线程计时器
更新：2007 年 11 月
System.Threading.Timer 类可用于定期在单独的线程上运行任务。例如，可以使用线程计时器来检查数据库的状态和完整性，或备份重要文件。
线程计时器示例
下面的示例每两秒启动一项任务，并使用一个标志来启动停止该计时器的 Dispose 方法。此示例将状态显示到输出窗口上，因此在测试代码前，应按下 Ctrl+Alt+O 显示该窗口。
Class StateObjClass
' Used to hold parameters for calls to TimerTask
Public SomeValue As Integer
Public TimerReference As System.Threading.Timer
Public TimerCanceled As Boolean
End Class
Sub RunTimer()
Dim StateObj As New StateObjClass
StateObj.TimerCanceled = False
StateObj.SomeValue = 1
Dim TimerDelegate As New Threading.TimerCallback(AddressOf TimerTask)
' Create a timer that calls a procedure every 2 seconds.
' Note: There is no Start method; the timer starts running as soon as
' the instance is created.
Dim TimerItem As New System.Threading.Timer(TimerDelegate, StateObj, _
2000, 2000)
StateObj.TimerReference = TimerItem ' Save a reference for Dispose.
While StateObj.SomeValue < 10 ' Run for ten loops.
System.Threading.Thread.Sleep(1000) ' Wait one second.
End While
StateObj.TimerCanceled = True ' Request Dispose of the timer object.
End Sub
Sub TimerTask(ByVal StateObj As Object)
Dim State As StateObjClass = CType(StateObj, StateObjClass)
' Use the interlocked class to increment the counter variable.
System.Threading.Interlocked.Increment(State.SomeValue)
System.Diagnostics.Debug.WriteLine("Launched new thread " & Now)
If State.TimerCanceled Then ' Dispose Requested.
State.TimerReference.Dispose()
System.Diagnostics.Debug.WriteLine("Done " & Now)
End If
End Sub
当 System.Windows.Forms.Timer 对象不可用时（例如在开发控制台应用程序时），线程计时器特别有用。