//假設這是一個網絡獲取的URL
NSString?*path?=?@"http://pic.rpgsky.net/images/2016/07/26/3508cde5f0d29243c7d2ecbd6b9a30f1.png";
NSData?*data?=?[NSData?dataWithContentsOfURL:[NSURL?URLWithString:path]];
//調用獲取圖片擴展名
NSString?*string?=?[self?contentTypeForImageData:data];
//輸出結果為?png
NSLog(@"%@",string);
