SDImageCache
使用的内存缓存是NSCache的子类，主要用于在收到APP内存警告时清空缓存
@interface AutoPurgeCache : NSCache
@end
@implementation AutoPurgeCache
- (id)init
{
self = [super init];
if (self) {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(removeAllObjects) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
}
return self;
}
- (void)dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
}
@end
1、定义默认缓存时间
2、定义判断是否是png图片的方式，具体判断如下：ImageDataHasPNGPreffix 是 kPNGSignatureData 就是用kPNGSignatureBytes创建的NSData，通常判断图片类型都只是判断data的第一位，参考NSData+ImageContentType.h,但此处用了8位进行判断是否是png图片，如果前8位都是一样的，则说明是png图片
3、计算图片内存大小
// 默认缓存时间为一周
static const NSInteger kDefaultCacheMaxCacheAge = 60 * 60 * 24 * 7; // 1 week
// PNG signature bytes and data (below)
static unsigned char kPNGSignatureBytes[8] = {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A};
static NSData *kPNGSignatureData = nil;
BOOL ImageDataHasPNGPreffix(NSData *data);
BOOL ImageDataHasPNGPreffix(NSData *data) {
NSUInteger pngSignatureLength = [kPNGSignatureData length];
if ([data length] >= pngSignatureLength) {
if ([[data subdataWithRange:NSMakeRange(0, pngSignatureLength)] isEqualToData:kPNGSignatureData]) {
return YES;
}
}
return NO;
}
// 作为参照判断图片类型，在"NSData+ImageContentType.h"中
+ (NSString *)sd_contentTypeForImageData:(NSData *)data {
uint8_t c;
[data getBytes:&c length:1];
switch (c) {
case 0xFF:
return @"image/jpeg";
case 0x89:
return @"image/png";
case 0x47:
return @"image/gif";
case 0x49:
case 0x4D:
return @"image/tiff";
case 0x52:
// R as RIFF for WEBP
if ([data length] < 12) {
return nil;
}
NSString *testString = [[NSString alloc] initWithData:[data subdataWithRange:NSMakeRange(0, 12)] encoding:NSASCIIStringEncoding];
if ([testString hasPrefix:@"RIFF"] && [testString hasSuffix:@"WEBP"]) {
return @"image/webp";
}
return nil;
}
return nil;
}
// 计算图片内存大小
FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) {
return image.size.height * image.size.width * image.scale * image.scale;
}
主要成员变量有内存缓存已经FileManager
@interface SDImageCache ()
@property (strong, nonatomic) NSCache *memCache;
@property (strong, nonatomic) NSString *diskCachePath;
@property (strong, nonatomic) NSMutableArray *customPaths;
@property (SDDispatchQueueSetterSementics, nonatomic) dispatch_queue_t ioQueue;
@end
@implementation SDImageCache {
NSFileManager *_fileManager;
}
通过命名空间来初始化缓存的名称和磁盘存储的路径，同时添加接收内存警告、应用退出、应用进入后台通知
- (id)initWithNamespace:(NSString *)ns diskCacheDirectory:(NSString *)directory {
if ((self = [super init])) {
NSString *fullNamespace = [@"com.hackemist.SDWebImageCache." stringByAppendingString:ns];
// initialise PNG signature data
kPNGSignatureData = [NSData dataWithBytes:kPNGSignatureBytes length:8];
// Create IO serial queue
_ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
// Init default values
_maxCacheAge = kDefaultCacheMaxCacheAge;
// Init the memory cache
_memCache = [[AutoPurgeCache alloc] init];
_memCache.name = fullNamespace;
// Init the disk cache
if (directory != nil) {
_diskCachePath = [directory stringByAppendingPathComponent:fullNamespace];
} else {
NSString *path = [self makeDiskCachePath:ns];
_diskCachePath = path;
}
// Set decompression to YES
_shouldDecompressImages = YES;
// memory cache enabled
_shouldCacheImagesInMemory = YES;
// Disable iCloud
_shouldDisableiCloud = YES;
dispatch_sync(_ioQueue, ^{
_fileManager = [NSFileManager new];
});
#if TARGET_OS_IOS
// Subscribe to app events
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(clearMemory)
name:UIApplicationDidReceiveMemoryWarningNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(cleanDisk)
name:UIApplicationWillTerminateNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(backgroundCleanDisk)
name:UIApplicationDidEnterBackgroundNotification
