Microsoft Access: Check if Form Object is a Subform

How do you check if the form object is a subform in Access without triggering a runtime error? Hint: this is a trick question.

Microsoft Access: Check if Form Object is a Subform

As far as I am aware, there is no property on a form object that you can check to see whether it is either the topmost form or a subform.  

The form object does have a Parent property.  If the form is a subform, then it will have a parent object defined in that property.  If it is the topmost form, though, any reference to the property will raise error 2452:

The expression you entered has an invalid reference to the Parent property.

In fact, we can't even check to see if the property is nothing without raising the above error:

The simplest option, then, is to isolate the IsSubform check in a standalone function and ignore any errors the function may generate.

The Code: IsSubform()

'Returns True if the passed form object is a subform of a parent form
Function IsSubform(Frm As Form) As Boolean
    On Error Resume Next
    IsSubform = (Not Frm.Parent Is Nothing)
End Function

Image by Andreas Wohlfahrt from Pixabay

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