验证checkListBox？

Question

我有两个forms (1和2)。我一直在与一些代码做斗争，这些代码会阻止用户在checkedListBox中选择一个没有从前一个表单(form1)添加到ListBox2中的项。

我所拥有的代码有点奇怪，因为即使项目是从form1添加到form1中的，它仍然会继续显示msgBox。我需要msgBox只显示那些没有添加到listbox2，form1中的项目。

以下是我所拥有的：

Public Class Form1
    Dim ActSubject As Boolean
    Public Function ActivateSubject() As String
        Return ActSubject
    End Function

    Private Sub ListBox2_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox2.TextChanged
        Dim x As New Items
        x.AvailableItems = ListBox2.Items.ToString
        For Each x In ListBox2.Items
            If ListBox2.Items.Contains(x) Then
               ActSubject = True
            Else
               ActSubject = False
            End If
        Next
    End Sub
End Class

Public Class Form2
    Dim HaveActSubject As Boolean = Form1.ActivateSubject
    Private Sub CheckedListBox1_SelectedValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles CheckedListBox1.SelectedValueChanged
       If HaveActSubject = False Then
            MsgBox("Sorry! Subject should be activated six month before registration.")
       End If
       Return
    End Sub
 End Class

Answer 1

Public Class Form1
    Public Function ActivateSubject(itm as string) As String
        Return ListBox2.Items.Contains(itm)
    End Function
End Class

Public Class Form2
    Dim HaveActSubject As Boolean = Form1.ActivateSubject
    Private Sub CheckedListBox1_SelectedValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles CheckedListBox1.SelectedValueChanged
       If Form1.ActivateSubject(CheckedListBox1.selectedValue) = False Then
            MsgBox("Sorry! Subject should be activated six month before registration.")
       End If
       Return
    End Sub
 End Class