这是一篇旧文档

一个回调函数的演示：
Public Class frmMain

    Declare Function SetTimer Lib "user32" (ByVal hwnd As Int32, ByVal nIDEvent As Int32, ByVal uElapse As Int32, ByVal lpTimerFunc As TP) As Int32
    Declare Function KillTimer Lib "user32" (ByVal hwnd As Int32, ByVal nIDEvent As Int32) As Int32

    Delegate Function TP(ByVal hwnd As Int32, ByVal nIDEvent As Int32, ByVal uElapse As Int32, ByVal lpTimerFunc As Int32) As Integer

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        SetTimer(Me.Handle, 0, 1, AddressOf TimerProc)
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        KillTimer(Me.Handle, 0)
    End Sub

    Dim i As Integer = 0
    Function TimerProc(ByVal hwnd As Int32, ByVal nIDEvent As Int32, ByVal uElapse As Int32, ByVal lpTimerFunc As Int32) As Integer
        i += 1
        Me.Text = i
    End Function

End Class
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