object:nil];
#endif
}
return self;
}
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
SDDispatchQueueRelease(_ioQueue);
}
将字符串转换为md5的文件名
- (NSString *)cachedFileNameForKey:(NSString *)key {
const char *str = [key UTF8String];
if (str == NULL) {
str = "";
}
unsigned char r[CC_MD5_DIGEST_LENGTH];
CC_MD5(str, (CC_LONG)strlen(str), r);
NSString *filename = [NSString stringWithFormat:@"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%@",
r[0], r[1], r[2], r[3], r[4], r[5], r[6], r[7], r[8], r[9], r[10],
r[11], r[12], r[13], r[14], r[15], [[key pathExtension] isEqualToString:@""] ? @"" : [NSString stringWithFormat:@".%@", [key pathExtension]]];
return filename;
}
存储图片到内存和磁盘中
1、如果允许存储在内存缓存中，则计算出图片大小，存储在内存中- (void)setObject:(ObjectType)obj forKey:(KeyType)key cost:(NSUInteger)g;
2、将图片存到磁盘上，先判断图片是png还是jpeg
判断png用UIImage判断alpha通道或者NSData判断前8个字节，如果是png图片用UIImagePNGRepresentation(image);获取data，如果是其他图片，用UIImageJPEGRepresentation(image, (CGFloat)1.0);获取data
3、将data存入磁盘
- (void)storeImage:(UIImage *)image recalculateFromImage:(BOOL)recalculate imageData:(NSData *)imageData forKey:(NSString *)key toDisk:(BOOL)toDisk {
if (!image || !key) {
return;
}
// if memory cache is enabled
if (self.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(image);
[self.memCache setObject:image forKey:key cost:cost];
}
if (toDisk) {
dispatch_async(self.ioQueue, ^{
NSData *data = imageData;
if (image && (recalculate || !data)) {
#if TARGET_OS_IPHONE
// We need to determine if the image is a PNG or a JPEG
// PNGs are easier to detect because they have a unique signature (http://www.w3.org/TR/PNG-Structure.html)
// The first eight bytes of a PNG file always contain the following (decimal) values:
// 137 80 78 71 13 10 26 10
// If the imageData is nil (i.e. if trying to save a UIImage directly or the image was transformed on download)
// and the image has an alpha channel, we will consider it PNG to avoid losing the transparency
int alphaInfo = CGImageGetAlphaInfo(image.CGImage);
BOOL hasAlpha = !(alphaInfo == kCGImageAlphaNone ||
alphaInfo == kCGImageAlphaNoneSkipFirst ||
alphaInfo == kCGImageAlphaNoneSkipLast);
BOOL imageIsPng = hasAlpha;
// But if we have an image data, we will look at the preffix
if ([imageData length] >= [kPNGSignatureData length]) {
imageIsPng = ImageDataHasPNGPreffix(imageData);
}
if (imageIsPng) {
data = UIImagePNGRepresentation(image);
}
else {
data = UIImageJPEGRepresentation(image, (CGFloat)1.0);
}
#else
data = [NSBitmapImageRep representationOfImageRepsInArray:image.representations usingType: NSJPEGFileType properties:nil];
#endif
}
[self storeImageDataToDisk:data forKey:key];
});
}
}
NSData存入磁盘的方法
- (void)storeImageDataToDisk:(NSData *)imageData forKey:(NSString *)key {
if (!imageData) {
return;
}
if (![_fileManager fileExistsAtPath:_diskCachePath]) {
[_fileManager createDirectoryAtPath:_diskCachePath withIntermediateDirectories:YES attributes:nil error:NULL];
}
// get cache Path for image key
NSString *cachePathForKey = [self defaultCachePathForKey:key];
// transform to NSUrl
NSURL *fileURL = [NSURL fileURLWithPath:cachePathForKey];
[_fileManager createFileAtPath:cachePathForKey contents:imageData attributes:nil];
// disable iCloud backup
if (self.shouldDisableiCloud) {
[fileURL setResourceValue:[NSNumber numberWithBool:YES] forKey:NSURLIsExcludedFromBackupKey error:nil];
}
}
查找在硬盘上是否存在，先用url转化的key用FileManager查找，如果找不到，把后缀去掉再找一遍
- (BOOL)diskImageExistsWithKey:(NSString *)key {
BOOL exists = NO;
// this is an exception to access the filemanager on another queue than ioQueue, but we are using the shared instance
// from apple docs on NSFileManager: The methods of the shared NSFileManager object can be called from multiple threads safely.
