無法轉換類型為'System .__ ComObject'的COM對象

Question

當我在下面的代碼中進行強制轉換時，出現錯誤

代碼：

string subject = ((Microsoft.Office.Interop.Outlook.MailItem)myInbox.Items[temp])
    .Subject.ToString();

無法將類型為“ System .__ ComObject”的COM對象轉換為接口類型為“ Microsoft.Office.Interop.Outlook.MailItem”。 此操作失敗，因為具有以下錯誤的IID為“ {00063034-0000-0000-C000-000000000046}”的COM組件上的COM接口上的QueryInterface調用由於以下錯誤而失敗：不支持此類接口（HRESULT的異常：0x80004002（E_NOINTERFACE）） 。

Answer 1

您需要先檢查項目類型。 Outlook文件夾可能包含各種類型的項目：

Object selObject = this.Application.ActiveExplorer().Selection[1];
        if (selObject is Outlook.MailItem)
        {
            Outlook.MailItem mailItem =
                (selObject as Outlook.MailItem);
            itemMessage = "The item is an e-mail message." +
                " The subject is " + mailItem.Subject + ".";
            mailItem.Display(false);
        }
        else if (selObject is Outlook.ContactItem)
        {
            Outlook.ContactItem contactItem =
                (selObject as Outlook.ContactItem);
            itemMessage = "The item is a contact." +
                " The full name is " + contactItem.Subject + ".";
            contactItem.Display(false);
        }
        else if (selObject is Outlook.AppointmentItem)
        {
            Outlook.AppointmentItem apptItem =
                (selObject as Outlook.AppointmentItem);
            itemMessage = "The item is an appointment." +
                " The subject is " + apptItem.Subject + ".";
        }
        else if (selObject is Outlook.TaskItem)
        {
            Outlook.TaskItem taskItem =
                (selObject as Outlook.TaskItem);
            itemMessage = "The item is a task. The body is "
                + taskItem.Body + ".";
        }
        else if (selObject is Outlook.MeetingItem)
        {
            Outlook.MeetingItem meetingItem =
                (selObject as Outlook.MeetingItem);
            itemMessage = "The item is a meeting item. " +
                 "The subject is " + meetingItem.Subject + ".";
        }

有關更多信息，請參見如何：以編程方式確定當前Outlook項目 。

Answer 2

string subject = myInbox.Items[temp])
    .Subject.ToString();

無需先檢查myinbox對象是否具有subject屬性而不是string，然后如果它是string formate則需要對其進行鑄造，則無需進行鑄造。