UIActionSHeet を使用して、複数の共有オプション (Facebook、Twitter、メール) から選択しています
しかし、オプションを選択すると、この警告が表示されます
 Warning: Attempt to dismiss from view controller <UINavigationController: 0x1ed7eaf0> while a presentation or dismiss is in progress 
これは私が使用するコードです:
- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{
    //BOOL displayedNativeDialog;
    SLComposeViewController * tw =  [SLComposeViewController composeViewControllerForServiceType:SLServiceTypeTwitter];
    //TWTweetComposeViewController * tw = [[TWTweetComposeViewController alloc]init];
    tw.completionHandler = ^(TWTweetComposeViewControllerResult result)
    {
        [self dismissViewControllerAnimated:YES completion:nil];
    };
    SLComposeViewController * fb = [SLComposeViewController composeViewControllerForServiceType:SLServiceTypeFacebook];
    fb.completionHandler = ^(SLComposeViewControllerResult result)
    {
        [self dismissViewControllerAnimated:YES completion:nil];
    };
    MFMailComposeViewController * mail = [[MFMailComposeViewController alloc]init];
    [mail setMailComposeDelegate:self];
    [mail.navigationBar setBackgroundColor:[UIColor blackColor]];
    NSData * imageData = [NSData dataWithData:UIImagePNGRepresentation(previewImageView.image)];
    switch (buttonIndex) {
        case 0:
            UIImageWriteToSavedPhotosAlbum(previewImageView.image, nil, nil, nil);
            break;
        case 1:
            [fb addImage:previewImageView.image];
            [self presentViewController:fb animated:YES completion:nil];
            fb = nil;       
            break;
        case 2:
            [actionSheet dismissWithClickedButtonIndex:-1 animated:YES];
            [tw addImage:previewImageView.image];
            [self presentViewController:tw animated:YES completion:nil];
            break;
        case 3:
            [mail addAttachmentData:imageData mimeType:@"image/png" fileName:@"Image.png"];
            [self presentViewController:mail animated:YES completion:nil];
            break;
        default:
            break;
    }
}
また、デリゲート関数を使用してみました:
- (void)actionSheet:(UIActionSheet *)actionSheet didDismissWithButtonIndex:(NSInteger)buttonIndex
しかし、私は同じ警告を受けました。