Winapi: Click/Press emulation button in another application.

I have handle to button in some application, that does not belong to my thread space.

I use this code:


to emulate click/keypress on this button.

However, I doubt, that it is most nice and elegant solution - is there any better?

PS: Method shouldn't involve AttachThreadInput calls, and should work on 98 and XP as well.

Who is Participating?
AlexFMConnect With a Mentor Commented:
Having any button handle you can programmatically click this button by the following way:

int nID = GetDlgCtrlID(hButton);
HWND hParent = GetParent(hButton);

if ( hParent )
    PostMessage(hParent, WM_COMMAND,  nID, hButton);
xSiGiNxAuthor Commented:
Btw code was using Delphi. Actually no difference. What I need is some sane windows message, that I could send to control (button)
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xSiGiNxAuthor Commented:
It seems close, but.. How do I use this function to send "event", if I have handle (HWND) of control?
xSiGiNxAuthor Commented:
Naw.. Not close. It seems, like it is something almost like keybd_event, which doesn't care to which control I am sending message.

And I need to send message to control directly.
xSiGiNxAuthor Commented:
Looks rather nice.. here it is translated to delphi:

procedure MyClick(Wnd,Child:HWND);

Where Wnd is Parent (Form where component is placed) and Child is Button..

It looks like it is what it should be.. But for same silly reason it doesnot just work.. =(

Perhaps its only work if AttachThreadInput is called beforehand?

Too late for me today, will test tomorrow.
Replace SendMessage with PostMessage. AttachThreadInput doesn't matter, Windows messages are always handled in the destination window thread.
Program may ignore WM_COMMAND message only if it is written by some special way - for example, handles button clicks instead of handling WM_COMMAND message. However, this way works for 99% of programs.
Using Spy++ see what message is sent to the button parent when button is clicked. Try to click button programmatically using this utility:

If you can do this using message handler, it is possible to do the same in the program. Posting the WM_COMMAND message is the simplest way, in the rare case it is not working by some reason, use SendInput as jkr writes. Having button HWND you can get it's rectangle (see GetWindowRect), move mouse cursor to some point inside of this rectangle (SetCursorPos) and make click using SendInput.
When you PostMessage to the parent, you are missing a parameter, the high word of wParam. Do this:

int nID = GetDlgCtrlID(hButton);
HWND hParent = GetParent(hButton);

if ( hParent )
    PostMessage(hParent, WM_COMMAND,
Ok, to translate that wParam to delphi (I guess...don't know that language, you'll get it :):

wParam = (NM_CLICK << 16) | nId;

Where NM_CLICK is actually 0xfffe

If defines are a problem, just:

wParam = 0xfffe0000 | (nId & 0xffff);

Where | and & are bitwise.
xSiGiNxAuthor Commented:
Still didn't work.. However, I've pinpointed problem to this point:


CtrlID.. Is same as Child. Same number. How could that be? Bug in delphi libs or I just miss something about this function?

MSDN gives me this:

"If the function succeeds, the return value is the identifier of the control.

If the function fails, the return value is zero."

adg080898Connect With a Mentor Commented:
Is it a control in a dialog box? If it is not a control in a dialog box then the concept of "control id" is optional and may not necessarily be used.

You could try injecting a WM_LBUTTONDOWN/WM_LBUTTONUP pair to see if it handles the click at that level. Forget the parent, let the control route it to its parent if that's what it does. Probably more reliable that way:

// Get center of button
RECT rectCtl;
GetClientRect(hChild, &rectCtl);
rect.left = rect.right / 2; = rect.bottom / 2;

if (hChild) {
    PostMessage(hChild, WM_LBUTTONDOWN,
            (rect.left & 0xffff) | ( << 16));
    PostMessage(hChild, WM_LBUTTONUP,
            (rect.left & 0xffff) | ( << 16));
Oops, typos. rect should be rectCtl
xSiGiNxAuthor Commented:
Thx for all replies. I am still inclined to AlexFM solution.. And it even works (Spy++ does give Control's ID - how the heck it GETS it?)

I am really curios, if it's delphi problem, so i try to rewrite call to API in inline ASM.. However - silly question:

How does calling API works in asm?

I mean if this right:

mov eax,HWND
call GetDlgCtrlId
mov CtrlID,eax

Or this:

push eax
call GetDlgCtrlId
pop eax

After I get answer, I'll finish question rewardin participants (probably raisin value)
xSiGiNxAuthor Commented:
I got it working. Thx a lot =) I omitted dialog control id at all (used 0).  
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