VBA Creating a Custom Class Class module scope, instancing and re-use
Example
By default, a new class module is a Private class, so it is only available for instantiation and use within the VBProject in which it is defined. You can declare, instantiate and use the class anywhere in the same project:
'Class List has Instancing set to Private
'In any other module in the SAME project, you can use:
Dim items As List
Set items = New List
But often you'll write classes that you'd like to use in other projects without copying the module between projects. If you define a class called List in ProjectA, and want to use that class in ProjectB, then you'll need to perform 4 actions:
-
Change the instancing property of the
Listclass inProjectAin the Properties window, fromPrivatetoPublicNotCreatable -
Create a public "factory" function in
ProjectAthat creates and returns an instance of aListclass. Typically the factory function would include arguments for the initialization of the class instance. The factory function is required because the class can be used byProjectBbutProjectBcannot directly create an instance ofProjectA's class.Public Function CreateList(ParamArray values() As Variant) As List Dim tempList As List Dim itemCounter As Long Set tempList = New List For itemCounter = LBound(values) to UBound(values) tempList.Add values(itemCounter) Next itemCounter Set CreateList = tempList End Function -
In
ProjectBadd a reference toProjectAusing theTools..References...menu. -
In
ProjectB, declare a variable and assign it an instance ofListusing the factory function fromProjectADim items As ProjectA.List Set items = ProjectA.CreateList("foo","bar") 'Use the items list methods and properties items.Add "fizz" Debug.Print items.ToString() 'Destroy the items object Set items = Nothing
