SDWebImage源码解析

2016-07-12 本文已影响98人百省

SDWebImage中核心类如下所示：

26E06FD9-3B94-4AB4-9375-A2E7E5CC4470副本.png

一、SDImageCache
SDImageCache负责缓存图片，包含几个对外属性

//是否解压图片
@property (assign, nonatomic) BOOL shouldDecompressImages;
//iCloud 备份
@property (assign, nonatomic) BOOL shouldDisableiCloud;
//是否能够缓存图片到内存
@property (assign, nonatomic) BOOL shouldCacheImagesInMemory;
//最大内存使用，内存
@property (assign, nonatomic) NSUInteger maxMemoryCost;
//缓存对象的数量最大值
@property (assign, nonatomic) NSUInteger maxMemoryCountLimit;
//缓存时间，默认一周
@property (assign, nonatomic) NSInteger maxCacheAge;
//缓存最大值，磁盘
@property (assign, nonatomic) NSUInteger maxCacheSize;

内部属性:

//缓存对象
@property (strong, nonatomic) NSCache *memCache;
//磁盘缓存路径
@property (strong, nonatomic) NSString *diskCachePath;
//自定义路径数组,如bundle里的图片,可以添加到该数组中
@property (strong, nonatomic) NSMutableArray *customPaths;
//读写队列
@property (SDDispatchQueueSetterSementics, nonatomic) dispatch_queue_t ioQueue;

AutoPurgeCache，当收到内存警告时自动清空缓存

//初始化类的成员变量，监听内存警告、APP退到后台、APP终止通知

(id)initWithNamespace:(NSString *)ns diskCacheDirectory:(NSString *)directory
//根据key值、path值生成文件路径
(NSString *)cachePathForKey:(NSString *)key inPath:(NSString *)path
//根据key值得到文件名
(NSString *)cachedFileNameForKey:(NSString )key
//获取缓存到磁盘的路径
-(NSString )makeDiskCachePath:(NSString)fullNamespace
/存储图片到磁盘
*recalculate表示是否需要把image类型转换为nsdata类型，如果不需要转换则把imageData直接写入磁盘，如果需要转换则把image转换为data
*/

(void)storeImage:(UIImage *)image recalculateFromImage:(BOOL)recalculate imageData:(NSData *)imageData forKey:(NSString *)key toDisk:(BOOL)toDisk
{

if (!image || !key) {
return;
}

if (self.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(image);
[self.memCache setObject:image forKey:key cost:cost];//把图片存储到缓存
}

if (toDisk) {
dispatch_async(self.ioQueue, ^{
NSData *data = imageData;
// image非空才能转换为data
if (image && (recalculate || !data)) {

if TARGET_OS_IPHONE

            //获取图片的alpha信息，判断是否是png图片
            int alphaInfo = CGImageGetAlphaInfo(image.CGImage);
            BOOL hasAlpha = !(alphaInfo == kCGImageAlphaNone ||
                              alphaInfo == kCGImageAlphaNoneSkipFirst ||
                              alphaInfo == kCGImageAlphaNoneSkipLast);
            BOOL imageIsPng = hasAlpha;
            
            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

        }            
        // 把data写入磁盘
        if (data) {
            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:data attributes:nil];
            
            // disable iCloud backup
            if (self.shouldDisableiCloud) {
                [fileURL setResourceValue:[NSNumber numberWithBool:YES] forKey:NSURLIsExcludedFromBackupKey error:nil];
            }
        }
    });
}

}
</code></pre>

//查询图片是否已存在

(BOOL)diskImageExistsWithKey:(NSString *)key;

(void)diskImageExistsWithKey:(NSString *)key completion:(SDWebImageCheckCacheCompletionBlock)completionBlock;

//从缓存中取图片

(UIImage *)imageFromMemoryCacheForKey:(NSString *)key
//从磁盘中取图片，先从内存缓存中取，无则从磁盘中取
(UIImage *)imageFromDiskCacheForKey:(NSString *)key
//根据key生成文件路径，先从默认图片路径中查找，无则从自定义路径中查找，返回image的data数据
(NSData *)diskImageDataBySearchingAllPathsForKey:(NSString *)key;
//根据key找到image
(UIImage *)diskImageForKey:(NSString *)key;
//根据key中后缀@2x、@3x，放大图片到2、3倍
(UIImage *)scaledImageForKey:(NSString *)key image:(UIImage *)image;

<pre><code>//在磁盘中查找图片

(NSOperation *)queryDiskCacheForKey:(NSString *)key done:(SDWebImageQueryCompletedBlock)doneBlock { if (!doneBlock) { return nil;
}
if (!key) { doneBlock(nil, SDImageCacheTypeNone); return nil;
}
// First check the in-memory cache... UIImage *image = [self imageFromMemoryCacheForKey:key]; if (image) { doneBlock(image, SDImageCacheTypeMemory); return nil;
}
<code><pre>
```
 //缓存中没有，则从硬盘查找，放在ioQueue中处理
```
NSOperation *operation = [NSOperation new]; dispatch_async(self.ioQueue, ^{ if (operation.isCancelled) { return; } @autoreleasepool { UIImage *diskImage = [self diskImageForKey:key]; if (diskImage && self.shouldCacheImagesInMemory) { NSUInteger cost = SDCacheCostForImage(diskImage); [self.memCache setObject:diskImage forKey:key cost:cost]; } dispatch_async(dispatch_get_main_queue(), ^{ doneBlock(diskImage, SDImageCacheTypeDisk); }); } }); return operation;
}

