Objective-C Post请求不发送数据

Question

我正在尝试将帖子请求发送到网址

但服务器始终获取空数据

NSString *post = [NSString stringWithFormat:@"cmd=login&account=%@&password=%@" ,account ,password];
NSData *data = [post dataUsingEncoding:NSASCIIStringEncoding];
NSMutableData *postData = [data mutableCopy];

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];

[request setURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://myurl.com"]]];

[request setHTTPMethod:@"POST"];

[request setHTTPBody:postData];

NSError *error = nil;
NSHTTPURLResponse* urlResponse = nil;
NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:&urlResponse error:&error];
NSString *returnString = [[NSString alloc] initWithData:returnData encoding:NSASCIIStringEncoding];
NSLog(@"%@", returnString);
NSLog(@"error: %@", error.localizedFailureReason);

这是回复

2014-08-18 17：21：52.332 SignPos [2755：303] {“resp”：99，“desc”：“invalid cmd”}

2014-08-18 17：21：52.333 SignPos [2755：303]错误：（null）

有什么不对吗？

谢谢！