I developing a GUI in QT where I have to show the battery status icon. To get the system power status, I am using the windows API. But to show status anytime , do i need to use a thread to continuously read and display the power status?
I am thinking of using event handler. But not sure how to implement. I am thinking that for just one status icon I will run a thread. Anybody has any better suggestion, please share.
Using a thread might be a overkill, but using a timer might be much more suitable for this case.
QTimer can be used to update battery status on given interval. Just create QTimer object and connect it's timeout() signal to slot in your object, perhaps in some battery state widget. In this slot you just read the new state and update icon accordingly. Start QTimer instance with interval of your choice in milliseconds.
Btw. Qt Mobility API can be used to read power state also on desktop. Anyway if porting is not an issue, it might be easier just to use API that platform already provides.
Related
Is it possible to control (Enable/Disable) the Speaker Icon in Delphi Code.
Is there a registry entry for this?
Many Thanks...
While it might be possible to "hide" the icon by changing a undocumented registry value, the user can unhide it again in the tray icon options so this is not really a permanent solution.
If you insist on ignoring your users desire to mute their machine you can unmute the volume programmatically.
On Windows XP/2003 and older you will have to use the old mixer API. This API is not fun to deal with and you have to remember to unmute both the Wave and master volume lines. See this and this for inspiration.
Vista and later has a new COM based API that should be less painful to deal with. Create a instance of IMMDeviceEnumerator and enumerate the render endpoints (or use GetDefaultAudioEndpoint) and call IAudioEndpointVolume::SetMute on the device endpoint. This example should be pretty close, just translate it to Delphi. Volume can also be controlled per application so you might need to deal with that as well if your users are clever.
Larry Ostermans blog is also a great source for help and details about this new API.
Note: As a workaround for your unmuting, the user can simply set the volume really low to get rid of your sound. There is really no way for you to know if the sound is audible at a low volume level and setting it higher just because you can would be very evil and could really hurt somebody with headphones etc.
Is there some event or notification I can receive or hook each time an external LCD monitor is plugged in or unplugged from a laptop running Windows 7?
The laptop detects this and switches my display to the external screen and back with certain kinds of resizing or repositioning but is this exposed by the operating system so that applications can provide a handler, attach a script, etc?
If not, is there a registry setting or API I could poll from time to time?
(I prefer programming C + Win32 API)
UPDATE
Mike's answer below, WM_DEVICECHANGE led me to RegisterDeviceNotification(), but I'm struggling to implement it so far...
UPDATE 2
This question has been asked with different wording a couple of times, but not fully answered yet in my opinion:
How to detect hot plugging of monitor in a win32 application?
Getting an event on monitor hotplug for windows
According to this article Windows sends the WM_DISPLAYCHANGE message when display resolution changes and also when a display is added or removed.
If you need to react to desktop size changes due to monitor addition or removal, you can do so in the handler of this message. The LPARAM gives you the new resolution of the display on which the window is located. Notice that this resolution will be scaled if you use anything else than 100% for system DPI scaling and your program is not DPI-aware.
Alternatively use the EnumDisplayMonitors function to get the display resolution for each connected monitor and the relative positions of the monitors in the virtual desktop. This functions uses the real device pixel values regardless of DPI scaling.
You can try WM_DEVICECHANGE. If that doesn't do the trick, run your window and attach Spy++ to it which will log all the window messages it receives. Then plug your monitor in and check if you received any messages.
Alternatively you can poll GetSystemMetrics() with SM_CMONITORS.
As said here:
You will see registered messages "UxdDisplayChangeMessage" and "HotplugDetected" (second one only when adding monitor). You can use RegisterWindowMessage to get the identifier for these messages.
There are also other messages you can check, just see the linked answer.
i am using the createdesktop api to create a desktop and i would like to take a screenshot or send input mouse/keyboard without dispalying the desktop to the user.any ideeas on how to implement this???
The short answer that I've found is that you can't. You can't take a screenshot of an inactive desktop because there are no paint calls because there are no visible windows to redraw.
You can do a SwitchDesktop() call, screen shot, then SwitchDesktop() back. The user won't notice it, but you likely won't get much in the screen shot because in this short time the windows haven't had time to redraw.
Another thing is, you have to make a new thread to call SetThreadDesktop(). If you use your main thread to do so, it will fail when using a GUI application. SetThreadDesktop() fails when you have a window in the current desktop.
SysInternals has an application to manage multiple desktops (like the linux desktop switch). When your about to pick a desktop to switch to it will show you a thumbnail of the desktop. This thumbnail is not live, it is captured by the last known full redraw when the user is in that desktop. In short, if SysInternals can't do a live screenshot I doubt any of us will.
