I have a Windows Form Application that reads a barcode from a Web Cam.
Everything is running smooth but I still need to implement a function to the application to keep listening my keyboard inputs and be able to read the barcodes and put the reading in the clipboard.
In other words, do the stuff that my program has to do but in the background.
I searched a lot in the internet but I couldn't find any good answer to my problem.
Can you guys help me?
Thank you a lot!
There's more than one way to perform this.
So the problem is that your application doesn't have focus, and so doesn't get keyboard/mouse input passed to it. To work around that you can use Keyboard hooks.
Alternatively, you can perform polling. That is, run your 'scan' periodically - quickly enough that the user doesn't need to enter keyboard input, they just put something in front of the web cam for a second, and it scans.
You need to use a background worker to read the barcode so the main thread is not locked up. Below is a microsoft example:
http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.aspx
Related
Hello I want to press a button with my app. So I use SendKeys class
SendKeys.SendWait("{RIGHT}");
Problem is that I need to wait 3-4 seconds after this line code for reaction from system. How can I speed it up or how can I delete this delay ?
// update 1
I've also tried
SendKeys.SendWait("{RIGHT}");
SendKeys.Flush();
BUt id didn't help
// update 2
I want my app that works in background to press a button programaticly in the actual active state of the user. So if he is in excel i want the right arrow to move the active cell, if he is in the game i want to turn right etc. SendWait does the thing I want but with some delay that I don't want.
Second important thing that this is not a virus or worm or anything like that. First of all as you can see I'm too stupid for that and secondly I'm playing with my KInect so this is some kind of interaction beetwen user and computer. Thats why it works in background and thats why I need to send it to the active app of the user
SendKeys is a nice little feature for Windows Form applications. Based on your tag it appears that you're using Windows Presentation Foundation, which will not support SendKeys.Send()
https://stackoverflow.com/a/1646568/340574
Take a look at the link above to use KeyEventArgs. I've read that you could also add a reference to System.Windows.Forms.dll through Visual Studio to use SendKeys, but I have not tried it myself.
Say for example if I want to see if ms word is started but I don't want to make a timer ticking every millisecond or if the user doesn't click a button to notify like crazy. Is there some system way to do this? Like ms word starts and it sends some signal to my application? What I am trying to accomplish is actually more sophisticated but the ms word example would suffice... .net or c++/qt/mfc solutions are what I am looking for. 10x!
This article describes a method, using WMI, for receiving an event when processes are added, removed or modified:
http://weblogs.asp.net/whaggard/archive/2006/02/11/438006.aspx
It should be a simple step from this to check if it is MS word or not based on the executable name.
You can use WMI to monitor process creation:
http://weblogs.asp.net/whaggard/archive/2006/02/11/438006.aspx
This may overlap with app starting, but not exactly the same thing.
If you wanted to do something with the app once it started the .net UI Automation could also tell you when windows are created and other such events.
Alternativly, MSAA, Windows Automation, WindowHook are other APIs you might use.
How can I disable Print Screen functionality while my WPF application is running?
The use-case is that my client wants to avoid unnecessary replication of valuable patient-centric data from the outside world and they provide the physical security to keep people from taking data through non-digital means.
Okay, it is possible, and could indeed be useful if your application is deployed in an environment where a camera is not available to the user.
First of all, I used the RegisterHotKey and UnregisterHotKey API calls, documented here http://pinvoke.net/default.aspx/user32.RegisterHotKey as described in this rather old article here http://msdn.microsoft.com/en-us/magazine/cc163713.aspx.
I registered the IDHOT_SNAPDESKTOP hotkey in the Window_Load event and unregistered it in the Window_Closed. Trying to do this in the constructor gave me problems getting a consistent handle with the WindowInteropHelper(this) method.
If you'd like to do more than just ignore the keys you can set up a windows message handler, making a kind of WndProc using,
HwndSource source = HwndSource.FromHwnd(<handle>);
source.AddHook(<WndProc>);
making the handle as described above, and the WndProc implementation yourself.
