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A data object containing the JPEG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.

UIKIT_EXTERN  NSData * __nullable UIImagePNGRepresentation(UIImage * __nonnull image);                               // return image as PNG. May return nil if image has no CGImageRef or invalid bitmap formatUIKIT_EXTERN  NSData * __nullable UIImageJPEGRepresentation(UIImage * __nonnull image, CGFloat compressionQuality);  // return image as JPEG. May return nil if image has no CGImageRef or invalid bitmap format. compression is 0(most)..1(least)

项目中自定义的用来保存UIImage+(void)saveImageToDomainsWithDirectorystringByAppendingPathComponent:(NSString *)suffix WithImage:(UIImage *)image{    //JEPG格式    //压缩图片     NSData *imagedata=UIImageJPEGRepresentation(image,1.0);    //获取沙盒路径    NSArray*paths=NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES);    //获取documents路径    NSString *documentsDirectory=[paths objectAtIndex:0];    //添加文件名及后缀    NSString *savedImagePath=[documentsDirectory stringByAppendingPathComponent:suffix];    //写入文件    [imagedata writeToFile:savedImagePath atomically:YES];}//取图片+ (UIImage *)fetchImageWithDirectorystringByAppendingPathComponent:(NSString *)suffix{NSString *aPath3=[NSString stringWithFormat:@"%@/Documents/%@.png",NSHomeDirectory(),suffix];UIImage *imgFromUrl3=[[UIImage alloc]initWithContentsOfFile:aPath3];UIImageView* imageView3=[[UIImageView alloc]initWithImage:imgFromUrl3];    return imageView3.image;}