为什么MailController不显示To和Body文本？

Question

我在Objective-C上有这段代码：

- (IBAction)Mail:(id)sender {
    NSString *MailTitle = @"Mi Opinion About this App";
    NSString *MailBody = @"Hi, I am an user of this app and I think that ";
    NSArray *MailTo = [NSArray arrayWithObject:@"contact@domain.com"];

    MFMailComposeViewController *MailController = [[MFMailComposeViewController alloc] init];
    MailController.mailComposeDelegate = self;
    [MailController setSubject:MailTitle];
    [MailController setMessageBody:MailBody isHTML:NO];
    [MailController setToRecipients:MailTo];
    [self presentViewController:MailController animated:YES completion:NULL];
}

它正确显示主题，但字段＆＃34; To＆＃34;和＆＃34; Body＆＃34;在iOS模拟器中是空的！