MFC Win32 | LButtonUp not being received after clicking toolbar button (CMFCToolBarButton::OnClick) - c++

Question

What I'm trying to achieve
Well, the title might not have explained the problem very well, so here goes:
I am trying to create a Win32 app using MFC that lets you edit and inspect other windows.
I want the user to be able to select other windows.
I got inspired by the "Find Window Process" tool on the toolbar on sysinternals applications such as ProcessExplorer.
The way it works is you click, then the window disappears, and then you drag it over the window you want to select. A border pops up around it and when you let go, it selects the window the mouse is over.
My problem
The problem I was facing is that I don't know how to detect when the user lets go of the mouse on another window.
I detect mouse down using OnClick in CMFCToolBarButton
I tried using SetCapture() but that did nothing.
I tried using OnNcLButtonUp and OnLButtonUp but neither of them worked. (alongside SetCapture)
Here's my code so far (ChildView.cpp):
BEGIN_MESSAGE_MAP(CChildView, CWnd)
ON_WM_PAINT()
ON_UPDATE_COMMAND_UI(ID_TB_LOCATEWINDOW, &CChildView::EnableToolbarButton)
ON_UPDATE_COMMAND_UI(ID_TOOLS_MESSAGELAUNCHER, &CChildView::EnableToolbarButton)
ON_WM_XBUTTONUP()
// ON_WM_LBUTTONUP()
ON_WM_NCLBUTTONUP()
END_MESSAGE_MAP()
....
void CChildView::LocateWindow()
{
GetParentFrame()->ShowWindow(SW_MINIMIZE);
SetCapture();
}
void CChildView::OnNcLButtonUp(UINT nHitTest, CPoint point)
{
ReleaseCapture();
GetParentFrame()->ShowWindow(SW_NORMAL);
MessageBox(L"Stuff", L"");
CWnd::OnNcLButtonUp(nHitTest, point);
}
I want to mention that the LocateWindow function gets called when the toolbar button is clicked (as in mouse down, not mouse down AND up)
It is called from the OnClick function.
Here's the code for that:
(I replace the button with OnToolbarReset)
// CLocateWindowButton.cpp : implementation file
//
#include "pch.h"
#include "WindowHacker.h"
#include "MainFrm.h"
#include "CLocateWindowButton.h"
// CLocateWindowButton
IMPLEMENT_SERIAL(CLocateWindowButton, CMFCToolBarButton, 1)
// CLocateWindowButton member functions
CLocateWindowButton::CLocateWindowButton()
{
}
CLocateWindowButton::CLocateWindowButton(CMainFrame* mainFrame, UINT uiCmdID, LPCTSTR lpszText) : CMFCToolBarButton(uiCmdID, NULL, lpszText)
{
this->mainFrame = mainFrame;
}
BOOL CLocateWindowButton::OnClick(CWnd* pWnd, BOOL bDelay = TRUE) {
//(CMainFrame*)m_pWndParent->LocateWindow();
mainFrame->LocateWindow();
return FALSE;
}
void CLocateWindowButton::CopyFrom(const CMFCToolBarButton& src)
{
CMFCToolBarButton::CopyFrom(src);
mainFrame = ((CLocateWindowButton&)src).mainFrame;
}
//void CLocateWindowButton::AssertValid() const
//{
// CMFCToolBarButton::AssertValid();
//
// // TODO: Add your specialized code here and/or call the base class
//}
UPDATE:
It seems to work when I put it inside an LButtonDown event, it just seems to not work when it is being detected from OnClick in CMFCToolBarButton

Answer 1

I found that in CMFCToolBar::OnLButtonUp, after calling OnClick in the button, it recaptures the cursor, invalidating our SetCapture.
BUT if I return TRUE instead of FALSE in OnClick, the mouse is not recaptured.
So changing this:
BOOL CLocateWindowButton::OnClick(CWnd* pWnd, BOOL bDelay = TRUE) {
//(CMainFrame*)m_pWndParent->LocateWindow();
mainFrame->LocateWindow();
//ReleaseCapture();
this->mainFrame->SetCapture();
return FALSE;
}
To this:
BOOL CLocateWindowButton::OnClick(CWnd* pWnd, BOOL bDelay = TRUE) {
//(CMainFrame*)m_pWndParent->LocateWindow();
mainFrame->LocateWindow();
//ReleaseCapture();
this->mainFrame->SetCapture();
return TRUE; // The line is changed here
}
The message gets sent to CMainFrame instead.