + b]
unsigned short dicomInt = ((green * 256) + blue);
//Convert unsigned short intensity value to NSNumber so can store in array as object
NSNumber *DICOMvalue = [NSNumber numberWithInt:dicomInt];
// Add to image array (total image)
[byteArray addObject:DICOMvalue];
}
}
}
data = nil;
}
}
return byteArray;
添加@autoreleasepool后，我注释掉你创建NSNumbers的部分并将它们放入数组，我能够在仪器的Allocations模板中看到确实现在，每次循环都会释放CFData对象。
我注释掉你创建NSNumbers并将它们放入数组的部分的原因是，那里有那个代码，你最终会将width * height * 4 NSNumbers添加到byteArray。这意味着即使NSData正确发布，无论如何，您的堆使用量都会增加width * height * 4 * <at least 4 bytes, maybe more>。也许这就是你需要做的事情，但它确实让我更难看到NSDatas发生了什么，因为它们的大小与NSNumbers的数量相形见绌。
希望有所帮助。