System.InvalidCastException HResult=0x80004002 Message=无法投射 COM

Question

I am trying to read the sent items folder of my outlook, with the following code:

         Imports Microsoft.Office.Interop

        Imports Microsoft.Office.Interop.Outlook 
        Dim moApp As Outlook.Application

        Dim moNS As Outlook.NameSpace

        moApp = New Outlook.Application

        moNS = moApp.GetNamespace("MAPI")

        Dim oFolder As Outlook.MAPIFolder
        Dim oEmail As Outlook.MailItem

        oFolder = moNS.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderSentMail)

        For Each i As Object In oFolder.Items
            If TypeOf i Is MailItem Then
                MessageBox.Show("From: " & i.To)
            End If
        Next

Outlook folders

outlook folders

when I try to read the information of the MailItem object I get the error

"System.InvalidCastException
  HResult=0x80004002
  Message=Could not convert COM object of type 'System.__ComObject' to interface type 'Microsoft.Office.Interop.Outlook.MailItem'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{00063034-0000-0000-C000-0000000000000046}' failed due to the following error: No such interface is supported (0x80004002 (E_NOINTERFACE)).
  Source=SendMail"

But when I try it with the inbox folder, it works without any problem.

I am also validated to receive a MailItem object.

Has this error happened to anyone else?

Answer 1

Try to explore the problematic item in any low-level property explorer tool such as MFCMAPI or OutlookSpy. Is there any difference between other items in the folder? Is it a true mail item?

You may also try to use the late binding technology represented in.Net by reflection. The Type.InvokeMember allows to get property value without casting objects.

Note, you can use the "is" and "as" operators in C#. See How to: Programmatically Determine the Current Outlook Item for more information. If the is operator throws an exception you may try to use the as instead.

Also the Outlook object model provides the MessageClass property - a string representing the message class for the Outlook item. Under the hood the message class is used to identify what inspector to use in Outlook for displaying the item.