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更改对对象的引用时WithEvents,Visual Basic 中是否保留其 s?EventHandler

假设我已经声明了一个按钮,触发事件:

Private WithEvents _MyButton

现在我订阅了一个事件处理程序:

Private Sub _MyButton_Click() Handles _MyButton.Click 
  ' Here I DoClick()
End Sub

当我更改按钮对象的实例时,是否仍会调用该DoClick()函数,如下所示?

_MyButton = New Button()
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1 回答 1

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这让我很好奇,所以我编写了一个小型控制台应用程序来可视化如果您使用计时器进行此实验会发生什么:

Private WithEvents _t As New Timers.Timer With {.Enabled = True}
Private Sub _t_Elapsed(sender As Object, e As Timers.ElapsedEventArgs) Handles _t.Elapsed
    Console.WriteLine("tick")
End Sub

Sub Main()
    ' let it tick for 5 seconds
    Task.Delay(5000).Wait()

    ' destroy the current timer
    Console.WriteLine("destroying this timer")
    _t.Dispose()
    _t = Nothing

    ' add a little pause
    Task.Delay(1000).Wait()

    ' create a new timer
    Console.WriteLine("creating a new timer")
    _t = New Timers.Timer With {.Enabled = True}

    ' let it tick for 5 seconds
    Task.Delay(5000).Wait()

End Sub

如果您运行此代码,您会发现它确实在_t替换实例时附加了事件处理程序。我不知道它是怎么做到的,但神奇之处可能在于Handles关键字。无论如何,答案是肯定的。

于 2013-03-11T12:06:23.460 回答