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第六篇

前言

我們在SDWebImageCache(上)中了解了這個緩存類大概的功能是什么？那么接下來就要看看這些功能是如何實(shí)現(xiàn)的？再次強(qiáng)調(diào)，不管是圖片的緩存還是其他各種不同形式的緩存，在原理上都極其相似，我們通過SDWebImageCache,來看看作者是如何實(shí)現(xiàn)這個功能的。

在業(yè)務(wù)中，經(jīng)常要緩存數(shù)據(jù)，通過本篇的學(xué)習(xí)，我們寫出的緩存管理者這個管理者對象，就能夠有所進(jìn)步。

NSCache

對于很多開發(fā)者來說，NSCache是一個陌生人，因?yàn)榇蠹彝鶎SMutableDictionary情有獨(dú)鐘。可憐的 NSCache 一直處于 NSMutableDictionary 的陰影之下。就好像沒有人知道它提供了垃圾處理的功能，而開發(fā)者們卻費(fèi)勁力氣地去自己實(shí)現(xiàn)它。

沒錯，NSCache 基本上就是一個會自動移除對象來釋放內(nèi)存的 NSMutableDictionary。無需響應(yīng)內(nèi)存警告或者使用計(jì)時器來清除緩存。唯一的不同之處是鍵對象不會像 NSMutableDictionary 中那樣被復(fù)制，這實(shí)際上是它的一個優(yōu)點(diǎn)（鍵不需要實(shí)現(xiàn) NSCopying 協(xié)議）。

當(dāng)有緩存數(shù)據(jù)到內(nèi)存的業(yè)務(wù)的時候，就應(yīng)該考慮NSCache了，有緩存就有清楚緩存。

NSCache 每個方法和屬性的具體作用，請參考這篇文章NSCache

AutoPurgeCache

NSCache在收到內(nèi)存警告的時候會釋放自身的一部分資源，設(shè)計(jì)AutoPurgeCache的目的是在收到警告時，釋放緩存的所有資源。

通過繼承自NSCache,監(jiān)聽UIApplicationDidReceiveMemoryWarningNotification來實(shí)現(xiàn)。

@interface AutoPurgeCache : NSCache
@end

@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

計(jì)算一個UIImage的SDCacheCost

圖片在該緩存中的大小是通過像素來衡量的。

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
}

** 注意：FOUNDATION_STATIC_INLINE表示該函數(shù)是一個具有文件內(nèi)部訪問權(quán)限的內(nèi)聯(lián)函數(shù)，所謂的內(nèi)聯(lián)函數(shù)就是建議編譯器在調(diào)用時將函數(shù)展開。建議的意思就是說編譯器不一定會按照你的建議做。因此內(nèi)聯(lián)函數(shù)盡量不要寫的太復(fù)雜。**

Properties

SDWebImageCache實(shí)現(xiàn)部分有下邊幾個屬性：

#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;
}

memCache 內(nèi)存容器
diskCachePath 硬盤緩存路徑
customPaths 自定義的讀取路徑，這是一個數(shù)組，我們可以通過addReadOnlyCachePath:這個方法往里邊添加路徑。當(dāng)我們讀取讀片的時候，這個數(shù)組的路徑也會作為數(shù)據(jù)源
ioQueue 稱作輸入輸出隊(duì)列，隊(duì)列往往可以當(dāng)做一種“鎖”來使用，我們把某些任務(wù)按照順利一步一步的進(jìn)行，必須考慮線程是否安全
_fileManager 文件管理者，這個就不多說了，大家都知道怎么用

初始化

這一部分關(guān)系到Singleton, init, dealloc這三個方面的代碼，初始化有四個方法，我們重點(diǎn)講解最后一個初始化方法（這也是作者建議的方法，其他方法通過該方法實(shí)現(xiàn)）：

+ (nonnull instancetype)sharedImageCache
- (instancetype)init
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns
                       diskCacheDirectory:(nonnull NSString *)directory

- (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
        _ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
        
        _config = [[SDImageCacheConfig alloc] init];
        
