遵循于： NSObject
聲明處：SDWebImageDownloaderOperation.h
概述
描述一個下載操作。如果想使用一個自定義的下載操作，需要繼承NSOpertaion并遵循這些協議。
任務
-
- initWithRequest:inSession:options:必須實現 -
- addHandlerForProgress:completed:必須實現 -
shouldDecompressImages:必須實現 -
setShouldDecompressImages:必須實現 -
credential必須實現 -
setCredential:必須實現
實例方法
addHandlersForProgress:completed:
- (nullable id)addHandlersForProgress:(nullable SDWebImageDownloaderProgressBlock)progressBlock completed:(nullable SDWebImageDownloaderCompletedBlock)completedBlock
credential
- (nullable NSURLCredential *)credential
initWithRequest:inSession:options:
- (nonnull instancetype)initWithRequest:(nullable NSURLRequest *)request inSession:(nullable NSURLSession *)session options:(SDWebImageDownloaderOptions)options
setCredential:
- (void)setCredential:(nullable NSURLCredential *)value
setShouldDecompressImages:
- (void)setShouldDecompressImages:(BOOL)value
shouldDecompressImages
- (BOOL)shouldDecompressImages
// END 呵呵噠，文檔中都不需要解析怎么用，只要實現就好的。
