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Re: Globally intercepting keyboard events and blocking them if required

7-Jul-05 8:39

Hello!

I have an old notebook with no display (don’t ask - long story). Now I want to put it back in use by developing a Text-to-Speech-based menu, e.g. I press ‘m’ and the program outputs something like “You are in the main menu. Press 1 to do …., press 2 to do ….., …” via TTS – all just for fun. The TTS part isn’t much of a problem but I was wondering if I could reassign keys like the windows key. Essentially, I would like to globally (before Windows does) intercept any keyboard events and then pass them directly to an application of my choice or simply drop them.
Am I looking for a hook? Or do they, as I’ve read, only allow for monitoring system events but not altering or discarding them all together?
If I’m wrong with that assumption I would appreciate any help concerning hooks and especially their interop side. I’ve read that global hooks require the code to reside in a DLL? I guess this doesn’t include managed DLLs and I would have to do it in unmanaged C++.
If I’m right I’m open to any suggestions and any useful resources you can provide.
Thanks in advance.

Regards,
Florian

Dave Kreskowiak7-Jul-05 9:54

Re: Globally intercepting keyboard events and blocking them if required

7-Jul-05 9:54

I've done something kind of similar to what your thinking of. I did it in C++ though. I found it much easier than trying to Interop the thing. You'll also be able to rebuild/customize keyboard messages easier too. If you want to eat a keyboard message, it's easy enough. You just don't pass it up the hook chain when you're done processing it, if any.

Global, low-level hooks, can be in an .EXE and still work. The latest example I used of this was to eat any Windows key message. (This effectively disables hitting Windows-E and starting Explorer, even though Group Policy disabled running it!)

You're only problem, that I see, is going to be maintaining control of focus while you send keyboard messages around.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Florian Albrechtskirchinger8-Jul-05 2:57

Re: Globally intercepting keyboard events and blocking them if required

8-Jul-05 2:57

Thank you so far.
I haven't been programming C++ for 2 years now so I would prefer doing as much as possible in C#.
I guess I could write a C++ DLL and then wrapp it with some managed code.
I think I'm going to read a few MSDN articles about hooks.

Dave Kreskowiak8-Jul-05 3:55

Re: Globally intercepting keyboard events and blocking them if required

8-Jul-05 3:55

I didn't say it couldn't be done entirely in C#, I just said I found it easier to do in C++. If you wanted to, you could write the thing in Managed C++ so it's easier to build an interface to your C# app.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Florian Albrechtskirchinger9-Jul-05 4:30

Re: Globally intercepting keyboard events and blocking them if required

9-Jul-05 4:30

I found an interesting article on .NET 247 (http://www.dotnet247.com/247reference/msgs/26/134226.aspx) and rewrote the code to match the new C++ syntax introduced with .NET 2.0.

#pragma once
#include <windows.h>
#undef MessageBox
#using <system.dll>
#using <system.windows.forms.dll>
using namespace System;
using namespace System::Windows::Forms;
using namespace System::Reflection;
using namespace System::Runtime::InteropServices;

#pragma data_seg(".Share")
HHOOK g_Hook = 0;
#pragma data_seg()
#pragma comment(linker, "/section:.Share,rws")

namespace Hooks
{
	int __stdcall KeyboardProc(int code, int wparam, int lparam)
	{
		String^ text = String::Concat("You pressed : ", ((Keys)wparam).ToString());
		MessageBox::Show(text, "Hook Message", MessageBoxButtons::OK);
		return CallNextHookEx(g_Hook, code, wparam, lparam);
		return 0;
	}

	public ref class KeyboardHook
	{
	private:
		KeyboardHook() {};
	public:
		static void SetHook() {
			if (g_Hook != 0)
				return;
			Module^ mod = Assembly::GetExecutingAssembly()->GetModule("Hooks.dll");
			IntPtr hinst = Marshal::GetHINSTANCE(mod);
			g_Hook = SetWindowsHookEx(WH_KEYBOARD, reinterpret_cast<HOOKPROC>(KeyboardProc), static_cast<HINSTANCE>(hinst.ToPointer()), 0);
		}
		static void Unhook() {
			if (g_Hook != 0) {
				UnhookWindowsHookEx(g_Hook);
				g_Hook = 0;
			}
		}
	};
};

At first I don’t understand exactly why the g_Hook variable is declared after #pragma data_seg(“.Share”).

Besides this I need a more flexible way to integrate it into C# so I declared a managed class KeyboardHookEventArgs and a delegate KeyboardHookDelegate which I wanted to pass in from C#.
The delegate should then be called and pass all information about the keyboard event in my C# app.
The problem is I can’t invoke the delegate from inside the HOOKPROC callback because the delegate is managed but the callback is not (__stdcall).
Another issue: How do I check that the callback variable is assigned? In C# I would check if the variable is null but in C++, using NULL, I get the error that my delegate type can’t be implicitly casted to int.

Here the code for the KeyboardHookEventArgs and the delegate:

public ref class KeyboardHookEventArgs
{
private:
	bool block;
	int code;
	int wParam;
	int lParam;

public:
	property bool Block
	{
		bool get()
		{
			return block;
		}
		void set(bool value)
		{
			block = value;
		}
	}

	property int Code
	{
		int get()
		{
			return code;
		}

		void set(int value)
		{
			code = value;
		}
	}

	property int WParam
	{
		int get()
		{
			return wParam;
		}

		void set(int value)
		{
			wParam = value;
		}
	}

	property int LParam
	{
		int get()
		{
			return lParam;
		}

		void set(int value)
		{
			lParam = value;
		}
	}

	KeyboardHookEventArgs()
	{
		block = false;
		code = 0;
		wParam = 0;
		lParam = 0;
	}
	
	KeyboardHookEventArgs(int code, int wParam, int lParam)
	{
		this->code = code;
		this->wParam = wParam;
		this->lParam = lParam;
		this->block = false;
	}

	KeyboardHookEventArgs(int code, int wParam, int lParam, bool block)
	{
		this->code = code;
		this->wParam = wParam;
		this->lParam = lParam;
		this->block = block;
	}
};

public delegate void KeyboardHookDelegate(KeyboardHookEventArgs^ e);

The Block property in the event args is used to determine wether the event should or should not be passed on.

