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

Posted on 2009-07-14
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Last Modified: 2013-12-21
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()
 

Release()
 

End Sub
 

'handle to the power requirement
 

Private handle As IntPtr
 

 
 

Private Enum PowerState
 

PwrDeviceUnspecified = -1
 

'full on
 

D0 = 0
 

'low power
 

D1 = 1
 

'standby
 

D2 = 2
 

'sleep
 

D3 = 3
 

'off
 

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

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Question by:karstieman
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11 Comments
 
LVL 33

Expert Comment

by:pgnatyuk
Comment Utility
I'm not sure it will help.  It is not VB. But it is something:
http://www.hjgode.de/wp/2009/07/14/howto-run-an-application-periodically/
(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++):
http://msdn.microsoft.com/en-us/library/aa455153.aspx
Only here it looks like VB:
http://www.eggheadcafe.com/software/aspnet/29621074/why-does-this-backlight-t.aspx
 
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Author Comment

by:karstieman
Comment Utility
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 ?
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Accepted Solution

by:
pgnatyuk earned 500 total points
Comment Utility
ReleasePowerRequirement(handle from SetPower here);
 
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Author Comment

by:karstieman
Comment Utility
Thank you Pgnatyuk,

So if I'm right this should work ?

dim handle as intptr = SetPowerRequirement("BKL1:", PowerState.D0, 1, IntPtr.Zero, 0)
ReleasePowerRequirement(handle)
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Expert Comment

by:pgnatyuk
Comment Utility
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.
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LVL 5

Author Comment

by:karstieman
Comment Utility
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
ReleasePowerRequirement(handle)
MsgBox(Handle.ToInt32)  --> shows  2080980208
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Expert Comment

by:pgnatyuk
Comment Utility
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
SetSystemPowerState(NULL, POWER_STATE_ON, POWER_FORCE);

 Then a background thread with SystemIdleTimerReset():
DWORD WINAPI ThreadProc(LPVOID lpParameter)
{
 bThreadEnded=false;
 while(bRunThread){
  SystemIdleTimerReset();
  Sleep(1000);
 }
 bThreadEnded=true;
 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.
 
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Expert Comment

by:alexey_gusev
Comment Utility
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.
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Expert Comment

by:pgnatyuk
Comment Utility
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
 
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Author Comment

by:karstieman
Comment Utility
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:
ReleasePowerRequirement(handle)

Then it works.
Thanks for the help !
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Author Closing Comment

by:karstieman
Comment Utility
Thanks for the help ! It's appreciated !
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