        // 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;
        }

        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;
}

這個方法其實(shí)就做了兩件事：1.初始化自身的屬性 2.添加通知監(jiān)聽。其他的初始化代碼在這里就不寫了。

Cache paths

1.添加自定義路徑

- (void)addReadOnlyCachePath:(nonnull NSString *)path {
    if (!self.customPaths) {
        self.customPaths = [NSMutableArray new];
    }

    if (![self.customPaths containsObject:path]) {
        [self.customPaths addObject:path];
    }
}

2.文件名（MD5）

- (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;
}

3.默認(rèn)的某個圖片的路徑

- (nullable NSString *)defaultCachePathForKey:(nullable NSString *)key {
    return [self cachePathForKey:key inPath:self.diskCachePath];
}

4.根據(jù)名稱和路徑拼接路徑

- (nullable NSString *)cachePathForKey:(nullable NSString *)key inPath:(nonnull NSString *)path {
    NSString *filename = [self cachedFileNameForKey:key];
    return [path stringByAppendingPathComponent:filename];
}

Store Image

保存圖片也有四個方法，我們按照順序來看：

1.保存數(shù)據(jù)到Disk

- (void)storeImageDataToDisk:(nullable NSData *)imageData forKey:(nullable NSString *)key {
    if (!imageData || !key) {
        return;
    }
    
    [self checkIfQueueIsIOQueue];
    
    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.config.shouldDisableiCloud) {
        [fileURL setResourceValue:@YES forKey:NSURLIsExcludedFromBackupKey error:nil];
    }
}

檢查imageData或者key是否為nil
檢查是否在自身的隊(duì)列中進(jìn)行的操作
創(chuàng)建Disk緩存文件夾
根據(jù)key獲取默認(rèn)的緩存路徑
將數(shù)據(jù)寫入到上邊獲取的路徑中
根據(jù)配置文件設(shè)置是否禁用iCloud的備份功能

2.參數(shù)最多的保存圖片的方法

- (void)storeImage:(nullable UIImage *)image
         imageData:(nullable NSData *)imageData
            forKey:(nullable NSString *)key
            toDisk:(BOOL)toDisk
        completion:(nullable SDWebImageNoParamsBlock)completionBlock {
    if (!image || !key) {
        if (completionBlock) {
            completionBlock();
        }
        return;
    }
    // if memory cache is enabled
    if (self.config.shouldCacheImagesInMemory) {
        NSUInteger cost = SDCacheCostForImage(image);
        [self.memCache setObject:image forKey:key cost:cost];
    }
    
    if (toDisk) {
        dispatch_async(self.ioQueue, ^{
            NSData *data = imageData;
            
            if (!data && image) {
                SDImageFormat imageFormatFromData = [NSData sd_imageFormatForImageData:data];
                data = [image sd_imageDataAsFormat:imageFormatFromData];
            }
            
            [self storeImageDataToDisk:data forKey:key];
            if (completionBlock) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    completionBlock();
                });
            }
        });
    } else {
        if (completionBlock) {
            completionBlock();
        }
    }
}

檢查image或者key是否為nil
根據(jù)配置文件中是否設(shè)置了緩存到內(nèi)存，保存image到緩存中，這個過程是非?？斓?，因此不用考慮線程
如果保存到Disk，創(chuàng)建異步串行隊(duì)列 我們把數(shù)據(jù)保存到Disk，其實(shí)保存的應(yīng)該是數(shù)據(jù)的二進(jìn)制文件
保存二進(jìn)制數(shù)據(jù)到Disk，如果不存在，需要把image轉(zhuǎn)換成NSData
調(diào)用Block

3.其他兩個保存的方法

- (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];
}

Query and Retrieve 數(shù)據(jù)

1.根據(jù)key判斷Disk中的數(shù)據(jù)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
        if (!exists) {
            exists = [_fileManager fileExistsAtPath:[self defaultCachePathForKey:key].stringByDeletingPathExtension];
        }

        if (completionBlock) {
            dispatch_async(dispatch_get_main_queue(), ^{
                completionBlock(exists);
            });
        }
    });
}

2.獲取緩存到內(nèi)存中的數(shù)據(jù)

- (nullable UIImage *)imageFromMemoryCacheForKey:(nullable NSString *)key {
    return [self.memCache objectForKey:key];
}

3.獲取Disk中的數(shù)據(jù)

