获取服务器文件的长度

 1 实现NSURLConnectionDataDelegate的代理方法
 2 - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
 3     NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
 4     
 5     if([httpResponse respondsToSelector:@selector(allHeaderFields)]){
 6         NSDictionary *fields = [httpResponse allHeaderFields];
 7         int totalSize = [[fields objectForKey:@"Content-Length"]             intValue];
 8     }
 9 }
10 
11 totalSize就是文件的长度