Modules, classes & object lifetime

Choose a home for behavior#

Moving code into a module does not automatically make it reusable. Remove accidental dependencies on particular Form controls and pass the values the operation needs.

A complete stateful class#

The project declares Counter.cls as a class module. Each New Counter gets its own mValue. The read-only property exposes a result without letting callers assign the field directly.

Option Explicit

Private mValue As Long

Public Property Get Value() As Long
    Value = mValue
End Property

Public Sub Add(ByVal amount As Long)
    mValue = mValue + amount
End Sub

Create a reference before using it#

Public Sub TryCounter()
    Dim counter As Counter
    Set counter = New Counter
    counter.Add 3
    counter.Add 2
    Debug.Print counter.Value
End Sub

The output is 5. Dim declares the reference; New creates an instance; Set assigns that reference. Use Nothing for an empty reference and Is to compare identity. Assign ordinary values with =.

A variable is not an ownership policy#

A reference remaining in a variable does not guarantee that its window or service is still usable. A closed Form is not automatically a fresh Form. A database connection needs an explicit close path. A component’s work must stop when its owning lifetime ends.

Use Form lifetime for windows and SDK lifecycle for components. Avoid an indefinitely retained global reference just to keep a temporary window reachable.

Test two instances#

Create two Counter instances, add to one and verify the other stays at zero. Apply the same test to a reusable visual component. The CustomerCard consumer exercises the package boundary instead of compiling the authoring source into the consuming app.