User idle time calculation using mouse and keyboard

Option Strict On


Imports System.Runtime.InteropServices

Public Class IdleTime

    Public Structure LASTINPUTINFO
        Public cbSize As UInteger
        Public dwTime As UInteger
    End Structure

    'API call that let us detect any keyboard and/or mouse activity
    <DllImport("user32.dll")> _
    Private Shared Function GetLastInputInfo(ByRef plii As LASTINPUTINFO) As Boolean
    End Function

    'Returns the time since last user activity
    Public Function GetInactiveTime() As Nullable(Of TimeSpan)
        Dim info As LASTINPUTINFO = New LASTINPUTINFO
        info.cbSize = CUInt(Marshal.SizeOf(info))
        If (GetLastInputInfo(info)) Then
            Return TimeSpan.FromMilliseconds(Environment.TickCount - info.dwTime)
        Else
            Return Nothing
        End If
    End Function

End Class

Private IdleTimer As IdleTime

'check autolock time / 10 minutes default
AutoLockTime = 600

If AutoLockTime <= 0 Then
    InactivityTimer.Enabled = False     'Disabled
Else
    AutoLockTime = AutoLockTime + 10    'Plus 10 Seconds Allowance
    InactivityTimer.Enabled = True      'Activate Checking of Idle
End If

Private Sub InactivityTimer_Tick(sender As System.Object, e As System.EventArgs) Handles InactivityTimer.Tick

            Application.DoEvents()

            If IS_BUSY_PROCESSING Then Exit Sub

            'Calculates for how long we have been idle
            Dim inactiveTime = IdleTimer.GetInactiveTime

If (inactiveTime Is Nothing) Or (AutoLockTime <= 0) Then

                InactivityTimer.Enabled = False

            ElseIf (inactiveTime.Value.TotalSeconds > 10) Then

                Dim DisplayMinutes As Integer = (AutoLockTime - 10) / 60
                Dim DisplayTime As Integer = AutoLockTime - (inactiveTime.Value.TotalSeconds)
                Text1.Text = String.Format("Idle in {0} minute/s, the system will automatically lock. {1} time remaining.", DisplayMinutes, SecondsToHours(DisplayTime)))

                If inactiveTime.Value.TotalSeconds >= AutoLockTime Then
                    'perform screen lock
                    PerformLockScreen() 
                End If

            Else
                'StatusBarMessage()
            End If
        End Sub