VB.NET - Detecting when the computer wakes up.

Question

I have tried a suggestion that someone posted on Stack Overflow, however, it is not working. I can't seem to find the solution online. I wonder if it is even possible to detect when the computer wakes up from sleep in VB.NET. Heer is my code.

First, I put the AddHandler statement in the Form Load event.

AddHandler Microsoft.Win32.SystemEvents.PowerModeChanged, AddressOf SystemEvents_PowerModeChanged

Then I put the following Code in a sub routine.

`Private Sub SystemEvents_PowerModeChanged(ByVal sender As Object, ByVal e As PowerModeChangedEventArgs) ' Handles SystemEvents.PowerModeChanged

Select Case e.Mode

Case PowerModes.Resume

UpdateEventBellScheduleInformation()

Case PowerModes.StatusChange

Case PowerModes.Suspend

End Select

End Sub

I don't know what I am missing.

Answer 1

To detect when the computer wakes up from sleep in VB.NET, your approach using the SystemEvents.PowerModeChanged event is correct. The code you provided should work as intended, but here are a few things to check:

1. Ensure the Application is Running: Make sure that your application is running and not minimized or in the background when the wake event occurs.
2. Event Subscription: Verify that the AddHandler statement is indeed being executed. You can add a breakpoint or a debug message to confirm that the event is being subscribed to properly.
3. PowerMode Enumeration: Ensure that you are handling the PowerModes.Resume case correctly. This is where you should place the logic that needs to execute when the system resumes.
4. Dispose of Event Handlers: If your application closes or the form is disposed, ensure that you remove the event handler to prevent memory leaks.
5. Permissions: Sometimes, certain permissions or settings in the operating system may affect the ability to receive power mode change notifications.

If everything appears to be set up correctly and it still doesn't work, consider testing on a different machine or environment to rule out system-specific issues.

---

References:

• Power Management in Windows Forms
• System Wake-up Events

Answer 2

Hi @Marc Menzel ,

You can use the Windows API to detect wake-up events more directly.

Listen for the WM_POWERBROADCAST message using WndProc in your form. PBT_APMRESUMESUSPEND is sent when the system resumes from sleep.

Protected Overrides Sub WndProc(ByRef m As Message)
    Const WM_POWERBROADCAST As Integer = &H218
    Const PBT_APMRESUMESUSPEND As Integer = &H7

    If m.Msg = WM_POWERBROADCAST Then
        If m.WParam.ToInt32() = PBT_APMRESUMESUSPEND Then
            UpdateEventBellScheduleInformation()
        End If
    End If
    MyBase.WndProc(m)
End Sub

Best Regards.

Jiachen Li

---

If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Answer 3

Some people said WM_POWERBROADCAST is not always received (WinUI 3 thread : https://github.com/microsoft/WindowsAppSDK/discussions/2630)

This test that I converted from C# works on my Windows 10 OS :

Imports System.Runtime.InteropServices

Public Class Form1

    Public Delegate Function DEVICE_NOTIFY_CALLBACK_ROUTINE(ByVal Context As IntPtr, ByVal Type As UInteger, ByVal Setting As IntPtr) As UInteger

    <StructLayout(LayoutKind.Sequential)>
    Public Structure DEVICE_NOTIFY_SUBSCRIBE_PARAMETERS
        Public Callback As DEVICE_NOTIFY_CALLBACK_ROUTINE
        Public Context As IntPtr
    End Structure

    <DllImport("Powrprof.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
    Public Shared Function PowerRegisterSuspendResumeNotification(Flags As UInteger, Recipient As IntPtr, ByRef RegistrationHandle As IntPtr) As UInteger
    End Function

    Public Const DEVICE_NOTIFY_CALLBACK As Integer = 2

    Public Const PBT_APMQUERYSUSPEND = &H0
    Public Const PBT_APMQUERYSTANDBY = &H1
    Public Const PBT_APMQUERYSUSPENDFAILED = &H2
    Public Const PBT_APMQUERYSTANDBYFAILED = &H3
    Public Const PBT_APMSUSPEND = &H4
    Public Const PBT_APMSTANDBY = &H5
    Public Const PBT_APMRESUMECRITICAL = &H6
    Public Const PBT_APMRESUMESUSPEND = &H7
    Public Const PBT_APMRESUMESTANDBY = &H8
    Public Const PBTF_APMRESUMEFROMFAILURE = &H1
    Public Const PBT_APMBATTERYLOW = &H9
    Public Const PBT_APMPOWERSTATUSCHANGE = &HA
    Public Const PBT_APMOEMEVENT = &HB
    Public Const PBT_APMRESUMEAUTOMATIC = &H12
    Public Const PBT_POWERSETTINGCHANGE = &H8013

    Private callbackDelegate As DEVICE_NOTIFY_CALLBACK_ROUTINE

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        callbackDelegate = New DEVICE_NOTIFY_CALLBACK_ROUTINE(AddressOf DeviceNotifyCallbackRoutine)
        Dim dnsp As New DEVICE_NOTIFY_SUBSCRIBE_PARAMETERS()
        dnsp.Callback = callbackDelegate
        Dim pDeviceNotify As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(dnsp))
        Marshal.StructureToPtr(dnsp, pDeviceNotify, False)
        Dim pRegistrationHandle As IntPtr = IntPtr.Zero
        Dim nRet As UInteger = PowerRegisterSuspendResumeNotification(DEVICE_NOTIFY_CALLBACK, pDeviceNotify, pRegistrationHandle)
        Marshal.FreeHGlobal(pDeviceNotify)
    End Sub

    Private Shared Function DeviceNotifyCallbackRoutine(ByVal Context As IntPtr, ByVal Type As UInteger, ByVal Setting As IntPtr) As UInteger
        Console.Beep(5000, 10)
        ' PBT_APMSUSPEND, PBT_APMRESUMESUSPEND, PBT_APMRESUMEAUTOMATIC
        System.Diagnostics.Debug.WriteLine(String.Format("DeviceNotify - Type = 0x{0:X4}", Type))
        Return 0
    End Function
End Class