无限互联SDWebImage图片缓存流程分析

1、【无限互联】sdwebimage图片缓存流程分析sdwebimage是一个功能很强大的缓存网络图片的框架。框架实现了异步加载网络图片、自动缓存图片数据等功能。以uiimageview加载网络图片为例，对其总体的加载图片流程做一个大致的分析。 首先使用sdwebimage先要导入 #import uiimageview+webcache.h文件，设置网络图片的图片地址就可以加载图片。objc view plaincopyprint?1. nsurl *url = nsurl urlwithstring: 2. imageview setimagewithurl:url; 根据网络图片地址，sdw

2、ebimagemanager类提供了方法downloadwithurl加载图片objc view plaincopyprint?1. id operation = sdwebimagemanager.sharedmanager downloadwithurl:url options:options progress:progressblock completed:(uiimage *image, nserror *error, sdimagecachetype cachetype, bool finished) 2. if (!wself) return; 3. dispatch_main_s

3、ync_safe( 4. if (!wself) return; 5. if (image) 6. wself.image = image; 7. wself setneedslayout; 8. 9. if (completedblock & finished) 10. completedblock(image, error, cachetype); 11. 12. ); 13. ; 14. objc_setassociatedobject(self, &operationkey, operation, objc_association_retain_nonatomic); 15. id o

4、peration = sdwebimagemanager.sharedmanager downloadwithurl:url options:options progress:progressblock completed:(uiimage *image, nserror *error, sdimagecachetype cachetype, bool finished) if (!wself) return; dispatch_main_sync_safe( if (!wself) return; if (image) wself.image = image; wself setneedsl

5、ayout; if (completedblock & finished) completedblock(image, error, cachetype); ); ; objc_setassociatedobject(self, &operationkey, operation, objc_association_retain_nonatomic); 进入downloadwithurl方法,由sdimagercache类提供方法querydiskcacheforkey检查内存中是否有图片缓存，如果有图片缓存，回调block将图片数据传递给sdwebimagemanger类。sdwebimage

6、mange类回调block将图片数据传递给uiimageview+webcache类去显示图片。objc view plaincopyprint?1. uiimage *image = self imagefrommemorycacheforkey:key; 2. if (image) 3. doneblock(image, sdimagecachetypememory); 4. return nil; 5. uiimage *image = self imagefrommemorycacheforkey:key; if (image) doneblock(image, sdimagecach

7、etypememory); return nil; 如果内存中没有图片缓存，将会去磁盘中查找图片缓存。这一步操作是异步操作，如果从磁盘中读取到图片数据，将图片数据添加到内存缓存中，回调block将图片数据传递给sdwebimagemanger类。 sdwebimagemange类回调block将图片数据传递给uiimageview+webcache类去显示图片objc view plaincopyprint?1. dispatch_async(self.ioqueue, 2. if (operation.iscancelled) 3. return; 4. 5.6. autoreleasepo

8、ol 7. uiimage *diskimage = self diskimageforkey:key; 8. if (diskimage) 9. cgfloat cost = diskimage.size.height * diskimage.size.width * diskimage.scale; 10. self.memcache setobject:diskimage forkey:key cost:cost; 11. 12.13. dispatch_async(dispatch_get_main_queue(), 14. doneblock(diskimage, sdimageca

9、chetypedisk); 15. ); 16. dispatch_async(self.ioqueue, if (operation.iscancelled) return; autoreleasepool uiimage *diskimage = self diskimageforkey:key; if (diskimage) cgfloat cost = diskimage.size.height * diskimage.size.width * diskimage.scale; self.memcache setobject:diskimage forkey:key cost:cost

10、; dispatch_async(dispatch_get_main_queue(), doneblock(diskimage, sdimagecachetypedisk); ); 内存和磁盘中都没有图片缓存，由sdwebimagedownloader类downloadimagewithurl方法请求网络下载图片。objc view plaincopyprint?1. - (id )downloadimagewithurl:(nsurl *)url options:(sdwebimagedownloaderoptions)options progress:(void ()(nsinteger,

11、 nsinteger)progressblock completed:(void ()(uiimage *, nsdata *, nserror *, bool)completedblock 2. - (id )downloadimagewithurl:(nsurl *)url options:(sdwebimagedownloaderoptions)options progress:(void ()(nsinteger, nsinteger)progressblock completed:(void ()(uiimage *, nsdata *, nserror *, bool)comple

12、tedblock 图片下载完成后，数据下载完成后交给 sdwebimagedecoder 做图片解码处理,图片解码完成后回调给sdwebimagedownloader类，sdwebimagedownloader类，回调block将图片数据传递给sdwebimagemanger类。 sdwebimagemange类回调block将图片数据传递给uiimageview+webcache类显示图片。图片数据会写入到内存和磁盘缓存中。图片数据写入磁盘缓存中是异步操作，避免拖慢主线程。objc view plaincopyprint?1. - (void)storeimage:(uiimage *)im

13、age recalculatefromimage:(bool)recalculate imagedata:(nsdata *)imagedata forkey:(nsstring *)key todisk:(bool)todisk 2. if (!image | !key) 3. return; 4. 5. self.memcache setobject:image forkey:key cost:image.size.height * image.size.width * image.scale; 6. if (todisk) 7. dispatch_async(self.ioqueue,

14、8. nsdata *data = imagedata; 9.10. if (image & (recalculate | !data) 11. bool imageispng = yes; 12. if (imagedata length = kpngsignaturedata length) 13. imageispng = imagedatahaspngpreffix(imagedata); 14. 15. if (imageispng) 16. data = uiimagepngrepresentation(image); 17. 18. else 19. data = uiimage

15、jpegrepresentation(image, (cgfloat)1.0); 20. 21. data = nsbitmapimagerep representationofimagerepsinarray:image.representations usingtype: nsjpegfiletype properties:nil; 22. 23. if (data) 24. if (!_filemanager fileexistsatpath:_diskcachepath) 25. _filemanager createdirectoryatpath:_diskcachepath wit

16、hintermediatedirectories:yes attributes:nil error:null; 26. 27. _filemanager createfileatpath:self defaultcachepathforkey:key contents:data attributes:nil; 28. 29. ); 30. 31. - (void)storeimage:(uiimage *)image recalculatefromimage:(bool)recalculate imagedata:(nsdata *)imagedata forkey:(nsstring *)k

17、ey todisk:(bool)todisk if (!image | !key) return; self.memcache setobject:image forkey:key cost:image.size.height * image.size.width * image.scale; if (todisk) dispatch_async(self.ioqueue, nsdata *data = imagedata; if (image & (recalculate | !data) bool imageispng = yes; if (imagedata length = kpngs

18、ignaturedata length) imageispng = imagedatahaspngpreffix(imagedata); if (imageispng) data = uiimagepngrepresentation(image); else data = uiimagejpegrepresentation(image, (cgfloat)1.0); data = nsbitmapimagerep representationofimagerepsinarray:image.representations usingtype: nsjpegfiletype properties:nil; if (data) if (!_filemanager fileexistsatpath:_diskcachepath) _filemanager createdirectoryatpath:_diskcachepath withintermediatedirectories:yes attributes:nil error:null; _filemanag