exists = [[NSFileManager defaultManager] fileExistsAtPath:[self defaultCachePathForKey:key]];
// fallback because of https://github.com/rs/SDWebImage/pull/976 that added the extension to the disk file name
// checking the key with and without the extension
if (!exists) {
exists = [[NSFileManager defaultManager] fileExistsAtPath:[[self defaultCachePathForKey:key] stringByDeletingPathExtension]];
}
return exists;
}
- (void)diskImageExistsWithKey:(NSString *)key completion:(SDWebImageCheckCacheCompletionBlock)completionBlock {
dispatch_async(_ioQueue, ^{
BOOL exists = [_fileManager fileExistsAtPath:[self defaultCachePathForKey:key]];
// fallback because of https://github.com/rs/SDWebImage/pull/976 that added the extension to the disk file name
// checking the key with and without the extension
if (!exists) {
exists = [_fileManager fileExistsAtPath:[[self defaultCachePathForKey:key] stringByDeletingPathExtension]];
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock(exists);
});
}
});
}
从硬盘里把图片读取出来
- (UIImage *)diskImageForKey:(NSString *)key {
NSData *data = [self diskImageDataBySearchingAllPathsForKey:key];
if (data) {
// 如果是gif图片，将图片里包含的图片一一取出来[UIImage animatedImageWithImages:images duration:duration];来创建
// 如果是一般图片用[[UIImage alloc] initWithData:data];[UIImage imageWithCGImage:image.CGImage
scale:image.scale
orientation:orientation];创建
// 如果是非gif图片根据屏幕比例伸缩图片
UIImage *image = [UIImage sd_imageWithData:data];
image = [self scaledImageForKey:key image:image];
if (self.shouldDecompressImages) {
image = [UIImage decodedImageWithImage:image];
}
return image;
}
else {
return nil;
}
}
- (NSData *)diskImageDataBySearchingAllPathsForKey:(NSString *)key {
NSString *defaultPath = [self defaultCachePathForKey:key];
NSData *data = [NSData dataWithContentsOfFile:defaultPath];
if (data) {
return data;
}
// fallback because of https://github.com/rs/SDWebImage/pull/976 that added the extension to the disk file name
// checking the key with and without the extension
data = [NSData dataWithContentsOfFile:[defaultPath stringByDeletingPathExtension]];
if (data) {
return data;
}
NSArray *customPaths = [self.customPaths copy];
for (NSString *path in customPaths) {
NSString *filePath = [self cachePathForKey:key inPath:path];
NSData *imageData = [NSData dataWithContentsOfFile:filePath];
if (imageData) {
return imageData;
}
// fallback because of https://github.com/rs/SDWebImage/pull/976 that added the extension to the disk file name
// checking the key with and without the extension
imageData = [NSData dataWithContentsOfFile:[filePath stringByDeletingPathExtension]];
if (imageData) {
return imageData;
}
}
return nil;
}
在内存查找，则直接在cache里用key查找
- (UIImage *)imageFromMemoryCacheForKey:(NSString *)key {
return [self.memCache objectForKey:key];
}
- (UIImage *)imageFromDiskCacheForKey:(NSString *)key {
// First check the in-memory cache...
UIImage *image = [self imageFromMemoryCacheForKey:key];
if (image) {
return image;
}
// Second check the disk cache...
UIImage *diskImage = [self diskImageForKey:key];
if (diskImage && self.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(diskImage);
[self.memCache setObject:diskImage forKey:key cost:cost];
}
return diskImage;
}