防止开发人员在设计时多次放置 UserControl

Question

我正在研究 UserControl，我正在寻找一种方法来防止开发人员放置这个 UserControl不止一次变成一个表格。所有这些都在 设计时间 中完成。换句话说，如果我的 UserControl 已经放置到 ParentForm 或不在 设计时间(!!!)，并且防止 第二个放置 如果那里已经有一个？

我尝试了类似下面的示例...首先我不确定这是否是 "correct" 方式，其次我找不到如何删除或停止放置 UserControl如果已经有一个。

同样，所有这些都在设计时！！！

Private Sub MyUserControl_Load(sender As Object, e As EventArgs) Handles MyBase.Load 
    Dim _Count As Integer
    Dim _UserControl As MyUserControl
    For Each _UserControl In Me.ParentForm.Controls
        If _UserControl.Name.Contains("MyUserControl") Then
            _Count += 1
        End If
    Next
    If _Count > 1 Then
        MsgBox("Control have been placed.")
    Else
        MsgBox("Control haven't placed yet.")
    End If
End Sub

Answer 1

因为这个相同的表格很容易使用新的和处置，它不适用于 beat weans 表格。只有在这个相同的。你可以使用这个模块的互斥锁或一些单例实例属性或其他通知方法，它是创建的以及何时被处理的。

    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

模块结束

Answer 2

最后我就这样结束了...

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

防止开发人员在设计时多次放置 UserControl

Prevent developer from placing a UserControl more than one time in Design Time

vb.net

user-controls

winforms

visual-studio-2017