无法设置MFMessageComposeViewController的收件人？

I have a method like this:

我有这样的方法:

void sendSMS{

        if ([MFMessageComposeViewController canSendText]) {

            MFMessageComposeViewController *picker = [[MFMessageComposeViewController alloc] init];

            picker.recipients = [NSArray arrayWithObject:@"0933660805"];
            [picker  setBody:@"Message body"];
            picker.messageComposeDelegate = self;

            [self.navigationController  presentModalViewController:picker animated:YES];
            //[picker release];

            return;

        }

    }
void se