文章編號: 231298 - 上次校閱: 2004年7月13日 - 版次: 3.1

如何使用與 Visual Basic SetWaitableTimer

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結論

許多程式設計人員使用睡眠 API 函數來暫停程式執行。其中一個使用睡眠的缺點是它會暫停應用程式正在執行中，執行緒和重新應用程式有開啟任何視窗將不繪製正確。這可能會對使用者顯示 unattractive 使用者介面。睡眠的替代方法是使用 SetWaitableTimer 這將允許螢幕重繪、接收 DDE 訊息等等。

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其他相關資訊

下列程式碼範例會說明如何 SetWaitableTimer API 使用。

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雖說是逐步範例

在 Visual Basic 中啟動新的標準 EXE 專案。預設會建立 Form1。
在 Form1 上放置兩個 CommandButtons。

將下列程式碼貼到 Form1 的程式碼模組：

Option Explicit

' Sleep API is declared in the form to keep the
' SetWaitableTimer code in its own re-usable module.
Private Declare Sub Sleep Lib "kernel32" ( _
    ByVal dwMilliseconds As Long)

Private Sub Command1_Click()
    Command1.Enabled = False
    Wait 10 ' seconds
    Command1.Enabled = True
End Sub

Private Sub Command2_Click()
    Command2.Enabled = False
    Sleep 10000 ' milliseconds
    Command2.Enabled = True
End Sub

Private Sub Form_Load()
    With Form1
        .Height = 1400
        .Width = 2400
    End With
    With Command1
        .Move 100, 100, 2000, 300
        .Caption = "SetWaitableTimer"
    End With
    With Command2
        .Move 100, 500, 2000, 300
        .Caption = "Sleep"
    End With
End Sub

從 [專案] 功能表中，按一下 [加入模組]，以將新的模組 (Module1) 加入至專案]。

下列程式碼貼到 Module1 中：

Option Explicit

Private Type FILETIME
    dwLowDateTime As Long
    dwHighDateTime As Long
End Type

Private Const WAIT_ABANDONED& = &H80&
Private Const WAIT_ABANDONED_0& = &H80&
Private Const WAIT_FAILED& = -1&
Private Const WAIT_IO_COMPLETION& = &HC0&
Private Const WAIT_OBJECT_0& = 0
Private Const WAIT_OBJECT_1& = 1
Private Const WAIT_TIMEOUT& = &H102&

Private Const INFINITE = &HFFFF
Private Const ERROR_ALREADY_EXISTS = 183&

Private Const QS_HOTKEY& = &H80
Private Const QS_KEY& = &H1
Private Const QS_MOUSEBUTTON& = &H4
Private Const QS_MOUSEMOVE& = &H2
Private Const QS_PAINT& = &H20
Private Const QS_POSTMESSAGE& = &H8
Private Const QS_SENDMESSAGE& = &H40
Private Const QS_TIMER& = &H10
Private Const QS_MOUSE& = (QS_MOUSEMOVE _
                            Or QS_MOUSEBUTTON)
Private Const QS_INPUT& = (QS_MOUSE _
                            Or QS_KEY)
Private Const QS_ALLEVENTS& = (QS_INPUT _
                            Or QS_POSTMESSAGE _
                            Or QS_TIMER _
                            Or QS_PAINT _
                            Or QS_HOTKEY)
Private Const QS_ALLINPUT& = (QS_SENDMESSAGE _
                            Or QS_PAINT _
                            Or QS_TIMER _
                            Or QS_POSTMESSAGE _
                            Or QS_MOUSEBUTTON _
                            Or QS_MOUSEMOVE _
                            Or QS_HOTKEY _
                            Or QS_KEY)

Private Declare Function CreateWaitableTimer Lib "kernel32" _
    Alias "CreateWaitableTimerA" ( _
    ByVal lpSemaphoreAttributes As Long, _
    ByVal bManualReset As Long, _
    ByVal lpName As String) As Long
    
Private Declare Function OpenWaitableTimer Lib "kernel32" _
    Alias "OpenWaitableTimerA" ( _
    ByVal dwDesiredAccess As Long, _
    ByVal bInheritHandle As Long, _
    ByVal lpName As String) As Long
    
Private Declare Function SetWaitableTimer Lib "kernel32" ( _
    ByVal hTimer As Long, _
    lpDueTime As FILETIME, _
    ByVal lPeriod As Long, _
    ByVal pfnCompletionRoutine As Long, _
    ByVal lpArgToCompletionRoutine As Long, _
    ByVal fResume As Long) As Long
    
Private Declare Function CancelWaitableTimer Lib "kernel32" ( _
    ByVal hTimer As Long)
    
Private Declare Function CloseHandle Lib "kernel32" ( _
    ByVal hObject As Long) As Long
    
Private Declare Function WaitForSingleObject Lib "kernel32" ( _
    ByVal hHandle As Long, _
    ByVal dwMilliseconds As Long) As Long
    
Private Declare Function MsgWaitForMultipleObjects Lib "user32" ( _
    ByVal nCount As Long, _
    pHandles As Long, _
    ByVal fWaitAll As Long, _
    ByVal dwMilliseconds As Long, _
    ByVal dwWakeMask As Long) As Long

Public Sub Wait(lNumberOfSeconds As Long)
    Dim ft As FILETIME
    Dim lBusy As Long
    Dim lRet As Long
    Dim dblDelay As Double
    Dim dblDelayLow As Double
    Dim dblUnits As Double
    Dim hTimer As Long
    
    hTimer = CreateWaitableTimer(0, True, App.EXEName & "Timer")
    
    If Err.LastDllError = ERROR_ALREADY_EXISTS Then
        ' If the timer already exists, it does not hurt to open it
        ' as long as the person who is trying to open it has the
        ' proper access rights.
    Else
        ft.dwLowDateTime = -1
        ft.dwHighDateTime = -1
        lRet = SetWaitableTimer(hTimer, ft, 0, 0, 0, 0)
    End If
    
    ' Convert the Units to nanoseconds.
    dblUnits = CDbl(&H10000) * CDbl(&H10000)
    dblDelay = CDbl(lNumberOfSeconds) * 1000 * 10000
    
    ' By setting the high/low time to a negative number, it tells
    ' the Wait (in SetWaitableTimer) to use an offset time as
    ' opposed to a hardcoded time. If it were positive, it would
    ' try to convert the value to GMT.
    ft.dwHighDateTime = -CLng(dblDelay / dblUnits) - 1
    dblDelayLow = -dblUnits * (dblDelay / dblUnits - _
        Fix(dblDelay / dblUnits))
    
    If dblDelayLow < CDbl(&H80000000) Then
        ' &H80000000 is MAX_LONG, so you are just making sure
        ' that you don't overflow when you try to stick it into
        ' the FILETIME structure.
        dblDelayLow = dblUnits + dblDelayLow
        ft.dwHighDateTime = ft.dwHighDateTime + 1 
    End If 
    
    ft.dwLowDateTime = CLng(dblDelayLow)
    lRet = SetWaitableTimer(hTimer, ft, 0, 0, 0, False)
    
    Do
        ' QS_ALLINPUT means that MsgWaitForMultipleObjects will
        ' return every time the thread in which it is running gets
        ' a message. If you wanted to handle messages in here you could,
        ' but by calling Doevents you are letting DefWindowProc
        ' do its normal windows message handling---Like DDE, etc.
        lBusy = MsgWaitForMultipleObjects(1, hTimer, False, _
            INFINITE, QS_ALLINPUT&)
        DoEvents
    Loop Until lBusy = WAIT_OBJECT_0
    
    ' Close the handles when you are done with them.
    CloseHandle hTimer

End Sub

執行專案。
按一下 [睡眠] 按鈕。雖然應用程式在休眠狀態，請注意並不重繪螢幕 (拖曳頂端的應用程式的另一個視窗，然後將其拖曳離開)。然後，嘗試與 SetWaitableTimer 按鈕相同的測試。

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?考

如需詳細資訊按一下面的文件編號，檢視「 Microsoft 知識庫」中的發行項:

184796? (http://support.microsoft.com/kb/184796/EN-US/ ) 如何以非同步的程序呼叫使用 waitable 計時器

Microsoft Win32 軟體開發人員套件的文件 SetWaitableTimer]、 [MsgWaitForMultipleObjects] 和 [CloseHandle API 呼叫。

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這篇文章中的資訊適用於:

Microsoft Visual Basic 5.0 Learning Edition
Microsoft Visual Basic 6.0 Learning Edition
Microsoft Visual Basic 5.0 Professional Edition
Microsoft Visual Basic 6.0 Professional Edition
Microsoft Visual Basic 5.0 Enterprise Edition
Microsoft Visual Basic Enterprise Edition for Windows 6.0
Microsoft Visual Basic 4.0 Professional Edition

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按一下這裡查看此文章的英文版本：231298? (http://support.microsoft.com/kb/231298/en-us/ )

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如何使用與 Visual Basic SetWaitableTimer

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結論

其他相關資訊

雖說是逐步範例

?考

這篇文章中的資訊適用於:

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