Vb.net Mobile - turn display backlight on AND off again

I'm working on a Windows Mobile application using vb.net (VS2008)

The application has 2 buttons.
Button1 should turn backlight fully on and leave it that way
Button2 should release the settings from button1 and give power control back to the mobile device.

I am a beginner in mobile programming and would appreciate if the help would come as the exact code. Thanks in advance !

I already have a class that should be able to do this, but I don't know how to use it. ( see code )
Public Class Backlight
'ensure the power requirement is released
Protected Overrides Sub Finalize()
End Sub
'handle to the power requirement
Private handle As IntPtr
Private Enum PowerState
PwrDeviceUnspecified = -1
'full on
D0 = 0
'low power
D1 = 1
D2 = 2
D3 = 3
D4 = 4
PwrDeviceMaximum = 5
End Enum
'keep the backlight lit
Public Sub Activate()
'request full power
handle = SetPowerRequirement("BKL1:", PowerState.D0, 1, IntPtr.Zero, 0)
End Sub
'release power requirement
Public Sub Release()
If handle.ToInt32() <> 0 Then
Dim result As Integer
result = ReleasePowerRequirement(handle)
handle = IntPtr.Zero
End If
End Sub
Private Declare Function SetPowerRequirement Lib "coredll.dll" (ByVal pvDevice As String, ByVal DeviceState As PowerState, ByVal DeviceFlags As Integer, ByVal pvSystemState As IntPtr, ByVal StateFlags As Integer) As IntPtr
Private Declare Function ReleasePowerRequirement Lib "coredll.dll" (ByVal handle As IntPtr) As Integer
End Class

Open in new window

Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

I'm not sure it will help.  It is not VB. But it is something:
(please read all - in the end the code with the backlight)
In order to wake up the device, you can that:
void RunAtTime()

SYSTEMTIME t; memset(&t, 0, sizeof(SYSTEMTIME));

t.wMonth = 7;
t.wDay = 15;
t.wYear = 2009;
t.wHour = 18;
t.wMinute = 45;

CeRunAppAtTime(_T("\\Windows\\iexplorer.exe", &t);

 Here is an example from MSDN (but it is again C++):
Only here it looks like VB:
karstiemanAuthor Commented:
Ok, i've got a bit further.
If I use the code: --> SetPowerRequirement("BKL1:", PowerState.D0, 1, IntPtr.Zero, 0) <--
Then the screen we be lit and keep lit.

But what code can I use to turn the light of again so the mobile device goes back to normal ?
ReleasePowerRequirement(handle from SetPower here);

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Cloud Class® Course: Python 3 Fundamentals

This course will teach participants about installing and configuring Python, syntax, importing, statements, types, strings, booleans, files, lists, tuples, comprehensions, functions, and classes.

karstiemanAuthor Commented:
Thank you Pgnatyuk,

So if I'm right this should work ?

dim handle as intptr = SetPowerRequirement("BKL1:", PowerState.D0, 1, IntPtr.Zero, 0)
I hope so. I don't know VB to confirm that this ok. It looks correct.
I think I even used just CloseHandle and it was okay.
karstiemanAuthor Commented:
Just tested and it doesn't work... :-(

How do you use CloseHandle ?

Bye the way, should the handle always be the same ?
Because by using the following code , I found that handle is always the same...

dim handle as intptr = intptr.zero
MsgBox(Handle.ToInt32)  --> shows  2080980208
SetPowerRequirement("BKL1:", PowerState.D0, 1, IntPtr.Zero, 0)
MsgBox(Handle.ToInt32)  --> shows   2080980208
MsgBox(Handle.ToInt32)  --> shows  2080980208
The handle is ok. You could changed other parameters, so it's always on. When you close the app, the backlight behaves well?
In the first comment I posted the link: http://www.hjgode.de/wp/2009/07/14/howto-run-an-application-periodically/
 //Switch Backlight ON
hPower = SetPowerRequirement(_T("BKL1:"), D0, POWER_NAME, NULL, 0); //POWER_FORCE
//set to full power

 Then a background thread with SystemIdleTimerReset():
DWORD WINAPI ThreadProc(LPVOID lpParameter)
 return 0;
For the backlight: dont forget to release the power request:
if(hPower != NULL)
 HRESULT result = ReleasePowerRequirement(hPower);
Accordingly to MSDN this code ReleasePowerRequirement(s_hBacklightReq)) should work. The arcticle even has name "Program Applications to Turn the Smartphone Backlight Off and On" : http://msdn.microsoft.com/en-us/library/aa455153.aspx
In the SDK you can find Power Manager sample: http://msdn.microsoft.com/en-us/library/ms880669.aspx
Try it.
the sad fact is that once SetPowerRequirement() is called, it quite often never comes back to normal :)

you might try to broadcast WM_SETTINGCHANGED or WM_WININICHANGED with magic number 0xF2 as WPARAM, but it may not work. It seems you need to kick off device.exe (as it deals with drivers) to get it 'reset' its state.
Yes, I do remember something about the broadcast: SendMessage(HWND_BROADCAST,WM_SETTIGNSCHANGE,0xF2,0)
Do you use SystemIdleTimerReset() or touched the registry settings defining the timeouts?
BTW, here is the thread about the same: http://www.experts-exchange.com/Programming/Languages/C_Sharp/Q_22921526.html?sfQueryTermInfo=1+setpowerrequir
karstiemanAuthor Commented:
I've got it working now. The solution is really stupid though...

When calling:
dim handle as intptr = SetPowerRequirement("BKL1:", PowerState.D0, 1, IntPtr.Zero, 0)

You have to wait at least 30seconds before calling:

Then it works.
Thanks for the help !
karstiemanAuthor Commented:
Thanks for the help ! It's appreciated !
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Smartphone Programming

From novice to tech pro — start learning today.