Question

我这样做：

    Delegate Sub SetTextBoxText_Delegate(ByVal [Label] As TextBox, ByVal [text] As String)
' The delegates subroutine.  

Public Sub SetTextBoxText_ThreadSafe(ByVal [Label] As TextBox, ByVal [text] As String)
    ' InvokeRequired required compares the thread ID of the calling thread to the thread ID of the creating thread.  
    ' If these threads are different, it returns true.  
    If [Label].InvokeRequired Then
        MsgBox("invoke")
        Dim MyDelegate As New SetTextBoxText_Delegate(AddressOf SetTextBoxText_ThreadSafe)
        Me.Invoke(MyDelegate, New Object() {[Label], [text]})
    Else
        MsgBox("noinvoke")
        [Label].Text = [text]
    End If
End Sub

然而它总是使用noinvoke。如果我尝试正常设置它会给我一个线程安全的警告，但不起作用。如果我强制调用然后它说控件没有创建？

有人可以帮忙吗？

Answer 1

这很可能是因为当您尝试访问控件时尚未创建控件。等到控件加载完毕，或使用Label.Created进行检查。像这样：

Public Sub SetTextBoxText_ThreadSafe(ByVal Label As TextBox, ByVal text As String)
    If Label.Created Then
        If Label.InvokeRequired Then
            MsgBox("invoke")
            Dim MyDelegate As New SetTextBoxText_Delegate(AddressOf SetTextBoxText_ThreadSafe)
            Me.Invoke(MyDelegate, New Object() {Label, text})
        Else
            MsgBox("noinvoke")
            Label.Text = text
        End If
    End If
End Sub

P.S。您不需要自定义委托类型，只需使用Action(Of TextBox, String)即可。您也不需要Label或text附近的方括号。

调用不会调用？

1 个答案: