Solved

Find handle of previous active window (win32)

Posted on 2009-07-04
3
404 Views
Last Modified: 2013-12-04
I'm trying to write a small win32 application (in C or C++)  that sends pre-cooked keystrokes to another application. The user experience should be this:

The user works with application X (which can be anything), then uses the mouse to click somewhere in the window belonging to application Y (written by me), which is visible on the screen. Application Y uses SendInput to send keystrokes to application X.

The problem is: SendInput sends keystrokes to the foreground window. How can application Y determine which window was the foreground window immediately before it received the mouse click?

Back in 1997, someone asked a similar question here (http://www.experts-exchange.com/Programming/System/Windows__Programming/Q_10010231.html), and the answer was to look at the wparam of the WM_SETFOCUS message. However,  the answer was later withdrawn (and in Vista that parameter appears to always be 0). One of the last comments on the question from 1997 says: "It seems there is no way to obtain handle of deactivated window."

Is that really true?
0
Comment
Question by:cto
3 Comments
 
LVL 9

Accepted Solution

by:
JohnGaby earned 250 total points
ID: 24776987
You might try creating a window that does not take the focus in the first place.  That way you wouldn't need to determine where the focus originated  Check out the WS_EX_NOACTIVATE style:

http://msdn.microsoft.com/en-us/library/ms632680(VS.85).aspx
0
 
LVL 86

Assisted Solution

by:jkr
jkr earned 250 total points
ID: 24776997
If we believe MSDN, it should be WM_SETFOCUS (http://msdn.microsoft.com/en-us/library/ms646283(VS.85).aspx), where it says: "wParam - Handle to the window that has lost the keyboard focus. This parameter can be NULL."

However, if that does not work for you, you might want to consider setting a global hook (see http://msdn.microsoft.com/en-us/library/ms997537.aspx - "Win32 Hooks") that filters for WM_KILLFOCUS and sends the handle of the window that message was targetted at to your app. E.g.
LRESULT CALLBACK HookProc	(	int		nCode,	// hook code

                                WPARAM	wParam,	// removal flag 

                                LPARAM  lParam 	// address of structure with message 

                            )

{

    PMSG	pmsg	=	( PMSG)	lParam;
 

    if	(	0	>	nCode	||	PM_NOREMOVE	==	wParam)	

        {

            return	(	CallNextHookEx	(	g_hhk,

                                            nCode,

                                            wParam,

                                            lParam

                                        )

                    );

        }
 

    if	(WM_KILLFOCUS == pmsg->message)

        {

            /* this one is for us, so grab the window handle here */

        }
 

    return	(	CallNextHookEx	(	g_hhk,

                                    nCode,

                                    wParam,

                                    lParam

                                )

            );

}

Open in new window

0
 

Author Comment

by:cto
ID: 24777462
Thank you, JohnGaby and jkr. Both solutions are useful, and I have split the points between you.

0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article describes a technique for converting RTF (Rich Text Format) data to HTML and provides C++ source that does it all in just a few lines of code. Although RTF is coming to be considered a "legacy" format, it is still in common use... po…
For most people, the WrapPanel seems like a magic when they switch from WinForms to WPF. Most of us will think that the code that is used to write a control like that would be difficult. However, most of the work is done by the WPF engine, and the W…
This is Part 3 in a 3-part series on Experts Exchange to discuss error handling in VBA code written for Excel. Part 1 of this series discussed basic error handling code using VBA. http://www.experts-exchange.com/videos/1478/Excel-Error-Handlin…
Windows 10 is mostly good. However the one thing that annoys me is how many clicks you have to do to dial a VPN connection. You have to go to settings from the start menu, (2 clicks), Network and Internet (1 click), Click VPN (another click) then fi…

911 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now