How to check for existing parent?-CodePudding

In general, I've been looking for how to properly check that an object is assigned.
In this particular case, it is the parent property.
I have forms that sometimes have a parent, and have slightly different behavior on resizing.

But this code

If (Not Parent Is Nothing) Then
   MsgBox "Is Nothing says Parent is Assigned"
Else
   MsgBox "Is Nothing says Parent is not  Assigned"
End If

If (IsObject(Parent)) Then
   MsgBox "IsObject says Parent is Assigned"
Else
   MsgBox "IsObject says Parent is not  Assigned"
End If

both work fine if there is a parent and both give an error if not.

Run-time error '2452' The expression you entered has an invalid reference to the Parent property.

Is the only hope to catch the error and handle it there?

CodePudding user response：

You can check, if the form is opened as a main form:

If IsFormOpen(Me.Name) Then
   MsgBox Me.Name & " has no parent."
Else
   MsgBox Me.Name & " has a parent."
End If

' Checks if a form by name is open in the current database.
' Returns True if it does, False if not.
'
' 2011-10-10, Cactus Data ApS, Gustav Brock
'
Public Function IsFormOpen(ByVal FormName As String) As Boolean

    Dim Form    As Form
    
    For Each Form In Forms
        If Form.Name = FormName Then
            Exit For
        End If
    Next
    
    IsFormOpen = Not Form Is Nothing

End Function

CodePudding user response：

If you know the name of form(s) that form could be installed on as subform, can either loop through Forms collection and test if one equals "parent" form name (see @Gustav answer) or use IsLoaded method to test if a specific form is open in Forms collection (If CurrentProject.AllForms("DataBituminous").IsLoaded Then). Form when used as subform will not be in Forms collection.

If you don't want to hard-code parent form name, then use error handling code to deal with missing parent. Example found at https://www.access-programmers.co.uk/forums/threads/how-to-check-if-a-form-has-a-parent-form.157642/

Private Property Get HasParent As Boolean
On error GoTo handler
  HasParent = Typename(Me.Parent.Name) = "String"
  Exit Property
handler:
End Property