(WinAPI) Simulating item selection in ComboBox - c++

Question

I am currently writing a wrapper for an existing application that has its own GUI. I don't have access to original application's source code (unfortunately). The program that I am writing is in C++ and I am making use of WinAPI. I am manipulating target application by simulating button-clocks, ticking checkboxes etc.
The problem I am facing at the moment is following:
I need to make a selection in droplist implemented as WinAPI ComboBox. I am doing it by using macro ComboBox_SetCurSel. The selection in the droplist changes correctly. However in the original application there is a read-only textbox that changes the value depending on the selection in combobox. And this one does not change when I execute ComboBox_SetCurSel.
The assumption I made is that CBN_SELENDOK and/or CBN_SELCHANGE are sent when selecting an entry in ComboBox manually and this is the bit I am not doing when setting the selection with ComboBox_SetCurSel macro.
However due to lack of experience I cannot figure out how to resolve the problem. Who is normally listening for CBN_SELENDOK and CBN_SELCHANGE. Is it main application window, parent element of the combobox or main application thread? How do I find out.
Is there a macro that would do the whole thing? Like changing the selected item in ComboBox and sending all necessary notifications? Is there some smart workaround?
Any help on the subject, or any additional questions that would help to make situation more clear are welcome.
UPDATE: thanks for comment by Jonathan Potter. I am now attempting to send messages explicitly. Here is the part of the code where I am doing it:
int res = ComboBox_SetCurSel(this->handle, index);
if (res == CB_ERR)
{
return false;
}
PostMessage(GetParent(this->handle),WM_COMMAND, MAKEWPARAM(0,CBN_SELENDOK),0);
PostMessage(GetParent(this->handle),WM_COMMAND, MAKEWPARAM(0,CBN_SELCHANGE),0);
Note this->handle is just a handle to ComboBox itself as I have packed it into the structure for convenience. GetParent(this->handle) Should get immediate parent of ComboBox
Still no result. Does the order of messages matter? Also how do I obtain the identifier that needs to go into LOWORD of WPARAM sent along with WM_COMMAND?
ANSWER:
Thanks to AlwaysLearningNewStuff I have found and an answer. I have been sending messages with 0 as LPARAM. Apparently a handle to ComboBox itself neets to be sent as LPARAM in order for solution to work. This would take me ages to figure it out.
#AlwaysLearningNewStuff, you should have posted this as an answer, not a comment.
Also the bit about using GetDlgCtrlID() to get ControlID of the ComboBox is very useful. This makes code more reliable.
Thank you, everyone who participated.
Here is my final code:
if (this->handle == NULL)
{
return false;
}
int res = ComboBox_SetCurSel(this->handle, index);
if (res == CB_ERR)
{
return false;
}
PostMessage(GetParent(this->handle), WM_COMMAND, MAKEWPARAM(GetDlgCtrlID( this->handle ),CBN_SELENDOK),
(LPARAM)(this->handle));
PostMessage(GetParent(this->handle), WM_COMMAND, MAKEWPARAM(GetDlgCtrlID( this->handle ),CBN_SELCHANGE),
(LPARAM)(this->handle));
return true;

Answer 1

You are correct that CBN_SELCHANGE is not sent when using ComboBox_SetCurSel(), and the documentation says as much:
The CBN_SELCHANGE notification code is not sent when the current selection is set using the CB_SETCURSEL message.
So you have to send the notifications manually. However, you are missing key elements in your messages - the ComboBox's Control ID and HWND. The parent window uses those to identify which child control is sending messages to it so it can then act accordingly.
Try this instead:
int res = ComboBox_SetCurSel(this->handle, index);
if (res == CB_ERR)
{
return false;
}
HWND hParent = GetParent(this->handle);
int iCtrlId = GetDlgCtrlID(this->handle);
if (GetWindowLong(this->handle, GWL_STYLE) & CBS_SIMPLE)
PostMessage(hParent, WM_COMMAND, MAKEWPARAM(iCtrlId,CBN_SELENDOK), LPARAM(this->handle));
PostMessage(hParent, WM_COMMAND, MAKEWPARAM(iCtrlId,CBN_SELCHANGE), LPARAM(this->handle));