SDImageCache 是一个单例类，完成了对图片的内存缓存、异步磁盘缓存、图片缓存查询等功能，将下载过的图片缓存到内存和本地磁盘，当再次请求相同图片时直接从缓存中提取图片，从而大大提高了加载速度。
SDImageCache.h
#import <Foundation/Foundation.h>
#import "SDWebImageCompat.h"
#import "SDImageCacheConfig.h"
typedef NS_ENUM(NSInteger, SDImageCacheType) {
/**
* The image wasn't available the SDWebImage caches, but was downloaded from the web.
*/
SDImageCacheTypeNone, //不使用缓存
/**
* The image was obtained from the disk cache.
*/
SDImageCacheTypeDisk, //磁盘缓存
/**
* The image was obtained from the memory cache.
*/
SDImageCacheTypeMemory //内存缓存
};
typedef void(^SDCacheQueryCompletedBlock)(UIImage * _Nullable image, NSData * _Nullable data, SDImageCacheType cacheType);
typedef void(^SDWebImageCheckCacheCompletionBlock)(BOOL isInCache);
typedef void(^SDWebImageCalculateSizeBlock)(NSUInteger fileCount, NSUInteger totalSize);
/**
* SDImageCache maintains a memory cache and an optional disk cache. Disk cache write operations are performed
* asynchronous so it doesn’t add unnecessary latency to the UI.
*/
//SDImageCache维护了一个内存缓存和一个可选择的磁盘缓存,磁盘缓存是异步的所以不会堵塞UI
@interface SDImageCache : NSObject
#pragma mark - Properties
/**
* Cache Config object - storing all kind of settings
*/
//缓存配置对象 保存所有的设置
@property (nonatomic, nonnull, readonly) SDImageCacheConfig *config;
/**
* The maximum "total cost" of the in-memory image cache. The cost function is the number of pixels held in memory.
*/
//内存缓存中最大的cost,cost是在内存中存储的像素数.
@property (assign, nonatomic) NSUInteger maxMemoryCost;
/**
* The maximum number of objects the cache should hold.
*/
//缓存最大数量
@property (assign, nonatomic) NSUInteger maxMemoryCountLimit;
#pragma mark - Singleton and initialization
/**
* Returns global shared cache instance
*
* @return SDImageCache global instance
*/
//ImageCache单例
+ (nonnull instancetype)sharedImageCache;
/**
* Init a new cache store with a specific namespace
*
* @param ns The namespace to use for this cache store
*/
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns;
/**
* Init a new cache store with a specific namespace and directory
*
* @param ns The namespace to use for this cache store
* @param directory Directory to cache disk images in
*/
//用命名空间和目录初始化一个新的缓存存储
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns
diskCacheDirectory:(nonnull NSString *)directory NS_DESIGNATED_INITIALIZER;
#pragma mark - Cache paths
//读取磁盘的缓存路径
- (nullable NSString *)makeDiskCachePath:(nonnull NSString*)fullNamespace;
/**
* Add a read-only cache path to search for images pre-cached by SDImageCache
* Useful if you want to bundle pre-loaded images with your app
*
* @param path The path to use for this read-only cache path
*/
//添加一个只读的缓存路径(让SDImageCache从bundle中加载预先缓存的图片)
- (void)addReadOnlyCachePath:(nonnull NSString *)path;
#pragma mark - Store Ops
/**
* Asynchronously store an image into memory and disk cache at the given key.
*
* @param image The image to store
* @param key The unique image cache key, usually it's image absolute URL
* @param completionBlock A block executed after the operation is finished
*/
//缓存图片
- (void)storeImage:(nullable UIImage *)image
forKey:(nullable NSString *)key
completion:(nullable SDWebImageNoParamsBlock)completionBlock;
/**
* Asynchronously store an image into memory and disk cache at the given key.
*
* @param image The image to store
* @param key The unique image cache key, usually it's image absolute URL
* @param toDisk Store the image to disk cache if YES
* @param completionBlock A block executed after the operation is finished
*/
//缓存图片 可选内存或磁盘缓存
- (void)storeImage:(nullable UIImage *)image
forKey:(nullable NSString *)key
toDisk:(BOOL)toDisk
completion:(nullable SDWebImageNoParamsBlock)completionBlock;
/**
* Asynchronously store an image into memory and disk cache at the given key.
