c# - 安全地从线程中引发事件

Question

我在从非 UI 线程引发的事件方面遇到一些问题，因为我不希望必须在添加到 Form1 中的线程的每个事件处理程序上处理 If me.invokerequired。

我确定我已经在某处阅读过如何使用委托(delegate)事件(在 SO 上)，但我找不到它。

Public Class Form1

    Private WithEvents _to As New ThreadedOperation

    Private Sub Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button.Click
        _to.start()
    End Sub

    Private Sub _to_SomthingHappend(ByVal result As Integer) Handles _to.SomthingHappend
        TextBox.Text = result.ToString //cross thread exception here
    End Sub

End Class

Public Class ThreadedOperation

    Public Event SomthingHappend(ByVal result As Integer)
    Private _thread As Threading.Thread

    Public Sub start()
        If _thread Is Nothing Then
            _thread = New Threading.Thread(AddressOf Work)
        End If
        _thread.Start()
    End Sub

    Private Sub Work()
        For i As Integer = 0 To 10
            RaiseEvent SomthingHappend(i)
            Threading.Thread.Sleep(500)
        Next
    End Sub

End Class

Answer 1

您从 Control 派生了您的类。有点不寻常，但如果控件实际上托管在窗体上，则可以使用 Me.Invoke() 来编码调用。例如:

  Private Delegate Sub SomethingHappenedDelegate(ByVal result As Integer)

  Private Sub Work()
    For i As Integer = 0 To 10
      Me.Invoke(New SomethingHappenedDelegate(AddressOf SomethingHappenedThreadSafe), i)
      Threading.Thread.Sleep(500)
    Next
  End Sub

  Private Sub SomethingHappenedThreadSafe(ByVal result As Integer)
    RaiseEvent SomthingHappend(result)
  End Sub

如果此类对象实际上并未托管在表单上，​​则需要传递对表单的引用，以便它可以调用 Invoke():

  Private mHost As Form

  Public Sub New(ByVal host As Form)
    mHost = host
  End Sub

并使用 mHost.Invoke()。或 BeginInvoke()。

本书的最后一个技巧是使用你的主启动窗体作为同步对象。这并不完全安全，但在 99% 的情况下都有效:

  Dim main As Form = Application.OpenForms(0)
  main.Invoke(New SomethingHappenedDelegate(AddressOf SomethingHappenedThreadSafe), i)

请注意，WF 中有一个错误会阻止 OpenForms() 在动态重新创建打开的表单时准确跟踪它们。