This is of course based on my own research of this exact feature. If someone has actually gotten it to work I'd love to know so I can't use it too!
Edit: This won't work for invisible desktops, I've looked to my old code, and I see that I needed that for catching screenshot of active desktop (which was not 'WinSta0\Default'), to get handle of active user desktop I've used OpenInputDesktop.
+1 ThievingSix you are right.
Sorry everyone for my misunderstanding.
You need to use SetThreadDesktop (if you are creating desktop by CreateDestkop, then you have handle for it which you pass to SetThreadDesktop). After switching desktop for thread, you can catch screenshot. Good idea would be revert to previous desktop for thread (to not 'break' other/future code).
var
lOldDesktop: HDESK;
begin
lOldDesktop:= GetThreadDesktop(GetCurrentThreadId);
try
if not SetThreadDesktop(ADesktop) then // pass handle to your desktop, or dekstop handle obtained from OpenInputDesktop
{error handle, like RaiseLastOSError or Exit(False)};
// your screenshot/input/mouse code here
finally
if lOldDesktop<> 0 then // GetThreadDesktop can fail (I don't know condition when this GetThreadDesktop(GetCurrentThreadId) could fail)
SetThreadDesktop(lOldDesktop); // revert thread to previous desktop
end;
end;
This code should run in non-main thread, as ThievingSix pointed because SetThreadDesktop can fail in that case. Safe way is spawn thread to make screenshot.
PS. I'm not sure if this will work with "send input mouse/keyboard" (it should), but for screenshot works.
Edit:
More on sessions, window stations, desktops here http://blogs.technet.com/b/askperf/archive/2007/07/24/sessions-desktops-and-windows-stations.aspx
Desktop tool (SysInternals) - http://technet.microsoft.com/en-us/sysinternals/cc817881
My program is for rendering an animation clip, but every frame has to be computed before rendered. It seems that if the computation takes seconds, windows starts to recognize my process as "not-responding" and refuses to render anything any more, although in the Task Manager, the process itself appears to switch between "running" and "not-responding" all the time.
I have been searching solutions online for a while. A lot people suggested to delete some registry entries:
HKEY_USERS.DEFAULT\Control Panel\Desktop\HungAppTimeOut
HKEY_USERS.DEFAULT\Control Panel\Desktop\WaitToKillAppTimeOut
HKEY_CURRENT_USER\Control Panel\Desktop\HungAppTimeOut
HKEY_CURRENT_USER\Control Panel\Desktop\WaitToKillAppTimeOut
HKEY_CURRENT_USER\Control Panel\Desktop\WaitToKillServiceTimeOut
But I could not find those entries. And according to the descriptions, all those entries mentioned are about controlling how long the system waits after the user requires to end a process or log off to kill a process or service. So they are not what exactly I want. I guess there must be some threshold to control when the system should start to consider one process as "not responding" and I want to change that threshold into a slightly bigger one.
Thanks for your attention and time, any suggestion is welcome!
You should avoid hanging the UI in the first place by doing your processing/computation in a background thread, rather than on the UI thread. If you're using WinForms or WPF, use a BackgroundWorker.
See here for some BGWorker examples: WPF Threads: Build More Responsive Apps With The Dispatcher
I'm using Microstation to build a model, so this is a similar process. About half way through building the model everything freezes up and adds the "application not responding" message to the title.
Disabling the Desktop Window Manager Session Manager worked for me, however in a enterprise environment this is not the best solution, as common users don't have rights to access the services panel.
Try disabling Desktop Window Manager Session Manager from services. Worked for me. That also disabled aero theme by the way. Win7 really looks fancy but it has to operate normally.
One solution that one could suggest is to periodically look for a special 'Screen-saver' desktop, and if it's present then count it as a running screensaver.
But apparently this is not the case for all screensavers as with some the mentioned desktop is always present.
Are there more reliable solutions for this?
See the WINAPI function SystemParametersInfo() with the SPI_GETSCREENSAVERRUNNING parameter. It's the only documented way to detect whether the screen saver is currently running. (You can also find out if a screen saver is even enabled, get and set the timeout value, and start the screen saver using this function.)
I think the key is to identify the screensaver by its window class ("WindowsScreenSaverClass"). I found this page
How do I start, detect and stop screen savers? that has some code examples and explanations.
HOW TO: Determine If Screen Saver Is Running by Using Visual Basic 6.0
I know this is for VB6, but it's bound to be a good place to start.
This is my implementation of screen saver event detection.
Notes:
SPI_GETSCREENSAVERRUNNING detects Windows Event id 4802 and 4803 which weren't accurate in my case, see my problem hence user idle time calculation is added
GetLastInputInfo apparently doesn't work if process is a service.
search processes for a process with .scr in its .MainModule.FileName