*
* @param image The image to store
* @param imageData The image data as returned by the server, this representation will be used for disk storage
* instead of converting the given image object into a storable/compressed image format in order
* to save quality and CPU
* @param key The unique image cache key, usually it's image absolute URL
* @param toDisk Store the image to disk cache if YES
* @param completionBlock A block executed after the operation is finished
*/
//NSData数据直接缓存
- (void)storeImage:(nullable UIImage *)image
imageData:(nullable NSData *)imageData
forKey:(nullable NSString *)key
toDisk:(BOOL)toDisk
completion:(nullable SDWebImageNoParamsBlock)completionBlock;
/**
* Synchronously store image NSData into disk cache at the given key.
*
* @warning This method is synchronous, make sure to call it from the ioQueue
*
* @param imageData The image data to store
* @param key The unique image cache key, usually it's image absolute URL
*/
//缓存data数据到磁盘
- (void)storeImageDataToDisk:(nullable NSData *)imageData forKey:(nullable NSString *)key;
#pragma mark - Query and Retrieve Ops
/**
* Async check if image exists in disk cache already (does not load the image)
*
* @param key the key describing the url
* @param completionBlock the block to be executed when the check is done.
* @note the completion block will be always executed on the main queue
*/
//异步检查图片在磁盘缓存中是否存在
- (void)diskImageExistsWithKey:(nullable NSString *)key completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock;
/**
* Operation that queries the cache asynchronously and call the completion when done.
*
* @param key The unique key used to store the wanted image
* @param doneBlock The completion block. Will not get called if the operation is cancelled
*
* @return a NSOperation instance containing the cache op
*/
//异步查询缓存中是否有key值的图片
- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key done:(nullable SDCacheQueryCompletedBlock)doneBlock;
/**
* Query the memory cache synchronously.
*
* @param key The unique key used to store the image
*/
//读取内存缓存图片
- (nullable UIImage *)imageFromMemoryCacheForKey:(nullable NSString *)key;
/**
* Query the disk cache synchronously.
*
* @param key The unique key used to store the image
*/
//读取磁盘缓存图片
- (nullable UIImage *)imageFromDiskCacheForKey:(nullable NSString *)key;
/**
* Query the cache (memory and or disk) synchronously after checking the memory cache.
*
* @param key The unique key used to store the image
*/
//读取缓存图片
- (nullable UIImage *)imageFromCacheForKey:(nullable NSString *)key;
#pragma mark - Remove Ops
/**
* Remove the image from memory and disk cache asynchronously
*
* @param key The unique image cache key
* @param completion A block that should be executed after the image has been removed (optional)
*/
//异步从内存和磁盘缓存中移除图片
- (void)removeImageForKey:(nullable NSString *)key withCompletion:(nullable SDWebImageNoParamsBlock)completion;
/**
* Remove the image from memory and optionally disk cache asynchronously
*
* @param key The unique image cache key
* @param fromDisk Also remove cache entry from disk if YES
* @param completion A block that should be executed after the image has been removed (optional)
*/
//异步移除图片,可选是否移除磁盘缓存
- (void)removeImageForKey:(nullable NSString *)key fromDisk:(BOOL)fromDisk withCompletion:(nullable SDWebImageNoParamsBlock)completion;
#pragma mark - Cache clean Ops
/**
* Clear all memory cached images
*/
//清空内存缓存 异步
- (void)clearMemory;
/**
* Async clear all disk cached images. Non-blocking method - returns immediately.
* @param completion A block that should be executed after cache expiration completes (optional)
*/
//清空磁盘缓存 异步
- (void)clearDiskOnCompletion:(nullable SDWebImageNoParamsBlock)completion;
/**
* Async remove all expired cached image from disk. Non-blocking method - returns immediately.
* @param completionBlock A block that should be executed after cache expiration completes (optional)
*/
//删除过期图片
- (void)deleteOldFilesWithCompletionBlock:(nullable SDWebImageNoParamsBlock)completionBlock;
#pragma mark - Cache Info
/**
* Get the size used by the disk cache
*/
//返回磁盘缓存大小
- (NSUInteger)getSize;
/**
* Get the number of images in the disk cache
*/
//返回磁盘缓存的图片数量
- (NSUInteger)getDiskCount;
/**
* Asynchronously calculate the disk cache's size.
