enumerateByteRangesUsingBlock:方法在NSData类中，在Apple文档中解释如下:Enumeratethrougheachrangeofbytesinthedataobjectusingablock.-(void)enumerateByteRangesUsingBlock:(void(^)(constvoid*bytes,NSRangebyteRange,BOOL*stop))blockParametersblockTheblocktoapplytobyterangesinthearray.Theblocktakesthreearguments:bytes