Question

Lets say I have a custom collection and a custom object that have a Parent-Child relationship

I have a userform where the user names the collection and provides input for other properties of the collection. When they click “Add Parent” the click event is handled and calls the following function:

Public Function AddParent()

    Dim newParent As clsParent

    Set newParent = New clsParent

    'Add Parent Properties'

        With frmAddParent
            newParent.Name = .cboParentName.Value
            newParent.Width = .txtParentWidth.Value
            newParent.Xslope = .txtParentCrossSlope.Value
        End With

    'show the form for creating the Child Object'

    frmAddLaneMaterial.Show

End Function

The user then sees a new form for creating a Child object. When the user clicks “Add Child” the event is handled and calls the following function:

Public Function AddChild()

    Dim newChild As clsChild
    Set newChild = New clsChild

        'Add child Properties'

        With frmAddChild

            newChild.Name = .cboParentName.Value
            newChild.LayerNumber = .cboLayerNum.Value
            newChild.xSlope = newParent.Xslope

        End With

    'Add the new child to the parent collection'

    newParent.Add newChild

End Function 

And then the user needs to be able to return to the userform and add another child.

The lines that won’t work are:

            newChild.xSlope = newParent.Xslope

and:

newParent.Add newChild

I get an ‘object required’ error.

How do I/where do I add the child to the Parent Collection?

Answer 1

First of all, newParent is local to the AddParent function so AddChild has no visibility of it. To fix that, you would need to move Dim newParent As clsParent out of the AddParent function and make it a module-level variable. This assumes that AddParent and AddChild are in the same module.

Secondly, newParent.Add newChild will only work if you have written an Add method in clsParent. If you have not then you’ll need to write one. I have no idea how you plan on using it, but the following code is pretty generic and should get you pointed in the right direction. This code would go in the clsParent module:

Private m_oChildren As Collection

Sub Add(Child As clsChild)
    If m_oChildren Is Nothing Then Set m_oChildren = New Collection
    m_oChildren.Add Child
End Sub

This would build a private collection of clsChild objects that you would manipulate using additional methods or expose via Property Get.

UPDATE: To address your comment, if you want to keep multiple parents you’ll need to add a collection for that. For example:

Dim Parents As Collection

Public Function AddParent()
Dim newParent As clsParent
    Set newParent = New clsParent

    'Add Parent Properties'
    With frmAddParent
        newParent.Name = .cboParentName.Value
        newParent.Width = .txtParentWidth.Value
        newParent.Xslope = .txtParentCrossSlope.Value
    End With

    'Initialize the collection of Parents if it has not already been done'
    If Parents Is Nothing Then Set Parents = New Collection
    'Add the new parent object to the Parents collection'
    Parents.Add newParent

    'show the form for creating the Child Object'
    frmAddLaneMaterial.Show
End Function


Public Function AddChild()
Dim newChild As clsChild
    Set newChild = New clsChild

    'Add child Properties'
    With frmAddChild
        newChild.Name = .cboParentName.Value
        newChild.LayerNumber = .cboLayerNum.Value
        newChild.xSlope = newParent.Xslope
    End With

    'Add the new child to the most recently added parent in the parent collection'
    Parents.Item(Parents.Count).Add newChild

End Function

Of course, now you have another collection to keep track of. It gets really tricky keeping track of multiple instances of forms (which I assume is what you are doing) and it is easy to suddenly find yourself with an unmanageable mess.