//从缓存中移除图片，

(void)removeImageForKey:(NSString *)key fromDisk:(BOOL)fromDisk withCompletion:(SDWebImageNoParamsBlock)completion { if (key == nil) { return; } if (self.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();
}
}
//从磁盘中移除缓存图片文件夹
(void)clearDiskOnCompletion:(SDWebImageNoParamsBlock)completion;
//每次退到后台，清除已过期文件，并判断缓存文件夹是否大于设置的最大容量

(void)cleanDiskWithCompletionBlock:(SDWebImageNoParamsBlock)completionBlock {
dispatch_async(self.ioQueue, ^{
//初始化缓存路径URL
NSURL *diskCacheURL = [NSURL fileURLWithPath:self.diskCachePath isDirectory:YES];
//获取路径下文件的属性值，目录、文件修改日期、文件大小
NSArray *resourceKeys = @[NSURLIsDirectoryKey, NSURLContentModificationDateKey, NSURLTotalFileAllocatedSizeKey];

  // 枚举器预先获取缓存文件的有用的属性
  NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtURL:diskCacheURL                                                   includingPropertiesForKeys:resourceKeys                                                                      options:NSDirectoryEnumerationSkipsHiddenFiles                                                                 errorHandler:NULL];        NSDate *expirationDate = [NSDate dateWithTimeIntervalSinceNow:-self.maxCacheAge];        NSMutableDictionary *cacheFiles = [NSMutableDictionary dictionary];
  NSUInteger currentCacheSize = 0;

  NSMutableArray *urlsToDelete = [[NSMutableArray alloc] init];

for (NSURL *fileURL in fileEnumerator) {
NSDictionary *resourceValues = [fileURL resourceValuesForKeys:resourceKeys error:NULL];

      // 是文件夹目录
      if ([resourceValues[NSURLIsDirectoryKey] boolValue]) {                continue;            }

      // 文件最后一次修改的日期与过期日期比较谁更晚，laterDate函数返回两个日期中较晚的一个时间，如果修改日期小于过期日期则删除该文件
      NSDate *modificationDate = resourceValues[NSURLContentModificationDateKey];            if ([[modificationDate laterDate:expirationDate] isEqualToDate:expirationDate]) {                [urlsToDelete addObject:fileURL];                continue;            }

      // 统计未过期文件的大小
      NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];            currentCacheSize += [totalAllocatedSize unsignedIntegerValue];            [cacheFiles setObject:resourceValues forKey:fileURL];
  }
  // 删除已过期文件
  for (NSURL *fileURL in urlsToDelete) {                 
  [_fileManager removeItemAtURL:fileURL error:nil];          
  }

  // 如果缓存文件容量已经大于设置的容量则删除最早的文件
  if (self.maxCacheSize > 0 && currentCacheSize > self.maxCacheSize) {
      // 最大缓存容量的一半
      const NSUInteger desiredCacheSize = self.maxCacheSize / 2;

      // 由修改日期对文件排序
      NSArray *sortedFiles = [cacheFiles keysSortedByValueWithOptions:NSSortConcurrent      
                                  usingComparator:^NSComparisonResult(id obj1, id obj2) {                                                                
       return [obj1[NSURLContentModificationDateKey] compare:obj2[NSURLContentModificationDateKey]];                                                            }];

      //删除文件直到文件夹的容量 < 最大容量的一半
      for (NSURL *fileURL in sortedFiles) {                 
      if ([_fileManager removeItemAtURL:fileURL error:nil]) {   
             NSDictionary *resourceValues = cacheFiles[fileURL];                     
             NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];    
             currentCacheSize -= [totalAllocatedSize unsignedIntegerValue];                      
            if (currentCacheSize < desiredCacheSize) {                          
               break;   
             }   
         }

}
}

if (completionBlock) {

dispatch_async(dispatch_get_main_queue(), ^{

completionBlock(); }); } });
}

// 获取已缓存文件的总容量

(NSUInteger)getSize { __blockNSUInteger size = 0; dispatch_sync(self.ioQueue, ^{ NSDirectoryEnumerator *fileEnumerator = [_fileManagerenumeratorAtPath:self.diskCachePath]; for (NSString *fileName in fileEnumerator) { NSString *filePath = [self.diskCachePathstringByAppendingPathComponent:fileName]; NSDictionary *attrs = [[NSFileManagerdefaultManager] attributesOfItemAtPath:filePath error:nil]; size += [attrs fileSize]; } }); return size;}

// 获取已缓存图片的总数量

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

// 计算文件大小及文件数量

(void)calculateSizeWithCompletionBlock:(SDWebImageCalculateSizeBlock)completionBlock { NSURL *diskCacheURL = [NSURLfileURLWithPath:self.diskCachePathisDirectory:YES]; dispatch_async(self.ioQueue, ^{ NSUInteger fileCount = 0; NSUInteger totalSize = 0; NSDirectoryEnumerator *fileEnumerator = [_fileManagerenumeratorAtURL:diskCacheURL includingPropertiesForKeys:@[NSFileSize] options:NSDirectoryEnumerationSkipsHiddenFiles errorHandler:NULL]; for (NSURL *fileURL in fileEnumerator) { NSNumber *fileSize; [fileURL getResourceValue:&fileSize forKey:NSURLFileSizeKeyerror:NULL]; totalSize += [fileSize unsignedIntegerValue]; fileCount += 1; } if (completionBlock) { dispatch_async(dispatch_get_main_queue(), ^{ completionBlock(fileCount, totalSize); }); } });
}

SDWebImage源码解析

if TARGET_OS_IPHONE

else

endif

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