Option Compare Database
Option Explicit

Public mcolFormInstances As New Collection

Public Function CheckForFormInstance(strFormName As String, Optional strFilter As String) As Form
On Error GoTo Err_Handler

    Dim i As Integer
    
    Set CheckForFormInstance = Form_Empty
    
    For i = 1 To mcolFormInstances.Count
        If mcolFormInstances(i).Name = strFormName Then
            If mcolFormInstances(i).Filter = strFilter Then
                Set CheckForFormInstance = mcolFormInstances(i)
                GoTo Code_Exit
            Else
                Select Case strFormName
                    Case "frmStudentList"
                        Set CheckForFormInstance = mcolFormInstances(i)
                        GoTo Code_Exit
                End Select
            End If
        End If
Next_Loop:
        If i = mcolFormInstances.Count Then
            Exit For
        End If
    Next i

Code_Exit:
    Exit Function

Err_Handler:
    If Err.Number = 2467 Then ' object is broken
        mcolFormInstances.Remove i
        i = i - 1
        GoTo Next_Loop
    End If
    DisplayUnexpectedError Err.Number, Err.Description
    Resume Code_Exit
    'Resume Next
End Function

Public Sub CloseFormInstance(frm As Form)
On Error GoTo Err_Handler
    
    mcolFormInstances.Remove CStr(frm.Hwnd)

Code_Exit:
    Set frm = Nothing
    Exit Sub
    
Err_Handler:
    If Err.Number = 5 Then ' the hWnd key doesn't exist in mcolFormInstances
        
        Resume Code_Exit
    End If
    DisplayUnexpectedError Err.Number, Err.Description
    Resume Code_Exit
    'Resume Next
End Sub

Public Function OpenFormInstance(strFormName As String, Optional strFilter As String) As Form
On Error GoTo Err_Handler
    
    Dim frm As Form
    Dim mdl As Module
    
    Set frm = CheckForFormInstance(strFormName, strFilter)
    
    If frm Is Form_Empty Then

' THIS IS THE PART - START

        Select Case strFormName
            Case "frmStudAgenda"
                Set frm = New Form_frmStudAgenda
            Case "frmStudentList"
                Set frm = New Form_frmStudentList
            Case "frmStudInfo"
                Set frm = New Form_frmStudInfo
            Case "frmStudRecords"
                Set frm = New Form_frmStudRecords
            Case "frmUnitInfo"
                Set frm = New Form_frmUnitInfo
            Case Else
                DoCmd.OpenForm strFormName, , , strFilter
                GoTo Code_Exit
        End Select

' THIS IS THE PART - END
        
        If strFilter <> "" Then
            frm.Filter = strFilter
            frm.FilterOn = True
        End If
        
        mcolFormInstances.Add Item:=frm, Key:=CStr(frm.Hwnd)
        
        frm.Visible = True
    Else
        frm.Visible = True
        frm.SetFocus
    End If

Code_Exit:
    Set OpenFormInstance = frm
    Set frm = Nothing
    Exit Function

Err_Handler:
    DisplayUnexpectedError Err.Number, Err.Description
    Resume Code_Exit
    'Resume Next
End Function