How to use a single VBA procedure to read or write both custom and built-in Document Properties

Article contributed by Astrid Zeelenberg

When you work with Document Properties in code, most people end up with two functions or subroutines, one to write built-in Document Properties and one for custom Document Properties; because in each case the object used to refer to the Document Properties is different – you have to use the CustomDocumentProperties and BuiltinDocumentProperties collection as appropriate. But this can be very inconvenient.

Writing Document Properties

However, you can write a procedure which checks whether the property you want to write the value for is custom or built-in, and then uses the appropriate collection. (Note: If you are not familiar with calling subroutines with arguments, see: How to cut out repetition and write much less code, by using subroutines and functions that take arguments).

This is how to do it:

Public Sub WriteProp(sPropName As String, sValue As String, _
      Optional lType As Long = msoPropertyTypeString)

'In the above declaration, "Optional lType As Long = msoPropertyTypeString" means
'that if the Document Property's Type is Text, we don't need to include the lType argument
'when we call the procedure; but if it's any other Prpperty Type (e.g. date) then we do

Dim
bCustom As Boolean

  On Error GoTo ErrHandlerWriteProp

  'Try to write the value sValue to the custom documentproperties
  'If the customdocumentproperty does not exists, an error will occur
  'and the code in the errorhandler will run
  ActiveDocument.BuiltInDocumentProperties(sPropName).Value = sValue
  'Quit this routine
  Exit Sub

Proceed:
  'We know now that the property is not a builtin documentproperty,
  'but a custom documentproperty, so bCustom = True
  bCustom = True

Custom:
  'Try to set the value for the customproperty sPropName to sValue
  'An error will occur if the documentproperty doesn't exist yet
  'and the code in the errorhandler will take over
  ActiveDocument.CustomDocumentProperties(sPropName).Value = sValue
  Exit Sub

AddProp:
  'We came here from the errorhandler, so know we know that
  'property sPropName is not a built-in property and that there's
  'no custom property with this name
  'Add it

  On Error Resume Next
  ActiveDocument.CustomDocumentProperties.Add Name:=sPropName, _
    LinkToContent:=False, Type:=lType, Value:=sValue

  If Err Then
    'If we still get an error, the value isn't valid for the Property Type
    'e,g an invalid date was used
    Debug.Print "The Property " & Chr(34) & _
     sPropName & Chr(34) & " couldn't be written, because " & _
     Chr(34) & sValue & Chr(34) & _
     " is not a valid value for the property type"
  End If

  Exit Sub

ErrHandlerWriteProp:
  Select Case Err
    Case Else
   'Clear the error
   Err.Clear
   'bCustom is a boolean variable, if the code jumps to this
   'errorhandler for the first time, the value for bCustom is False
   If Not bCustom Then
     'Continue with the code after the label Proceed
     Resume Proceed
   Else
     'The errorhandler was executed before because the value for
     'the variable bCustom is True, therefor we know that the
     'customdocumentproperty did not exist yet, jump to AddProp,
     'where the property will be made
     Resume AddProp
   End If
  End Select

End Sub


We could call the above procedure like this:

Sub Test()
  'Author is a built-in property
  Call WriteProp(sPropName:="Author", sValue:="William Shakespeare")

  'Date Updated is a custom document property
  Call WriteProp(sPropName:="Date Updated", sValue:="11 Mar 2001", _
    lType:=msoPropertyTypeDate)
End Sub


Reading Document Properties

The same principle can be used when reading Document Properties:

Function ReadProp(sPropName As String) As Variant

Dim bCustom As Boolean
Dim sValue As String

  On Error GoTo ErrHandlerReadProp
  'Try the built-in properties first
  'An error will occur if the property doesn't exist

  sValue = ActiveDocument.BuiltInDocumentProperties(sPropName).Value
  ReadProp = sValue
  Exit Function

ContinueCustom:
  bCustom = True

Custom:
  sValue = ActiveDocument.CustomDocumentProperties(sPropName).Value
  ReadProp = sValue
  Exit Function

ErrHandlerReadProp:
  Err.Clear
  'The boolean bCustom has the value False, if this is the first
  'time that the errorhandler is runned
  If Not bCustom Then
    'Continue to see if the property is a custom documentproperty
    Resume ContinueCustom
  Else
    'The property wasn't found, return an empty string
    ReadProp = ""
    Exit Function
  End If

End Function


We could call the function like this:

Sub Test()

Dim PropVal As String
 
  PropVal = ReadProp("Author")
  Debug.Print PropVal

  PropVal = ReadProp("Date Completed")
  Debug.Print PropVal

End Sub


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