MVPアプローチを使用して、コントロールが動的であるユーザーフォーム入力を検証します

Your model class being named *Form got me confused for a minute; I might have named the form like that (or TestView) and used TestModel for the model class :)

If the role of the view/form is to present the data, the role of the model is to, well, be the data. TestProduct is one such piece of data: its validity is also presentable data. You could consider this metadata and go wild and have a some TestModelValidator class implementing some IModelValidator interface that might look like this:

Public Function IsValid() As Boolean
End Function

...but that's probably overkill. If we're good with having the model responsible for both the data and its validation, then the model class could look like this:

Option Explicit
Private Type TState
    ValidationErrors As Collection
    ProductName As String
    '...other state members
End Type
Private this As TState

Private Sub Class_Initialize()
    Set this.ValidationErrors = New Collection
End Sub

Public Property Get ProductName() As String
    ProductName = this.ProductName
End Property

Public Property Let ProductName(ByVal value As String)
    this.ProductName = value
End Property

'...other model properties...

Public Property Get IsValid() As Boolean

    Dim validProductName As Boolean
    validProductName = Len(this.ProductName) <> 0
    this.ValidationErrors.Remove "ProductName" '<~ NOTE air code, verify this works
    If Not validProductName Then this.ValidationErrors("ProductName") = "Product name cannot be empty"
    '...validation logic for other properties...

    IsValid = validProductName
End Property

Public Property Get ValidationErrors() As String
    ReDim result(0 To this.ValidationErrors.Count)
    Dim e As Variant, i As Long
    For Each e In this.ValidationErrors
        result(i) = e
        i = i + 1
    Next
    ValidationErrors = Join(vbNewLine, result)
End Property

Now the view can manipulate the model - not what's happening here:

Private Sub CommandButton1_Click()

With Me
    If .CheckBox1.Value = True Then
        DataEntryForm.TestProduct = .CheckBox1.Caption
    ElseIf .CheckBox2.Value = True Then
        DataEntryForm.TestProduct = .CheckBox2.Caption

Instead of querying the UI, listen in when the UI tells you what's going on - handle each control's Change event, and then let the model drive the state of the UI:

Private Sub CheckBox1_Change()
    If Me.CheckBox1.Value Then
        Model.ProductName = Me.CheckBox1.Caption
        Validate
    End If
End Sub

Private Sub CheckBox2_Change()
    If Me.CheckBox2.Value Then
        Model.ProductName = Me.CheckBox2.Caption
        Validate
    End If
End Sub

Private Sub CodeBox_Change()
    Model.Code = CodeBox.Text
    Validate
End Sub

Private Sub DescriptionBox_Change()
    Model.Description = DescriptionBox.Text
    Validate
End Sub

Private Sub Validate()
    Dim valid As Boolean
    valid = Model.IsValid

    Me.OkButton.Enabled = valid
    Me.ValidationErrorsLabel.Caption = Model.ValidationErrors
    Me.ValidationErrorsLabel.Visible = Not valid
End Sub

Hope it helps!

編集/補遺：モデルの状態を使用して、そのようなコントロールを表示するかどうかも決定します。モデルクラスは、可能な限り多くのロジックをカプセル化する必要があります（フォームのコードビハインドに含めるのとは異なります）。これにより、すべてのエッジケースを手動でテストしなくても、モデルクラスに対してその動作を検証および文書化するテストを簡単に作成できます。何かを壊す可能性のある変更を加えるたびに、実際の形で！言い換えると、コンボボックスにデータを入力したり、チェックボックスコントロールをできるだけ多く作成したりするために、ビュー/フォームにサプライヤ名のコレクションが必要な場合、このデータをカプセル化するのはモデルの仕事です。

つまり、モデルロジックの一部を駆動するためにフラグが必要な場合は、そのフラグをモデルの状態の一部にします。

Private Type TState
    '...
    ProductTypes As Collection
End Type

Public Property Get HasProductTypes() As Boolean
    HasProductTypes = this.ProductTypes.Count > 0
End Property

Public Property Get ProductTypes() As Variant
    Dim result(0 To ProductTypes.Count)
    Dim pt As Variant, i As Long
    For Each pt In this.ProductTypes
        result(i) = pt
        i = i + 1
    Next
    ProductTypes = result
End Property

Public Property Get IsValid() As Boolean

    Dim validProductName As Boolean
    validProductName = Len(this.ProductName) <> 0
    this.ValidationErrors.Remove "ProductName" '<~ NOTE air code, verify this works
    If Not validProductName Then this.ValidationErrors("ProductName") = "Product name cannot be empty"
    '...validation logic for other properties...

    Dim validProductType As Boolean '<~ model is valid with an empty ProductType if there are no product types
    validProductType = IIf(HasProductTypes, Len(this.ProductType) > 0, True)

    IsValid = validProductName And validProductType
End Property