在Disk中獲取數(shù)據(jù)跟在內(nèi)存中獲取不一樣，內(nèi)存中直接保存的是UIImage，而Disk中保存的是NSData，因此肯定需要一個NSData -> UIImage 的轉(zhuǎn)換過程。接下來我們看看這個轉(zhuǎn)換過程：

根據(jù)key獲取Disk中的NSData數(shù)據(jù)，總體思路就是先從默認(rèn)的路徑獲取，如果沒有獲取到，再從自定義的路徑獲取，值得注意的是，要考慮沒有pathExtention的情況

  - (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;
      }
  
      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;
  }

根據(jù)NSData 獲取 UIImage，需要scaled圖片，根據(jù)配置文件的設(shè)置，是否解壓圖片

  - (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) {
              image = [UIImage decodedImageWithImage:image];
          }
          return image;
      }
      else {
          return nil;
      }
  }

將UIImage 放入內(nèi)存，返回圖片

  - (nullable UIImage *)imageFromDiskCacheForKey:(nullable NSString *)key {
      UIImage *diskImage = [self diskImageForKey:key];
      if (diskImage && self.config.shouldCacheImagesInMemory) {
          NSUInteger cost = SDCacheCostForImage(diskImage);
          [self.memCache setObject:diskImage forKey:key cost:cost];
      }
  
      return diskImage;
  }

4.先獲取內(nèi)存的數(shù)據(jù)，如果沒有，在獲取Disk的數(shù)據(jù)

- (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;
}

5.異步獲取數(shù)據(jù)

上邊1.2.3.4 中獲取數(shù)據(jù)的方法都不是異步獲取的，在SDWebImageCache中，涉及到異步獲取的，都會通過Block來回調(diào)的。

這個異步獲取值得說的有兩點(diǎn)：

如果在內(nèi)存中獲取到的圖片是GIF，那么要去Disk中獲取
為什么要返回一個NSOperation對象呢？其實(shí)我們可以通過這個NSOperation對象取消獲取任務(wù)

代碼：

- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key done:(nullable SDCacheQueryCompletedBlock)doneBlock {
    if (!key) {
        if (doneBlock) {
            doneBlock(nil, nil, SDImageCacheTypeNone);
        }
        return nil;
    }

    // First check the in-memory cache...
    UIImage *image = [self imageFromMemoryCacheForKey:key];
    if (image) {
        NSData *diskData = nil;
        if ([image isGIF]) {
            diskData = [self diskImageDataBySearchingAllPathsForKey:key];
        }
        if (doneBlock) {
            doneBlock(image, diskData, SDImageCacheTypeMemory);
        }
        return nil;
    }

    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) {
                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;
}

Remove 數(shù)據(jù)

- (void)removeImageForKey:(nullable NSString *)key withCompletion:(nullable SDWebImageNoParamsBlock)completion {
    [self removeImageForKey:key fromDisk:YES withCompletion:completion];
}

- (void)removeImageForKey:(nullable NSString *)key fromDisk:(BOOL)fromDisk withCompletion:(nullable SDWebImageNoParamsBlock)completion {
    if (key == nil) {
        return;
    }

    if (self.config.shouldCacheImagesInMemory) {
        [self.memCache removeObjectForKey:key];
    }

    if (fromDisk) {
        dispatch_async(self.ioQueue, ^{
            [_fileManager removeItemAtPath:[self defaultCachePathForKey:key] error:nil];
            
            if (completion) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    completion();
                });
            }
        });
    } else if (completion){
        completion();
    }
    
}

Mem Cache settings

- (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;
}

清空數(shù)據(jù)

清空數(shù)據(jù)有值得我們注意的地方，我們一個一個方法的看：

1.清空內(nèi)存緩存數(shù)據(jù)

- (void)clearMemory {
    [self.memCache removeAllObjects];
}

2.清空Disk數(shù)據(jù)

- (void)clearDiskOnCompletion:(nullable SDWebImageNoParamsBlock)completion {
    dispatch_async(self.ioQueue, ^{
        [_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();
            });
        }
    });
}

3.清空舊數(shù)據(jù)

對于清空舊數(shù)據(jù)而言，我們需要考慮兩個方面：

首先要清空掉所有的過期的數(shù)據(jù)
過期的數(shù)據(jù)清空后，緩存的數(shù)據(jù)比我們設(shè)置的最大緩存量還大，我們要繼續(xù)清空數(shù)據(jù)，直到滿足我們的需求為止