I’m really stuck here and hope somebody can give me some hints.

Florian Albrechtskirchinger13-Jul-05 7:43

Is Someone aware of this Error?

13-Jul-05 7:43

Thanks to a great article (Calling Managed Code from Unmanaged Code and vice-versa[^]) I'm down to one question which is about pinning delegates on the CLR heap and actually belongs in the Managed C++ board (How to prevent a delegate from relocating on the CLR heap[^]).

TimeSpans as Int's?

YawgmothIII7-Jul-05 5:48

YawgmothIII

7-Jul-05 5:48

Ok i need to know how to figure out how many milliseconds have passed over a period of time. I do this with two... "time stamps" - dtmCurrent & dtmPrevious - I then just subtract (dtmCurrent-dtmPrevious) and i get a TimeSpan. How do i convert that TimeSpan into an int? I need that int to be how many milliseconds have passed in that TimeSpan, though.

Of course if there is a better way to do this... without a timer... then i'm all up for suggestions. Big Grin | :-D

Here's a snipet of my code thats used.

bool FirstRun = true;<br />
		DateTime dtmCurrent;<br />
		DateTime dtmPrevious;<br />
<br />
		private void MainGame()<br />
		{<br />
			if (FirstRun == true)<br />
			{<br />
				this.ObjectEngine.Create_Unit(1,0,1,400,400,0);<br />
				FirstRun = false;<br />
				dtmCurrent = DateTime.Now;<br />
			}<br />
			dtmPrevious = dtmCurrent;<br />
			dtmCurrent = DateTime.Now;<br />
			<br />
			for (int i=0; i<ObjectEngine.ActiveUnitQPt; i++)<br />
			{<br />
				Sprite_Update((dtmCurrent - dtmPrevious), i);<br />
			}<br />
			SpriteEngine.Draw();<br />
		}

Re: TimeSpans as Int's?

leppie7-Jul-05 6:00

leppie

7-Jul-05 6:00

TimeSpan.TotalMilliseconds

^{xacc-ide 0.0.15 now with C#, MSIL, C, XML, ASP.NET, Nemerle, MyXaml and HLSL coloring - Screenshots}

just4ulove77-Jul-05 5:45

7-Jul-05 5:45

Hi..
I am getting this Error while DateTime.Parse(txtActStartDate.ToString())
where the textbox contains - 31-01-2004 -- in dd-MM-yyyy format

The string was not recognized as a valid DateTime. There is a unknown word starting at index 0.

Whats the problem?
Thanks

Alomgir Miah7-Jul-05 5:57

Alomgir Miah

7-Jul-05 5:57

Please use the overloaded Parse method

DateTime.Parse Method (String, IFormatProvider, DateTimeStyles)

and specify the Format.

just4ulove77-Jul-05 7:48

7-Jul-05 7:48

I used .. Convert.ToDateTime("31/01/2004",new CultureInfo("en-GB"))

But still getting the same error, I want to specify British Date Style..

???

Thanks

Guffa7-Jul-05 7:55

Guffa

7-Jul-05 7:55

It works just fine when I try it.

Does your code look exactly like that?

---
b { font-weight: normal; }

just4ulove77-Jul-05 7:59

7-Jul-05 7:59

Hi,
I have set the date value in the text box. I am trying to save in this way...
Convert.ToDateTime(txtname.Text,new CultureInfo("en-GB")).. txtname contains 31/03/2004
This is throwing the same error.
But again I hard-code the value of txtname.text with
Convert.ToDateTime("31/03/2004",new CultureInfo("en-GB"))
Its working fine..

What cud be the problem with the textbox?

Thanks

Guffa7-Jul-05 8:20

Guffa

7-Jul-05 8:20

Have you tried to write out the value from the text box, so that you are sure that it is sent to the server correctly?

---
b { font-weight: normal; }

Dave Kreskowiak7-Jul-05 8:02

7-Jul-05 8:02

That's because your using the Convert class. Use the DateTime Parse method to do this:

DateTime newDate = DateTime.Parse("31/01/2004", new CultureInfo("en-GB"));

DateTime newDate = DateTime.Parse("31/01/2004", "dd/MM/yyyy", Application.CurrentCulture.DateTimeFormat);

also works.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

just4ulove77-Jul-05 8:06

7-Jul-05 8:06

Thanks a lot, its working fine..

But wats the diff between Convert and DateTime class for this. It was working with a hardcoded string and not with a textbox?

Dave Kreskowiak7-Jul-05 9:45

7-Jul-05 9:45

When you're converting a string to any kind of object, if the object has a Parse method, use it. IMHO, it's always going to work better than the more generic methods in Convert. Also, Parse deals with whitespace and invalid character issues better. I've almost gotten away with never using Convert in any of my apps...

There is no difference between a TextBox's Text property and a String. The Text property returns a String object, so, the only possible problem is an input error in the TextBox. If you include leading and/or trailing spaces, tabs, incorrect formatting characters, ..., Convert might not work whereas Parse might.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome