How does Windows know when to call the screensaver?

Is there an API-call or something to check how much time passed since the last keypress
or mouse movement?

Timer Control

Well, this might work for one single application but not for the whole system. using just a timer control I couldn't access the events of all other apps running, could I? Subclassing Windows isn't possible, too (would be quite nice ;-))!

Create a new form and add a label and a timer called Label1 and Timer1.

Use the GetAsyncKeyState to see if a key was pressed since the last time we checked the key.
And the GetCursorPos to check the last cursor position.

Code:

---

Option Explicit
Private Declare Function GetAsyncKeyState Lib "user32" (ByVal vKey As Long) As Integer
Private Declare Function GetCursorPos Lib "user32" (lpPoint As POINTAPI) As Long
Private Type POINTAPI
        x As Long
        y As Long
End Type


Private Sub Form_Load()
    'Init timer
    Timer1.Interval = 100
    Timer1.Enabled = True
End Sub

Private Sub Timer1_Timer()
    Dim bActive As Boolean
    Dim iCounter As Integer        'Counter to walk throug all key's
    Dim pCursPos As POINTAPI        'Cursor pos
    Static plCursPos As POINTAPI    'Store last cursor posistion
    Static datTime As Date
   
    'Loop through every key
    For iCounter = 1 To 256
        If GetAsyncKeyState(iCounter) <> 0 Then
            'Key was pressed since last time we checked
            bActive = True
            Exit For
        End If
    Next
   
    'Get the cursor pos
    GetCursorPos pCursPos
   
    'Check the cursor pos with the last cursorpos
    If pCursPos.x <> plCursPos.x Or pCursPos.y <> plCursPos.y Then
        bActive = True
    End If
   
    'Store the cursor pos for next time
    plCursPos = pCursPos
   
    'There has been some activity reset the time
    If bActive = True Then
        datTime = Now
    End If
    Label1 = "Inactive for " & DateDiff("s", datTime, Now) & " sec."
End Sub

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Vincent van den Braken
EMail: [email protected]
ICQ: 15440110
Homepage: http://www.azzmodan.demon.nl