這里邊大概用到的思路就是上邊說的兩點(diǎn)，關(guān)鍵是如何實(shí)現(xiàn)上邊所說的內(nèi)容。有一些我們平時可能不太接觸的知識點(diǎn)，在這里做一些簡要的講解

首先我們需要遍歷Disk緩存路徑下的所有文件，那么我們怎么遍歷呢？NSFileManager有一個很好地方法：

返回一個NSDirectoryEnumerator<NSURL *> * 這個對象中存放的是NSURLs
url 需要遍歷的路徑
(nullable NSArray<NSURLResourceKey> \*)keys 這個需要傳入一個數(shù)組，表示想獲取的NSURLResourceKeys，我們來看看這個NSURLResourceKey: 點(diǎn)進(jìn)去看了下。太長了，在這里就不copy了。有興趣的同學(xué)，自己去看看，太長了。我們就說說著這個清空方法中用到的把：
- NSURLIsDirectoryKey 是否是文件夾
- NSURLContentModificationDateKey 最后修改時間
- NSURLTotalFileAllocatedSizeKey 分配的尺寸
options:(NSDirectoryEnumerationOptions)mask 傳入過濾參數(shù)，這里NSDirectoryEnumerationSkipsHiddenFiles 是指忽略隱藏文件

其次，我們有了這些參數(shù)了。在根據(jù)最后修改日期是否過期，刪除掉過期的數(shù)據(jù)就行了。還有一個值得我們注意的就是如何對一個字典進(jìn)行排序：

NSArray<NSURL *> *sortedFiles = [cacheFiles keysSortedByValueWithOptions:NSSortConcurrent
                                                                     usingComparator:^NSComparisonResult(id obj1, id obj2) {
                                                                         return [obj1[NSURLContentModificationDateKey] compare:obj2[NSURLContentModificationDateKey]];
                                                                     }];

這個會返回排好序的字典的所有的key。NSSortConcurrent是并發(fā)排序，效率高，但可能不穩(wěn)定，NSSortStable 穩(wěn)定，但可能效率不如NSSortConcurrent高。排序的規(guī)則通過Block指定。

好了，基本要注意的就這些。這個函數(shù)的實(shí)現(xiàn)也是基于這種思路。

- (void)deleteOldFiles {
    [self deleteOldFilesWithCompletionBlock:nil];
}

- (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];

        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.
        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;
            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.
            NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];
            currentCacheSize += totalAllocatedSize.unsignedIntegerValue;
            cacheFiles[fileURL] = resourceValues;
        }
        
        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.
        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).
            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.
            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();
            });
        }
    });
}

申請一段時間在后臺刪除舊數(shù)據(jù)

- (void)backgroundDeleteOldFiles {
    Class UIApplicationClass = NSClassFromString(@"UIApplication");
    if(!UIApplicationClass || ![UIApplicationClass respondsToSelector:@selector(sharedApplication)]) {
        return;
    }
    UIApplication *application = [UIApplication performSelector:@selector(sharedApplication)];
    __block UIBackgroundTaskIdentifier bgTask = [application beginBackgroundTaskWithExpirationHandler:^{
        // Clean up any unfinished task business by marking where you
        // stopped or ending the task outright.
        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];

    // Start the long-running task and return immediately.
    [self deleteOldFilesWithCompletionBlock:^{
        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];
}

Cache Info

- (NSUInteger)getSize {
    __block NSUInteger size = 0;
    dispatch_sync(self.ioQueue, ^{
        NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtPath:self.diskCachePath];
        for (NSString *fileName in fileEnumerator) {
            NSString *filePath = [self.diskCachePath stringByAppendingPathComponent:fileName];
            NSDictionary<NSString *, id> *attrs = [[NSFileManager defaultManager] attributesOfItemAtPath:filePath error:nil];
            size += [attrs fileSize];
        }
    });
    return size;
}

- (NSUInteger)getDiskCount {
    __block NSUInteger count = 0;
    dispatch_sync(self.ioQueue, ^{
        NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtPath:self.diskCachePath];
        count = fileEnumerator.allObjects.count;
    });
    return count;
}

