Question

我正在开展一个项目，要求我对外部设备生成的5个独立事件做出反应，然后在一定延迟后做一些事情。这些事件通常会一次发生一次，但有时可能同时发生。这是一个坏主意，如果是这样，为什么？

Imports System.Windows.Threading
Class MainWindow

Private TimerList As List(Of DispatcherTimer)

Private Sub Window_Loaded(ByVal sender As System.Object, 
ByVal e As ystem.Windows.RoutedEventArgs) Handles MyBase.Loaded

TimerList = New List(Of DispatcherTimer)

    'Create 5 timers for the 5 events from external device
    For i As Integer = 1 To 5
        TimerList.Add(
            New DispatcherTimer(TimeSpan.FromSeconds(10), DispatcherPriority.Normal,
                            New System.EventHandler(AddressOf tmr_Tick),
                            Me.Dispatcher) With {.Tag = i}
                        )
    Next

End Sub

Public Sub SomeEventFromExternalDevice(ByVal ID As Integer) 'handles...

    Dim CurTimer = TimerList.Find(Function(x) x.Tag = ID)

    If Not CurTimer Is Nothing Then
        CurTimer.Start()
    End If

End Sub

Private Sub tmr_Tick(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim ID = DirectCast(sender.tag, Integer)

    Dim curTimer = TimerList.Find(Function(x) x.Tag = ID)

    curTimer.Stop()

    Select Case ID
        'change something on the UI to indicate that event x timer has elapsed
    End Select

End Sub

End Class

Answer 1

对此可能更好的解决方案是完全删除DispatcherTimer并使用普通线程执行此操作。

首先创建一个类来保存单个事件工作包 - 我添加了一种方法来传递延迟值，但如果它不符合您的需要，您可以省略它。这是一个简单的过程，它会让线程暂停延迟，然后引发一个新的事件让你捕获。如果您需要精确度，那么您可以使用秒表或其他方式实现延迟：

Public Class DelayThread
    ' Task information
    Private _ID As Integer
    Private _delay As Integer
    Event onDelayUp(ByVal ID As Integer)

    ' Constructor
    Public Sub New(ByVal myID As Integer, ByVal myDelay As Integer)
        _ID = myID
        _delay = myDelay
    End Sub

    Public Sub DelayProc()
        System.Threading.Thread.Sleep(_delay)
        RaiseEvent onDelayUp(_ID)
    End Sub
End Class

现在您的设备将触发此处处理的事件：

Public Sub SomeEventFromExtDevice(ByVal ID As Integer) 'Handles ...
        'get a "delay" value from somewhere, if you like
        Dim newDelayTask As New DelayThread(ID, delay)  'added delay here

        AddHandler newDelayTask.onDelayUp, AddressOf DoSomething

        Dim t As New System.Threading.Thread( _
        New System.Threading.ThreadStart(AddressOf newDelayTask.DelayProc))

        t.Priority = Threading.ThreadPriority.Normal 'whatever priority
        t.Start()

End Sub

这样，每次事件触发时，你都会启动一个等待延迟时间的新线程，DoSomething然后终止，在此过程中自行清理。

在这里你需要一些“DoSomething”程序：

 'declare this somewhere
 Delegate Sub dlgDoSomething(ByVal ID As Integer)

 Public Sub DoSomething(ByVal ID As Integer) 'hooked to onDelayUp @ runtime above
      'using "Me" here - if DoSomething is somewhere else 
      'you may need to refer to the main UI form instead  
      Me.Invoke(New dlgDoSomething(AddressOf uiDoSomething), New Object() {ID})
 End Sub

将从每个线程调用DoSomething过程，因此必须在主UI线程上调用 - 然后需要：

Public Sub uiDoSomething(ByVal ID As Integer)
        ' Do Something with ID - UI thread is now executing this so you are safe
End Sub

如果知道事件的确切顺序很重要 - 知道它们到达的时间和顺序 - 那么你可以在SomeEventFromExtDevice中添加一个时间戳并传递它。

您可能还想添加一些关闭应用程序的处理 - 这里没有检查以确保线程在处理后不会尝试编组到主窗体上，例如。

具有一个tick事件处理程序的多个DispatcherTimers

1 个答案: