Question

I have written a base class from which I wish to derive several child classes (in this case Windows Form classes), and I’m using a Factory pattern in order to maintain a collection of the child instances, so that a form can only have one instance per primary key value (sort of a mash-up of Factory and Singleton patterns.)

I’m using the following code in the base form class:

Public Class PKSingletonForm
   Inherits Form

   Protected _PKValue As Int32 = 0
   Protected _strFormKey As String = ""
   Protected Shared _dictForms As New Dictionary(Of String, PKSingletonForm)

   Public Shared Function GetForm(Of T As {PKSingletonForm, New})(Optional ByVal PKValue As Int32 = 0) As T
      '** Create the key string based on form type and PK.
      Dim strFormKey As String = GetType(T).Name & "::" & PKValue.ToString

      '** If a valid instance of the form with that key doesn't exist in the collection, then create it.
      If (Not _dictForms.ContainsKey(strFormKey)) OrElse (_dictForms(strFormKey) Is Nothing) OrElse (_dictForms(strFormKey).IsDisposed) Then
         _dictForms(strFormKey) = New T()
         _dictForms(strFormKey)._PKValue = PKValue
         _dictForms(strFormKey)._strFormKey = strFormKey
      End If

      Return DirectCast(_dictForms(strFormKey), T)
   End Function
End Class

The idea is to create a child form (called UserInfoForm, for example) that inherits from the base form, and create an instance of it for user #42 as follows:

Dim formCurrentUser = PKSingletonForm.GetForm(of UserInfoForm)(42)

All this works as intended.

However, the UserInfoForm now has some properties I wish to set, and I would like to set them using Object Initializers, as opposed to after the form is created by the factory, like so:

Dim formCurrentUser As New UserInfoForm With { .ShowDeleteButton = False, .ShowRoleTabs = False }

Is there any way to combine these two methods, so I’ve got the factory as well as the initializer?

I’m not looking for:

Dim formCurrentUser = PKSingletonForm.GetForm(of UserInfoForm)(42)
formCurrentUser.ShowDeleteButton = False
formCurrentUser.ShowRoleTabs = False

…because the base class also has a ShowForm() method that takes additional base form parameters, wraps the GetForm() function, and shows the form.

Answer 1

Our ShowForm() method was written as follows:

Public Shared Sub ShowForm(Of T As {BaseForm, New})(Optional ByVal PKValue As Int32 = 0, <Several Parameters Here>)

   Dim formShown As BaseForm = GetForm(Of T)(PKValue, isRepeatable)

   <Do Stuff with Parameters Here>

   formShown.Show()
   formShown.BringToFront()
End Sub

Our solution was to take out the Shared (and the Generics), to simplify ShowForm() to:

Public Sub ShowForm(<Several Parameters Here>)

   <Do Stuff with Parameters Here>

   Me.Show()
   Me.BringToFront()
End Sub

That way, we can write:

Dim formCurrentUser = PKSingletonForm.GetForm(of UserInfoForm)(42)
formCurrentUser.ShowDeleteButton = False
formCurrentUser.ShowRoleTabs = False
formCurrentUser.ShowForm(blah, blah)

…as well as:

Dim formCurrentUser = PKSingletonForm.GetForm(of UserInfoForm)(42).ShowForm()