How long the PC has been started? - vb.net

Question

I would like to know how long the PC has been started.
That's why I made the following routine:
Public Function LipPCIsOn() As String
Dim iTempoPC As Integer
Dim tTempoPC As TimeSpan
Dim strTempoPC As String
iTempoPC = System.Environment.TickCount
tTempoPC = TimeSpan.FromMilliseconds(iTimePC)
strTempoPC = tTempoPC.Duration.ToString("hh:mm:ss")
Return strTempoPC
End Function
But I do not understand, the PC despite having been started by 3 minutes it tells me:
7:54:36
Where's the mistake?
Thank you all

Answer 1

There may be some other source of the last power-on time, but you can use the Windows System Event Log to get the last event from Kernel-Boot:
Function GetLastPowerOn() As DateTime?
Dim systemEventLog = New EventLog()
systemEventLog.Log = "System"
Dim lastPowerOn = systemEventLog.Entries.Cast(Of EventLogEntry).
Where(Function(eu) eu.Source = "Microsoft-Windows-Kernel-Boot").
OrderByDescending(Function(ev) ev.TimeGenerated).FirstOrDefault()
Return lastPowerOn?.TimeGenerated
End Function
I do not know the behaviour for if there is no entry, so I assumed that a Nullable(Of DateTime) would do. If you want to clear your System event log, you could let us know what happens; I don't want to do that.
Unfortunately, it takes ages to return a value (e.g. about 7 seconds on this computer), so you might want to call it asynchronously. Here is an example which uses one button and two labels on a form:
Public Class Form1
Dim tim As Timer
Friend Async Function GetLastPowerOnAsync() As Task(Of DateTime?)
Dim systemEventLog = New EventLog() With {.Log = "System"}
Dim tsk = Await Task.Factory.StartNew(Function()
Return systemEventLog.Entries.Cast(Of EventLogEntry).
Where(Function(eu) eu.Source = "Microsoft-Windows-Kernel-Boot").
OrderByDescending(Function(ev) ev.TimeGenerated).
FirstOrDefault()
End Function)
Return tsk?.TimeGenerated
End Function
Sub timTick(sender As Object, e As EventArgs)
Label1.Text = DateTime.Now.ToString("HH:mm:ss")
End Sub
Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim lpo = Await GetLastPowerOnAsync()
If lpo.HasValue Then
Label2.Text = lpo.Value.ToString("yyyy-MM-dd HH:mm:ss")
Else
Label2.Text = "No System event log entry with a source of Microsoft-Windows-Kernel-Boot entry found."
End If
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
tim = New Timer() With {.Interval = 500}
AddHandler tim.Tick, AddressOf timTick
tim.Start()
End Sub
Private Sub Form1_FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing
RemoveHandler tim.Tick, AddressOf timTick
tim.Dispose()
End Sub
End Class

Answer 2

Thank you all.
I just wanted to point out that:
1) my PC did not make a real shutdown but a suspension;
2) the correct code I rewrote is:
Public Function LipPCIsOnNew() As String
Dim EventoLogApp As New System.Diagnostics.EventLog("System")
Dim OraACCENSIONE As Date, stMachineName As String
' search from the end, to find the last boot faster
For i = EventoLogApp.Entries.Count - 1 To 1 Step -1
If EventoLogApp.Entries(i).InstanceId.ToString = 1 Then
OraACCENSIONE = EventoLogApp.Entries(i).TimeGenerated
stMachineName = EventoLogApp.Entries(i).MachineName.ToString
Exit For
End If
Next
Return OraACCENSIONE.ToString
End Function
Now everything is ok
Thank you all