*/
//异步计算磁盘缓存大小
- (void)calculateSizeWithCompletionBlock:(nullable SDWebImageCalculateSizeBlock)completionBlock;
#pragma mark - Cache Paths
/**
* Get the cache path for a certain key (needs the cache path root folder)
*
* @param key the key (can be obtained from url using cacheKeyForURL)
* @param path the cache path root folder
*
* @return the cache path
*/
//读取图片的缓存路径
- (nullable NSString *)cachePathForKey:(nullable NSString *)key inPath:(nonnull NSString *)path;
/**
* Get the default cache path for a certain key
*
* @param key the key (can be obtained from url using cacheKeyForURL)
*
* @return the default cache path
*/
//读取默认缓存路径
- (nullable NSString *)defaultCachePathForKey:(nullable NSString *)key;
@end
SDImageCache.m
#import "SDImageCache.h"
#import "SDWebImageDecoder.h"
#import "UIImage+MultiFormat.h"
#import <CommonCrypto/CommonDigest.h>
#import "UIImage+GIF.h"
#import "NSData+ImageContentType.h"
#import "NSImage+WebCache.h"
// See https://github.com/rs/SDWebImage/pull/1141 for discussion
@interface AutoPurgeCache : NSCache
@end
//NSCache的子类,添加通知 在收到内存警告时移除缓存
@implementation AutoPurgeCache
- (nonnull instancetype)init {
self = [super init];
if (self) {
#if SD_UIKIT
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(removeAllObjects) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
#endif
}
return self;
}
- (void)dealloc {
#if SD_UIKIT
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
#endif
}
@end
FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) {
#if SD_MAC
return image.size.height * image.size.width;
#elif SD_UIKIT || SD_WATCH
return image.size.height * image.size.width * image.scale * image.scale;
#endif
}
@interface SDImageCache ()
#pragma mark - Properties
@property (strong, nonatomic, nonnull) NSCache *memCache;
@property (strong, nonatomic, nonnull) NSString *diskCachePath;
@property (strong, nonatomic, nullable) NSMutableArray<NSString *> *customPaths;
@property (SDDispatchQueueSetterSementics, nonatomic, nullable) dispatch_queue_t ioQueue;
@end
@implementation SDImageCache {
NSFileManager *_fileManager;
}
#pragma mark - Singleton, init, dealloc
+ (nonnull instancetype)sharedImageCache {
static dispatch_once_t once;
static id instance;
dispatch_once(&once, ^{
instance = [self new];
});
return instance;
}
//初始化 默认命名空间default
- (instancetype)init {
return [self initWithNamespace:@"default"];
}
//用指定的命名空间初始化新的SDImageCache
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns {
NSString *path = [self makeDiskCachePath:ns];
return [self initWithNamespace:ns diskCacheDirectory:path];
}
//用指定的命名空间和目录初始化新的SDImageCache
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns
diskCacheDirectory:(nonnull NSString *)directory {
if ((self = [super init])) {
NSString *fullNamespace = [@"com.hackemist.SDWebImageCache." stringByAppendingString:ns];
// Create IO serial queue
//创建IO串行队列
_ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
_config = [[SDImageCacheConfig alloc] init];
// Init the memory cache
//初始化内存缓存
_memCache = [[AutoPurgeCache alloc] init];
_memCache.name = fullNamespace;
// Init the disk cache
//初始化磁盘缓存
if (directory != nil) {
_diskCachePath = [directory stringByAppendingPathComponent:fullNamespace];
} else {
NSString *path = [self makeDiskCachePath:ns];
_diskCachePath = path;
}
//创建fileManager
//这里用同步函数+串行队列有什么意义???
