Hello,
I need to check whether backlight is on or off. How can i check?
Good question, I couldn't find a good way to tell for sure whether the backlight is on. Surely there's a bit somewhere in the low-memory globals that will tell you precisely the information you need, but I suspect you'd need to become a Palm OS licensee to get the official documentation (and support) for this bit.
I found a few ways of getting close to the info you need. :)
I know in OSes 3.5 and earlier, there is a HwrBacklight() function you could call to get the status of the backlight. I think it was an undocumented function that you just had to trap into manually with inline assembly. That API has been deprecated in newer versions of Palm OS.
There is a vchrBacklight character defined in Chars.h that appears to toggle the state of the backlight. I would imagine this key gets enqueued when the user holds down the power-on button long enough to toggle the backlight. When the OS gets ahold of this character, it calls internal routine(s) to physically toggle the backlight's state. Your app can intercept these characters in your event loop, and this will tell you when the user has toggled the backlight while your app is running. However, it won't give you any indication of the state of the backlight, so might not be of any use to you.
Other ways to get close to the information you need is to use the notification manager to determine when the device is asleep or awake. You can use SysBatteryInfo() to determine if the device is on the cradle (charging) and combine that with the state of prefStayLitWhenPluggedIn (aka stayLitWhenPluggedIn) OS preference.
Maybe somebody else on this forum has a better technique?
-Jeff Ishaq
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