从SKScene打开MFMailComposeViewController的方法如下：

-(void)sendmail {

if ([MFMailComposeViewController canSendMail]) {

    MFMailComposeViewController *mailer = [[MFMailComposeViewController alloc] init];
    mailer.delegate = self;
    NSArray *recipients = [NSArray arrayWithObjects:@"nothing@gmail.com", nil];
    [mailer setToRecipients:recipients];

    UIViewController *vc = self.view.window.rootViewController;
    [vc presentViewController:mailer animated:YES completion:nil];
 }
}

这是可行的，但是当我想返回到SKScene时，委托方法没有被调用，无法返回。
这是SKScene的.h：

@interface SettingScene : SKScene <UINavigationControllerDelegate, MFMailComposeViewControllerDelegate>

怎么了？
谢谢