防止开发人员在设计时多次放置UserControl

因为这种形式很容易使用,新的和处理,它不适用于打断奶的形式。只有在这个相同的地方。您可以使用互斥体或此模块属性的某个单例即时,或其他通知方法,告知此模块已创建以及何时释放。

    Sub New()
    '  This call is required by the designer.
    InitializeComponent()

    If Not co Is Nothing Then Throw New Exception
    co = Me ' assign public propert in  module or singleton

    ' Add any initialization after the InitializeComponent() call.

End Sub

Protected Overrides Sub Dispose(ByVal disposing As Boolean)
    Try
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
    Finally
        co = Nothing
        MyBase.Dispose(disposing)
    End Try
End Sub

Module common
Property co As UserControl1

结束模块

最后我结束了。。。

Private Sub Me_ParentChanged(sender As Object, e As EventArgs) Handles Me.ParentChanged

    Dim _ParentForm = DirectCast(Me.FindForm, Control)
    Dim _ControlName As String

    If _ParentForm IsNot Nothing Then
        For Each _Control As Control In _ParentForm.Controls
            If TypeOf _Control Is MyUserControl AndAlso _Control IsNot Me Then
                Throw New ArgumentOutOfRangeException("", "You can place only one " & _ControlName & " control per form.")
            End If
            _Control = _ParentForm.GetNextControl(_Control, True)
        Next
    End If

End Sub