MFMailComposeViewController：解雇后与UITextField和UIAlertController有关的问题

Question

在我的应用程序中使用MFMailComposeViewControlle r之后我遇到两个问题：

1. 解除MFMailComposeViewController后，我的初始UITextField上的ViewController文字已清除
2. 尝试显示UIAlertController以表示MFMailComposeResult时，无法显示日志中的错误。

问题1：这是我的MFMailComposeViewController代码。这是UIAlertController（UIAlertControllerStyleActionSheet）的操作。

    UIAlertAction *email = [UIAlertAction
                        actionWithTitle:@"Email the link"
                        style:UIAlertActionStyleDefault
                        handler:^(UIAlertAction * action)
                        {

                            // composes new mail message with link
                            NSString *messageBody = self.link.text;

                            MFMailComposeViewController *mc = [[MFMailComposeViewController alloc] init];
                            mc.mailComposeDelegate = self;
                            [mc setMessageBody:messageBody isHTML:NO];


                            // customises UI to match application
                            [[mc navigationBar] setTintColor:[UIColor whiteColor]];
                            [self presentViewController:mc animated:YES completion:^{
                                [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];
                                [self setNeedsStatusBarAppearanceUpdate];
                            }];

                            [view dismissViewControllerAnimated:YES completion:nil];

                        }];

问题2：这是我为每个相关UIAlertController显示相应MFMailComposeResult的代码。

- (void) mailComposeController:(MFMailComposeViewController *)controller didFinishWithResult:(MFMailComposeResult)result error:(NSError *)error
{
    switch (result)
    {
        case MFMailComposeResultCancelled:{

            UIAlertController *alert=   [UIAlertController
                                         alertControllerWithTitle:@"SearchMe"
                                         message:@"The composition of this email has been cancelled."
                                         preferredStyle:UIAlertControllerStyleAlert];

            UIAlertAction *done = [UIAlertAction
                                   actionWithTitle:@"Done"
                                   style:UIAlertActionStyleDefault
                                   handler:^(UIAlertAction * action)
                                   {
                                       [alert dismissViewControllerAnimated:YES completion:nil];

                                   }];


            [alert addAction:done];
            [self presentViewController:alert animated:YES completion:nil];

            [alert dismissViewControllerAnimated:YES completion:nil];


    }

            break;
        case MFMailComposeResultSaved:{

            UIAlertController *alert=   [UIAlertController
                                         alertControllerWithTitle:@"SearchMe"
                                         message:@"The composition of this email has saved as a draft."
                                         preferredStyle:UIAlertControllerStyleAlert];

            UIAlertAction *done = [UIAlertAction
                                   actionWithTitle:@"Done"
                                   style:UIAlertActionStyleDefault
                                   handler:^(UIAlertAction * action)
                                   {
                                       [alert dismissViewControllerAnimated:YES completion:nil];

                                   }];


            [alert addAction:done];
            [self presentViewController:alert animated:YES completion:nil];

            [alert dismissViewControllerAnimated:YES completion:nil];


        }

            break;
        case MFMailComposeResultSent:{

            UIAlertController *alert=   [UIAlertController
                                         alertControllerWithTitle:@"SearchMe"
                                         message:@"The composition of this email has been sent."
                                         preferredStyle:UIAlertControllerStyleAlert];

            UIAlertAction *done = [UIAlertAction
                                   actionWithTitle:@"Done"
                                   style:UIAlertActionStyleDefault
                                   handler:^(UIAlertAction * action)
                                   {
                                       [alert dismissViewControllerAnimated:YES completion:nil];

                                   }];


            [alert addAction:done];
            [self presentViewController:alert animated:YES completion:nil];

            [alert dismissViewControllerAnimated:YES completion:nil];

        }


            break;
        case MFMailComposeResultFailed:
        {

            UIAlertController *alert=   [UIAlertController
                                         alertControllerWithTitle:@"SearchMe"
                                         message:@"The composition of this email has failed. Please try again."
                                         preferredStyle:UIAlertControllerStyleAlert];

            UIAlertAction *done = [UIAlertAction
                                   actionWithTitle:@"Done"
                                   style:UIAlertActionStyleDefault
                                   handler:^(UIAlertAction * action)
                                   {
                                       [alert dismissViewControllerAnimated:YES completion:nil];

                                   }];


            [alert addAction:done];
            [self presentViewController:alert animated:YES completion:nil];

            [alert dismissViewControllerAnimated:YES completion:nil];
        }



            break;
        default:
            break;
    }

    [self dismissViewControllerAnimated:YES completion:NULL];
}

日志中给出的错误是：

Warning: Attempt to present <UIAlertController: 0x14ed58b90> on <ViewController: 0x14ee1f7f0> whose view is not in the window hierarchy!