How to detect if user select cancel InputBox VBA Excel

Question

I have an input box asking user to enter a date. How do I let the program know to stop if the user click cancel or close the input dialog instead of press okay.

Some

Answer 1

Following example uses InputBox method to validate user entry to unhide sheets: Important thing here is to use wrap InputBox variable inside StrPtr so it could be compared to '0' when user chose to click 'x' icon on the InputBox.

Sub unhidesheet()

Dim ws As Worksheet
Dim pw As String

pw = InputBox("Enter Password to Unhide Sheets:", "Unhide Data Sheets")
If StrPtr(pw) = 0 Then

   Exit Sub
ElseIf pw = NullString Then
   Exit Sub
ElseIf pw = 123456 Then
    For Each ws In ThisWorkbook.Worksheets
        ws.Visible = xlSheetVisible
    Next
End If
End Sub

Answer 2

The solution above does not work in all InputBox-Cancel cases. Most notably, it does not work if you have to InputBox a Range.

For example, try the following InputBox for defining a custom range ('sRange', type:=8, requires Set + Application.InputBox) and you will get an error upon pressing Cancel:

Sub Cancel_Handler_WRONG()
Set sRange = Application.InputBox("Input custom range", _
    "Cancel-press test", Selection.Address, Type:=8)
If StrPtr(sRange) = 0 Then  'I also tried with sRange.address and vbNullString
    MsgBox ("Cancel pressed!")
    Exit Sub
End If
    MsgBox ("Your custom range is " & sRange.Address)
End Sub

The only thing that works, in this case, is an "On Error GoTo ErrorHandler" statement before the InputBox + ErrorHandler at the end:

Sub Cancel_Handler_OK()
On Error GoTo ErrorHandler
Set sRange = Application.InputBox("Input custom range", _
    "Cancel-press test", Selection.Address, Type:=8)
MsgBox ("Your custom range is " & sRange.Address)
Exit Sub
ErrorHandler:
    MsgBox ("Cancel pressed")
End Sub

So, the question is how to detect either an error or StrPtr()=0 with an If statement?

Answer 3

If the user clicks Cancel, a zero-length string is returned. You can't differentiate this from entering an empty string. You can however make your own custom InputBox class...

EDIT to properly differentiate between empty string and cancel, according to this answer.

Your example

Private Sub test()
    Dim result As String
    result = InputBox("Enter Date MM/DD/YYY", "Date Confirmation", Now)
    If StrPtr(result) = 0 Then
        MsgBox ("User canceled!")
    ElseIf result = vbNullString Then
        MsgBox ("User didn't enter anything!")
    Else
        MsgBox ("User entered " & result)
    End If
End Sub

Would tell the user they canceled when they delete the default string, or they click cancel.

See http://msdn.microsoft.com/en-us/library/6z0ak68w(v=vs.90).aspx