dispatch_sync(_ioQueue, ^{
_fileManager = [NSFileManager new];
});
#if SD_UIKIT
// Subscribe to app events
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(clearMemory)
name:UIApplicationDidReceiveMemoryWarningNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(deleteOldFiles)
name:UIApplicationWillTerminateNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(backgroundDeleteOldFiles)
name:UIApplicationDidEnterBackgroundNotification
object:nil];
#endif
}
return self;
}
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
SDDispatchQueueRelease(_ioQueue);
}
- (void)checkIfQueueIsIOQueue {
const char *currentQueueLabel = dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL);
const char *ioQueueLabel = dispatch_queue_get_label(self.ioQueue);
if (strcmp(currentQueueLabel, ioQueueLabel) != 0) {
NSLog(@"This method should be called from the ioQueue");
}
}
#pragma mark - Cache paths
//添加只读缓存路径
- (void)addReadOnlyCachePath:(nonnull NSString *)path {
if (!self.customPaths) {
self.customPaths = [NSMutableArray new];
}
if (![self.customPaths containsObject:path]) {
[self.customPaths addObject:path];
}
}
//返回缓存路径
- (nullable NSString *)cachePathForKey:(nullable NSString *)key inPath:(nonnull NSString *)path {
NSString *filename = [self cachedFileNameForKey:key];
return [path stringByAppendingPathComponent:filename];
}
//默认缓存路径
- (nullable NSString *)defaultCachePathForKey:(nullable NSString *)key {
return [self cachePathForKey:key inPath:self.diskCachePath];
}
//对key做MD5加密作为文件名
- (nullable NSString *)cachedFileNameForKey:(nullable 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;
}
//设置磁盘缓存路径
- (nullable NSString *)makeDiskCachePath:(nonnull NSString*)fullNamespace {
NSArray<NSString *> *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
return [paths[0] stringByAppendingPathComponent:fullNamespace];
}
#pragma mark - Store Ops
- (void)storeImage:(nullable UIImage *)image
forKey:(nullable NSString *)key
completion:(nullable SDWebImageNoParamsBlock)completionBlock {
[self storeImage:image imageData:nil forKey:key toDisk:YES completion:completionBlock];
}
- (void)storeImage:(nullable UIImage *)image
forKey:(nullable NSString *)key
toDisk:(BOOL)toDisk
completion:(nullable SDWebImageNoParamsBlock)completionBlock {
[self storeImage:image imageData:nil forKey:key toDisk:toDisk completion:completionBlock];
}
//主函数
- (void)storeImage:(nullable UIImage *)image
imageData:(nullable NSData *)imageData
forKey:(nullable NSString *)key
toDisk:(BOOL)toDisk
completion:(nullable SDWebImageNoParamsBlock)completionBlock {
//错误判断
if (!image || !key) {
if (completionBlock) {
completionBlock();
}
return;
}
// if memory cache is enabled
//如果内存缓存可用
if (self.config.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(image); //计算cost
[self.memCache setObject:image forKey:key cost:cost];
}
if (toDisk) { //磁盘缓存
dispatch_async(self.ioQueue, ^{
NSData *data = imageData;
if (!data && image) {
//如果没有data有image,把image转成NSData
SDImageFormat imageFormatFromData = [NSData sd_imageFormatForImageData:data];
data = [image sd_imageDataAsFormat:imageFormatFromData];
}
[self storeImageDataToDisk:data forKey:key]; //磁盘缓存
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock(); //主线程回调
});
}
});
} else {
if (completionBlock) {
completionBlock();
}
}
}
- (void)storeImageDataToDisk:(nullable NSData *)imageData forKey:(nullable NSString *)key {
if (!imageData || !key) {
return;
}
//检查线程是否是io线程,如果不是 提醒
[self checkIfQueueIsIOQueue];
//路径不存在,创建路径
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];
//创建文件
[_fileManager createFileAtPath:cachePathForKey contents:imageData attributes:nil];
// disable iCloud backup
//如果禁用了iCloud备份 标记一下
if (self.config.shouldDisableiCloud) {
[fileURL setResourceValue:@YES forKey:NSURLIsExcludedFromBackupKey error:nil];
}
}
#pragma mark - Query and Retrieve Ops
//异步检查图片在磁盘缓存中是否存在
- (void)diskImageExistsWithKey:(nullable NSString *)key completion:(nullable 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
// .stringByDeletingPathExtension删除扩展名(比如.jpg)
if (!exists) {
exists = [_fileManager fileExistsAtPath:[self defaultCachePathForKey:key].stringByDeletingPathExtension];
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock(exists);
});
}
});
}
//读取内存缓存图片
- (nullable UIImage *)imageFromMemoryCacheForKey:(nullable NSString *)key {
return [self.memCache objectForKey:key];
}
//读取磁盘缓存图片
- (nullable UIImage *)imageFromDiskCacheForKey:(nullable NSString *)key {
UIImage *diskImage = [self diskImageForKey:key];
if (diskImage && self.config.shouldCacheImagesInMemory) { //如果读取到了磁盘缓存的图片且设置有内存缓存,缓存到内存中
NSUInteger cost = SDCacheCostForImage(diskImage);
[self.memCache setObject:diskImage forKey:key cost:cost];
}
return diskImage;
}
//读取缓存图片
- (nullable UIImage *)imageFromCacheForKey:(nullable NSString *)key {
// First check the in-memory cache...
UIImage *image = [self imageFromMemoryCacheForKey:key];
if (image) {
return image;
}
// Second check the disk cache...
image = [self imageFromDiskCacheForKey:key];
return image;
}
//在磁盘缓存中通过key查找NSData数据
- (nullable NSData *)diskImageDataBySearchingAllPathsForKey:(nullable 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;
}
//在自定义路径中查找缓存Data数据
NSArray<NSString *> *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;
}
//磁盘缓存中读取图片
- (nullable UIImage *)diskImageForKey:(nullable NSString *)key {
NSData *data = [self diskImageDataBySearchingAllPathsForKey:key];
if (data) {
UIImage *image = [UIImage sd_imageWithData:data];
image = [self scaledImageForKey:key image:image];
if (self.config.shouldDecompressImages) { //压缩图片
image = [UIImage decodedImageWithImage:image];
}
return image;
}
else {
return nil;
}
}
//处理图片的缩放
- (nullable UIImage *)scaledImageForKey:(nullable NSString *)key image:(nullable UIImage *)image {
return SDScaledImageForKey(key, image);
}
//异步查询缓存中是否有key值的图片
- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key done:(nullable SDCacheQueryCompletedBlock)doneBlock {
//错误判断
if (!key) {
if (doneBlock) {
doneBlock(nil, nil, SDImageCacheTypeNone);
}
return nil;
}
// First check the in-memory cache...
UIImage *image = [self imageFromMemoryCacheForKey:key]; //读取内存缓存图片
if (image) {
NSData *diskData = nil;
//这里为什么要是GIF才返回NSData数据
if ([image isGIF]) {
diskData = [self diskImageDataBySearchingAllPathsForKey:key];
}
if (doneBlock) {
doneBlock(image, diskData, SDImageCacheTypeMemory);
}
return nil;
}
//内存缓存中没有图片,尝试读取磁盘缓存图片
NSOperation *operation = [NSOperation new];
dispatch_async(self.ioQueue, ^{
if (operation.isCancelled) {
// do not call the completion if cancelled
return;
}
@autoreleasepool {
NSData *diskData = [self diskImageDataBySearchingAllPathsForKey:key];
UIImage *diskImage = [self diskImageForKey:key];
if (diskImage && self.config.shouldCacheImagesInMemory) { //如果设置有内存缓存,添加图片到内存
NSUInteger cost = SDCacheCostForImage(diskImage);
[self.memCache setObject:diskImage forKey:key cost:cost];
}
if (doneBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
doneBlock(diskImage, diskData, SDImageCacheTypeDisk);
});
}
}
});
return operation;
}
#pragma mark - Remove Ops
- (void)removeImageForKey:(nullable NSString *)key withCompletion:(nullable SDWebImageNoParamsBlock)completion {
[self removeImageForKey:key fromDisk:YES withCompletion:completion];
}
//移除图片
- (void)removeImageForKey:(nullable NSString *)key fromDisk:(BOOL)fromDisk withCompletion:(nullable SDWebImageNoParamsBlock)completion {
if (key == nil) {
return;
}
if (self.config.shouldCacheImagesInMemory) { //移除内存中图片
[self.memCache removeObjectForKey:key];
}
if (fromDisk) {
dispatch_async(self.ioQueue, ^{ //移除磁盘缓存中图片
[_fileManager removeItemAtPath:[self defaultCachePathForKey:key] error:nil];
if (completion) {
dispatch_async(dispatch_get_main_queue(), ^{
completion();
});
}
});
} else if (completion){
completion();
}
}
# pragma mark - Mem Cache settings
//设置self.memCache
- (void)setMaxMemoryCost:(NSUInteger)maxMemoryCost {
self.memCache.totalCostLimit = maxMemoryCost;
}
- (NSUInteger)maxMemoryCost {
return self.memCache.totalCostLimit;
}
- (NSUInteger)maxMemoryCountLimit {
return self.memCache.countLimit;
}
- (void)setMaxMemoryCountLimit:(NSUInteger)maxCountLimit {
self.memCache.countLimit = maxCountLimit;
}
#pragma mark - Cache clean Ops
//清理内存缓存
- (void)clearMemory {
[self.memCache removeAllObjects];
}
- (void)clearDiskOnCompletion:(nullable SDWebImageNoParamsBlock)completion {
dispatch_async(self.ioQueue, ^{ //删除整个磁盘缓存,重新创建新的路径
[_fileManager removeItemAtPath:self.diskCachePath error:nil];
[_fileManager createDirectoryAtPath:self.diskCachePath
withIntermediateDirectories:YES
attributes:nil
error:NULL];
if (completion) {
dispatch_async(dispatch_get_main_queue(), ^{
completion();
});
}
});
}
- (void)deleteOldFiles {
[self deleteOldFilesWithCompletionBlock:nil];
}
//删除过期的磁盘缓存
- (void)deleteOldFilesWithCompletionBlock:(nullable SDWebImageNoParamsBlock)completionBlock {
dispatch_async(self.ioQueue, ^{
NSURL *diskCacheURL = [NSURL fileURLWithPath:self.diskCachePath isDirectory:YES];
NSArray<NSString *> *resourceKeys = @[NSURLIsDirectoryKey, NSURLContentModificationDateKey, NSURLTotalFileAllocatedSizeKey];
// This enumerator prefetches useful properties for our cache files.
NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtURL:diskCacheURL
includingPropertiesForKeys:resourceKeys
options:NSDirectoryEnumerationSkipsHiddenFiles
errorHandler:NULL];
//计算过期的日期
NSDate *expirationDate = [NSDate dateWithTimeIntervalSinceNow:-self.config.maxCacheAge];
NSMutableDictionary<NSURL *, NSDictionary<NSString *, id> *> *cacheFiles = [NSMutableDictionary dictionary];
NSUInteger currentCacheSize = 0;
// Enumerate all of the files in the cache directory. This loop has two purposes:
//
// 1. Removing files that are older than the expiration date.
// 2. Storing file attributes for the size-based cleanup pass.
//遍历缓存内所有文件
//1.删除过期文件
//2.存储文件属性计算缓存占用
NSMutableArray<NSURL *> *urlsToDelete = [[NSMutableArray alloc] init];
for (NSURL *fileURL in fileEnumerator) {
NSError *error;
NSDictionary<NSString *, id> *resourceValues = [fileURL resourceValuesForKeys:resourceKeys error:&error];
// Skip directories and errors.
if (error || !resourceValues || [resourceValues[NSURLIsDirectoryKey] boolValue]) {
continue;
}
// Remove files that are older than the expiration date;
//把过期的文件路径添加到urlsToDelete数组中
NSDate *modificationDate = resourceValues[NSURLContentModificationDateKey];
if ([[modificationDate laterDate:expirationDate] isEqualToDate:expirationDate]) {
[urlsToDelete addObject:fileURL];
continue;
}
// Store a reference to this file and account for its total size.
//把未被添加进urlsToDelete数组的文件大小添加到总大小中
NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];
currentCacheSize += totalAllocatedSize.unsignedIntegerValue;
cacheFiles[fileURL] = resourceValues;
}
//移除urlsToDelete数组内的缓存文件
for (NSURL *fileURL in urlsToDelete) {
[_fileManager removeItemAtURL:fileURL error:nil];
}
// If our remaining disk cache exceeds a configured maximum size, perform a second
// size-based cleanup pass. We delete the oldest files first.
// 如果剩余的文件大小超过设置的最大缓存大小,优先删除时间最老的文件
if (self.config.maxCacheSize > 0 && currentCacheSize > self.config.maxCacheSize) {
// Target half of our maximum cache size for this cleanup pass.
const NSUInteger desiredCacheSize = self.config.maxCacheSize / 2;
// Sort the remaining cache files by their last modification time (oldest first).
//排序出缓存文件的最后访问时间
NSArray<NSURL *> *sortedFiles = [cacheFiles keysSortedByValueWithOptions:NSSortConcurrent
usingComparator:^NSComparisonResult(id obj1, id obj2) {
return [obj1[NSURLContentModificationDateKey] compare:obj2[NSURLContentModificationDateKey]];
}];
// Delete files until we fall below our desired cache size.
//删除文件直到小于预期的内存大小
for (NSURL *fileURL in sortedFiles) {
if ([_fileManager removeItemAtURL:fileURL error:nil]) {
NSDictionary<NSString *, id> *resourceValues = cacheFiles[fileURL];
NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];
currentCacheSize -= totalAllocatedSize.unsignedIntegerValue;
if (currentCacheSize < desiredCacheSize) {
break;
}
}
}
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock();
});
}
});
}
