Handling tree control check box selection/de-selection in Win32/MFC

// CTreeCtrl *m_fileTreeCtrl is a member of CDemoTreeDlg dialog.

// CDemoTreeDlg dialog will handle the TVN_KEYDOWN and NM_CLICK messages

BEGIN_MESSAGE_MAP(CDemoTreeDlg, CDialog)

      ON_MESSAGE(TREE_VIEW_CHECK_STATE_CHANGE, OnTreeViewCheckStateChange)

      ON_NOTIFY(NM_CLICK, IDC_FILESYS_TREE, &CDemoTreeDlg::OnNMClickFileSysTree)

      ON_NOTIFY(TVN_KEYDOWN, IDC_FILESYS_TREE, &CDemoTreeDlg::OnTvnKeydownFileSysTree)

END_MESSAGE_MAP()

// handle mouse click on check box

void CDemoTreeDlg::OnNMClickFileSysTree(NMHDR *pNMHDR, LRESULT *pResult)

{

      // TODO: Add your control notification handler code here

      HTREEITEM item;

      UINT flags;

      // verify that we have a mouse click in the check box area

      DWORD pos = GetMessagePos();

      CPoint point(LOWORD(pos), HIWORD(pos));

      m_fileTreeCtrl->ScreenToClient(&point);

      item = m_fileTreeCtrl->HitTest(point, &flags);

      if(item && (flags & TVHT_ONITEMSTATEICON))

      {

            // handle state change here or post message to another handler

            // Post message state has changed…

            // PostMessage(TREE_VIEW_CHECK_STATE_CHANGE,0,(LPARAM)item);

      }

      *pResult = 0;

}

// handle key press on check box

void CDemoTreeDlg::OnTvnKeydownFileSysTree(NMHDR *pNMHDR, LRESULT *pResult)

{

      LPNMTVKEYDOWN pTVKeyDown = reinterpret_cast<LPNMTVKEYDOWN>(pNMHDR);

      // TODO: Add your control notification handler code here

      // we only want to handle the space key press

      if(pTVKeyDown->wVKey==VK_SPACE)

      {

            // Determine the selected tree item.

            HTREEITEM item = m_fileTreeCtrl->GetSelectedItem();

            if(item!=NULL)

            {

                  // handle state change here or post message to another handler

                  // Post message state has changed…

                  // PostMessage(TREE_VIEW_CHECK_STATE_CHANGE,0,(LPARAM)item);

            }

      }

      *pResult = 0;

}

In many cases it is better to handle the check box change in a central place after the change. To do this we can define a custom message that will be called when a check box state has changed:

// define a custom message

#define TREE_VIEW_CHECK_STATE_CHANGE (WM_USER + 100)

// implementation for TREE_VIEW_CHECK_STATE_CHANGE message handler

LRESULT CDemoTreeDlg::OnTreeViewCheckStateChange(WPARAM wParam, LPARAM lParam)

{

      // Handle message here…

      HTREEITEM   changedItem = (HTREEITEM)lParam;

      int checkState = m_fileTreeCtrl->GetCheck(changedItem);

      // Do something with check state change information…

}