如果 child 只是表单的副本，如何检测 MDIChild？

Question

我有frm_Child和frm_Parent，我把frm_Parent的isMDIContainer设为true

在 frm_Parent 我有 2 个按钮

btn_Create - 创建另一个 mdi child
btn_Detect - 检测活动 mdi Child (When I say active it means that I set my focused on it)

frm_Parent代码：

Public Class frm_Parent

   Public my_variable As String

   Private Sub btn_create_Click(sender As Object, e As EventArgs) Handles btn_create.Click
      my_variable += 1
      Call New frm_Child() With {.MdiParent = Me}.Show()
   End Sub

   Private Sub btn_Detect_Click(sender As Object, e As EventArgs) Handles btn_Detect.Click
      'Code to detect active mdi child
   End Sub

End Class

然后我有 frm_Child，其中我有 label1.text，label1.text 的值将自动获得 form_load，这完全取决于 my_variable 在 frm_Parent

frm_Child代码：

Public Class frm_Child

   Private Sub frm_Child_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      Label1.Text = frm_Parent.my_variable
   End Sub

End Class

示例屏幕截图，如果我创建 4 个新 frm_Child

问题： 如何以编程方式检测活动的 mdi child 并将 label1.text 显示到消息框？ (note: active mean that I set my on it.)

我试过这样的东西，

Private Sub btn_Detect_Click(sender As Object, e As EventArgs) Handles btn_Detect.Click
    'Code to detect active mdi child
    Dim activeChild As Form = me.ActiveMdiChild
    MsgBox(activeChild.label1.text)
End Sub

还有这个，我修改了the example from MSDN

Private Sub btn_Detect_Click(sender As Object, e As EventArgs) Handles btn_Detect.Click
    'Code to detect active mdi child
    Dim activeChild As Form = Me.ActiveMdiChild

    ' If there is an active child form, find the active control, which
    ' in this example should be a RichTextBox.
    If (Not activeChild Is Nothing) Then
        Try
            Dim theLabel As Label = CType(activeChild.ActiveControl, Label)
            MsgBox(theLabel.Text)
        Catch
            MessageBox.Show("You need to select an active form.")
        End Try
    End If
End Sub

Answer 1

因此，要总结答案中的评论，您需要通过父级的 ActiveMdiChild 属性获取子表单并将其转换为适当的类型，以便能够访问该类型的成员。

Answer 2

就我个人而言，我认为您应该将 "my_variable" 值传递给 child 表单的 Constructor，但要遵循 jmcilhinney 的建议 casting，你应该这样抓取它（而不是使用默认实例）：

Private Sub frm_Child_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim parent As frm_Parent = DirectCast(Me.MdiParent, frm_Parent)
    Me.Label1.Text = parent.my_variable
End Sub

同样，下面是您如何投射 MdiChild 并在 "detect" 按钮中获取标签：

Private Sub btn_Detect_Click(sender As Object, e As EventArgs) Handles btn_Detect.Click
    If Not IsNothing(Me.ActiveMdiChild) Then
        Dim child As frm_Child = DirectCast(Me.ActiveMdiChild, frm_Child)
        MessageBox.Show(child.Label1.Text)
    End If
End Sub

当然，如果您要使用不同类型的 MdiChildren，那么您要么必须进行额外检查并转换为正确的类型，要么使用一个 Interface，所有 children 实现并转换为该接口。

如果 child 只是表单的副本，如何检测 MDIChild？

How to detect MDIChild if the child is just a duplicate of a form?

vb.net

mdi