As yet, I don't know how to "not" handle the hot key and get windows to perform its normal behaviour except, of course, by unregistering the hotkeys.
Its not very elegant or "WPF" but it worked for me.
As #ghord comments
The use of EnsureHandle() looks useful for getting a handler in the constructor.
It's not possible to disable printing, and even if it were possible, it would be easily circumvented by a cell phone camera. Many are in the megapixel resolution range, making it quite easy for someone to get the information they want.
If you want to disable the Print Screen Key on your keyboard, Jodrell's answer gives a way of doing that (understanding that it's not going to keep people from printing, and a determined user will find a way around that).
Really, it all comes down to trust. If an employer can't trust their employees not to remove data that is already protected by law in most jurisdictions (HIPAA in the USA), then there's a bigger issue at stake.
Easy:
Windows.UI.ViewManagement.ApplicationView.GetForCurrentView().IsScreenCaptureEnabled = false;
Simply speaking, you cannot. "Print screen" just copies the pixels on the screen to the clipboard, and is not part of your application.
Basically you can hook to the ClipBoard events and then set the image copied to null if someone does it. So they can copy the image but it will be reset:
Have a look at this:
Clipboard event C#
Alternatively in a timer, check the content of the clip board and clear it as soon as it is set to a picture.
No, No way to do that. Even if you capture the Print Screen key in your application user might set focus to some other application and then do the Print screen(having your application on side etc.).
Only way would be to create a dummy application in background which captures all keystrokes using Keyboard Hooks and filters Print Screen, but that will happen for all applications not just yours. And moreover as George said user can use cellphone camera too!
I think Microsoft Rights Management System can help. Give it a try. Following is the link:
Microsoft Rights Management System
The only way I can think of is to use the native Windows API (SetWindowsHookEx) to catch all keystrokes and filter out the PrintScreen key. However this would involve creating a native (i.e. unmanaged) DLL to actually do the keystroke processing.
I want to send an Application Key Presses, To Automate some stuff that has to be done repeatedly and So I don't always have to cramp my fingers.
In C#, it's nice to use SendKeys.Send(), but this won't work because the Application doesn't take Windows Messages. SendKeys.SendWait() does nothing at all.
How would I STILL Simulate the Keyboard events?
Come To Think of It, I was going to use some P/Invoke to simulate Mouse Events too, but If it takes no messages, How Can I get around that?
EDIT - I can use mouse and keyboard to interact with the program, I just cannot manipulate it with Windows Messages sent from my own Code.
Have you tried AutoIt?
Is it a console app? If so, maybe you should be SendKeys'ing to the command shell instance it is running in.
I have a windows form application which needs to be the TopMost. I've set my form to be the TopMost and my application works as I'd like it to except for in one case.
There is a 3rd party application (referred to as player.exe) that displays SWF movie files on a portion of the screen that popup on top of my application.
Using Process Monitor I determined that player.exe application calls
flash.exe <PositionX> <PositionY> <Width> <Height> <MovieFile>
in my case:
flash.exe 901 96 379 261 somemovie.swf
Since flash.exe is being spawned in a new process after my form has been set to the TopMost it is appearing on top of my application.
First thing I did was make my application minimize the player.exe main application window hoping that this would prevent the Flash from appearing also. But, unfortunately it doesn't... even with the window minimized whenever the flash movie starts it shows up at the pixel location (901,96). I then tried creating a timer to keep setting the form.TopMost property to true every 10ms. This sort of works but you still see a very quick blip of the swf file.
Is there some type of Windows API call which can be used to temporarily prevent player.exe from spawning child processes which are visible? I admit it sounds a little far fetched. But, curious if anyone else has had a similar problem.
Addendum:
This addendum is to provide a reply to some of the suggestions layed out in Mathew's post below.
For the emergency situation described in the comments, I would look at possible solutions along these lines:
1) How does the third party application normally get started and
stopped? Am I permitted to close it
the same way? If it is a service, the
Service Control Manager can stop it.
If it is a regular application,
sending an escape keystroke (with
SendInput() perhaps) or WM_CLOSE
message to its main window may work.
Easiest way to close the app is to CTRL-ALT-DEL, then kill process. -OR-
The proper way is to Hold ESC while clicking the left mouse button... then input your username and password, navigate some menu's to stop the player.
There is no PAUSE command... believe it or not.
I don't think using WM_CLOSE will help since minimizing the application doesn't. Would that kill the process also? If not, how do you reopen it.
2) If I can't close it nicely, am I permitted to kill it? If so,
TerminateProcess() should work.
I can't kill the process for two reasons. 1) Upon relaunch you need to supply username/password credentials... There may be a way to get around this since it doesn't prompt when the machine is rebooted but... 2) Whenever I kill the process in task manager it doesn't die gracefully and asks if you want to send an error report.
3) If I absolutely have to leave the other process running, I would try
to see if I can programmatically
invoke fast user switching to take me
to a different session (in which there
will be no competing topmost windows).
I don't know where in the API to start
with this one. (Peter Ruderman
suggests SwitchDesktop() for this
purpose in his answer.)
I got really excited by this idea... I found this article on CodeProject which provides a lot of the API Wrapper methods. I stopped implementing it because I think that in order for desktop's to work you must have explorer.exe running (which I do not).
EDIT2: On second thought... maybe explorer.exe isn't needed. I'll give it a try and report back.
Edit3: Was unable to get the code in that article working. Will have to put this on hold for a moment.
Answer Summary
As one might have expected, there is no simple answer to this problem. The best solution would be to problematically switch to a different desktop when you need to guarantee nothing will appear over it. I was unable to find a simple C# implementation of desktop switching that worked and I had a looming doubt that I would just be opening a whole new set of worms once it was implemented. Therefore, I decided not to implement the desktop switching. I did find a C++ Implementation that works well. Please post working C# virtual desktop implementations for others.
Setting the TopMost property (or adding the WS_EX_TOPMOST style to a window) does not make it unique in the system. Any number of topmost windows may be created by any number of applications; the only guarantee is that all topmost windows will be drawn 'above' all non-topmost windows. If there are two or more topmost windows, the Z-order still applies. From your description, I suspect that flash.exe is also creating a topmost window.
Aside from periodically forcing your window to the top of the Z-order, I think there is little you can do. Be warned, however, that this approach is dangerous: if two or more windows are simultaneously trying to force themselves to the top of the Z-order, the result will be a flickering mess that the user will likely have to use the task manager to escape.
I recommend that your program not attempt to meddle with other processes on the computer (unless that is its explicit purpose, e.g. a task manager clone). The computer belongs to the user, and he may not value your program more highly than all others.
Addendum:
For the emergency situation described in the comments, I would look at possible solutions along these lines:
How does the third party application normally get started and stopped? Am I permitted to close it the same way? If it is a service, the Service Control Manager can stop it. If it is a regular application, sending an escape keystroke (with SendInput() perhaps) or WM_CLOSE message to its main window may work.
If I can't close it nicely, am I permitted to kill it? If so, TerminateProcess() should work.
If I absolutely have to leave the other process running, I would try to see if I can programmatically invoke fast user switching to take me to a different session (in which there will be no competing topmost windows). I don't know where in the API to start with this one. (Peter Ruderman suggests SwitchDesktop() for this purpose in his answer.)
You can use the Process class to start flash.exe directly - and use an appropriate ProcessStartInfo settings to show the window in a hidden state - or with a WindowStyle of hidden or minimized.
You could also consider using the SetWindowsHookEx API to intercept the process start API calls, and when the process is flash.exe run some code to restore you window to top-most status.
Matthew's answer is excellent, but I suspect you may be asking the wrong question. Why does your application need to be topmost? If you're trying to create a kiosk or some such, then topmost is not the way to go.
Edit: After reading your response to Matthew's comment, I'd suggest creating a new desktop and switching to it before displaying your alert. (See CreateDesktop and SwitchDesktop in MSDN.)