VBA如何：在Outlook中的ActiveInspector.CurrentItem为null时提示？

Question

If this has been posted, please let me know as I wasn't able to find it :)

I've made a prompt in Outlook that selects the current mail item and deletes it before opening an application:

Dim objApp As Outlook.Application
    Set objApp = Application
On Error Resume Next
Select Case TypeName(objApp.ActiveWindow)
    Case "Explorer"
        Set CurrentItem = objApp.ActiveExplorer.Selection.item(1)
    Case "Inspector"
        Set CurrentItem = objApp.ActiveInspector.CurrentItem
End Select

Dim mailItem As Outlook.mailItem
Set mailItem = CurrentItem

Dim deleteItem As Boolean
    deleteItem = objApp.mailItem.Delete

If MsgBox("Would you like to move this message to deleted items?", vbYesNo + vbQuestion, "File Indexing") _
        = vbYes Then
            mailItem = deleteItem
            deleteItem = True
        Else
            deleteItem = False
End If

All of that works perfectly, but I would like a modal window to appear if there is no current item selected , but I'm not sure how to add that in. Would it be within the same IfThen, or a completely different statement? I've tried adding something along the lines of

If CurrentItem = Null Then
MsgBox ("Please select a mail item")
End If

but then the MsgBox never appears and the code executes normally. Thank you for any help!

EDIT: Thanks for the responses. Unfortunately I found a couple of errors unrelated to this so I need to address them before I add additional code to my Outlook button.

Answer 1

Try this

Option Explicit

Private Sub test()

Dim currentItem As Object

Dim objApp As Outlook.Application

Set objApp = Application

On Error Resume Next

Select Case TypeName(objApp.ActiveWindow)
    Case "Explorer"
        Set currentItem = objApp.ActiveExplorer.Selection.Item(1)
    Case "Inspector"
        Set currentItem = objApp.ActiveInspector.currentItem
End Select

On Error GoTo 0

If currentItem Is Nothing Then

    MsgBox ("Please select a mail item")

End If

End Sub

Answer 2

See VBA Check if variable is empty .

Where do you run the code listed above? Is it the NewInspector event handler?

objApp.ActiveExplorer.Selection.item(1)

Anyway, I'd suggest breaking the chain of property and method calls and declaring them on separate line of code. So, you will find what property or method fails or returns null.

Try to use the following code:

  If Not CurrentItem Is Nothing Then
    ' obj initialized. '
  Else
    MsgBox ("Please select a mail item")
  End If

Answer 3

Thanks for the help, but my boss was able to come up with this little tid-bit that seems to be working properly:

Select Case TypeName(objApp.ActiveWindow)
    Case "Explorer"
        If objApp.ActiveExplorer.Selection.Count > 0 Then
            Set currentItem = objApp.ActiveExplorer.Selection.Item(1)
        Else
            MsgBox ("No Messages Selected.")
            Exit Sub
        End If
    Case "Inspector"
        Set currentItem = objApp.ActiveInspector.currentItem
    Case Else
        MsgBox ("Please select a mail item.")
        Exit Sub