Keep your Smartphone backlight on

If your application involves displaying screen content you probably have come across the issue where the screen backlight turns off after a few seconds of no keypresses. You can override this behaviour in your application using a couple of underdocumented API Power-Management functions. Here is a VB.NET snippet for .NETCF to keep the backlight on:-


Namespace OpenNETCF.WindowsCE.Forms


 


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


End Namespace


Thanks to Paul O’Brien from MoDaCo for inspiring and helping test the code.

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