- (void)calculateSizeWithCompletionBlock:(nullable SDWebImageCalculateSizeBlock)completionBlock {
    NSURL *diskCacheURL = [NSURL fileURLWithPath:self.diskCachePath isDirectory:YES];

    dispatch_async(self.ioQueue, ^{
        NSUInteger fileCount = 0;
        NSUInteger totalSize = 0;

        NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtURL:diskCacheURL
                                                   includingPropertiesForKeys:@[NSFileSize]
                                                                      options:NSDirectoryEnumerationSkipsHiddenFiles
                                                                 errorHandler:NULL];

        for (NSURL *fileURL in fileEnumerator) {
            NSNumber *fileSize;
            [fileURL getResourceValue:&fileSize forKey:NSURLFileSizeKey error:NULL];
            totalSize += fileSize.unsignedIntegerValue;
            fileCount += 1;
        }

        if (completionBlock) {
            dispatch_async(dispatch_get_main_queue(), ^{
                completionBlock(fileCount, totalSize);
            });
        }
    });
}

總結(jié)

SDWebImageCache 就寫完了，本篇算是長文了，對于那種圖片比較多的app，實(shí)現(xiàn)一個自己的緩存類還是很有必要的。

由于個人知識有限，如有錯誤之處，還望各路大俠給予指出啊

SDWebImage源碼解讀之 NSData+ImageContentType 簡書博客園
SDWebImage源碼解讀之 UIImage+GIF 簡書博客園
SDWebImage源碼解讀之 SDWebImageCompat 簡書博客園
SDWebImage源碼解讀之SDWebImageDecoder 簡書博客園
SDWebImage源碼解讀之SDWebImageCache(上) 簡書博客園

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SDWebImage源碼解讀之SDWebImageCache(下)

SDWebImage源碼解讀之SDWebImageCache(下)

前言

NSCache

AutoPurgeCache

計(jì)算一個UIImage的SDCacheCost

Properties

初始化

Cache paths

1.添加自定義路徑

2.文件名（MD5）

3.默認(rèn)的某個圖片的路徑

4.根據(jù)名稱和路徑拼接路徑

Store Image

1.保存數(shù)據(jù)到Disk

2.參數(shù)最多的保存圖片的方法

3.其他兩個保存的方法

Query and Retrieve 數(shù)據(jù)

1.根據(jù)key判斷Disk中的數(shù)據(jù)是否存在

2.獲取緩存到內(nèi)存中的數(shù)據(jù)

3.獲取Disk中的數(shù)據(jù)

4.先獲取內(nèi)存的數(shù)據(jù)，如果沒有，在獲取Disk的數(shù)據(jù)

5.異步獲取數(shù)據(jù)

Remove 數(shù)據(jù)

Mem Cache settings

清空數(shù)據(jù)

1.清空內(nèi)存緩存數(shù)據(jù)

2.清空Disk數(shù)據(jù)

3.清空舊數(shù)據(jù)

Cache Info

總結(jié)

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

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SDWebImage源碼解讀之SDWebImageCache(下)

前言

NSCache

AutoPurgeCache

計(jì)算一個UIImage的SDCacheCost

Properties

初始化

Cache paths

1.添加自定義路徑

2.文件名（MD5）

3.默認(rèn)的某個圖片的路徑

4.根據(jù)名稱和路徑拼接路徑

Store Image

1.保存數(shù)據(jù)到Disk

2.參數(shù)最多的保存圖片的方法

3.其他兩個保存的方法

Query and Retrieve 數(shù)據(jù)

1.根據(jù)key判斷Disk中的數(shù)據(jù)是否存在

2.獲取緩存到內(nèi)存中的數(shù)據(jù)

3.獲取Disk中的數(shù)據(jù)

4.先獲取內(nèi)存的數(shù)據(jù)，如果沒有，在獲取Disk的數(shù)據(jù)

5.異步獲取數(shù)據(jù)

Remove 數(shù)據(jù)

Mem Cache settings

清空數(shù)據(jù)

1.清空內(nèi)存緩存數(shù)據(jù)

2.清空Disk數(shù)據(jù)

3.清空舊數(shù)據(jù)

Cache Info

總結(jié)

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九欧美,1769亚洲,黄色成人av

4.先獲取內(nèi)存的數(shù)據(jù)，如果沒有，在獲取Disk的數(shù)據(jù)