How To Know When the User Clicks a Check Box in a TreeView Control (261289)

MORE INFORMATION

When the user clicks the check box of a TreeView item, an NM_CLICK notification is sent to the parent window. When this occurs, the TVM_HITTEST message returns TVHT_ONITEMSTATEICON. The TreeView control uses this same condition to toggle the state of the check box. Unfortunately, the TreeView control toggles the state after the NM_CLICK notification is sent.

You can post a user-defined message to the same window that is processing the NM_CLICK notification, and treat this user-defined message as a notification that the checked state has changed. Following is sample code that illustrates how this can be accomplished:

#define UM_CHECKSTATECHANGE (WM_USER + 100)

case WM_NOTIFY:
{
   LPNMHDR lpnmh = (LPNMHDR) lParam;
   TVHITTESTINFO ht = {0};
    
   if(lpnmh->code  == NM_CLICK) && (lpnmh->idFrom == IDC_MYTREE))
   {
      DWORD dwpos = GetMessagePos();

      // include <windowsx.h> and <windows.h> header files
      ht.pt.x = GET_X_LPARAM(dwpos);
      ht.pt.y = GET_Y_LPARAM(dwpos);
      MapWindowPoints(HWND_DESKTOP, lpnmh->hwndFrom, &ht.pt, 1);

      TreeView_HitTest(lpnmh->hwndFrom, &ht);
         
      if(TVHT_ONITEMSTATEICON & ht.flags)
      {
         
         PostMessage(hWnd, UM_CHECKSTATECHANGE, 0, (LPARAM)ht.hItem);
      }
   }
}
break;

case UM_CHECKSTATECHANGE:
   {
   HTREEITEM   hItemChanged = (HTREEITEM)lParam;
   /*
   Retrieve the new checked state of the item and handle the notification.
   */ 
   }
break;