Creating an equivalent to the missing TListView.OnColumnDblClick (Views: 28)
Problem/Question/Abstract: How to subclass your header-control (using a TListView), to receive a OnColumnDblClick- equivalent notification? Answer: This requires a bit of work. MS did not see fit to send a notification to the TListView when the user double-clicks on the header. But the header control class does have the CS_DBLCLKS style, so it does get WM_LBUTTONDBLCLK messages, it just does not do anything with them. To get at these messages requires API-style subclassing of the header control. How? See below. uses..., Commctrl; ... const UM_LISTVIEW_COLUMN_DBLCLICK = WM_USER + 1982; .... { the HeaderProc function should look something like this: } function HeaderProc(wnd: HWND; msg: Cardinal; wparam: WPARAM; lparam: LPARAM): Longint; stdcall; var hti: THDHitTestInfo; begin Result := CallWindowProc(Pointer(GetWindowLong(wnd, GWL_USERDATA)), wnd, msg, wparam, lparam); if msg = WM_LBUTTONDBLCLK then begin FillChar(hti, sizeof(hti), 0); hti.Point := SmallPointToPoint(TSmallPoint(lparam)); if SendMessage(wnd, HDM_HITTEST, 0, Longint(@hti)) >= 0 then if hti.Flags = HHT_ONHEADER then PostMessage(MainForm.Handle, UM_LISTVIEW_COLUMN_DBLCLICK, hti.Item, 0); { Change MainForm to whatever you need } end; end; procedure TMainForm.FormCreate(Sender: TObject); var wnd: HWND; oldProc: Integer; begin {beginning of workaround for missing TListView.OnColumnDblClick} wnd := GetWindow(aListView.handle, GW_CHILD); { <-- your TListView's name here } if wnd <> 0 then begin if (GetClassLong(wnd, GCL_STYLE) and CS_DBLCLKS) <> 0 then begin oldproc := GetWIndowLong(wnd, GWL_WNDPROC); if GetWindowLong(wnd, GWL_USERDATA) <> 0 then raise Exception.Create('Cannot sublcass ListView header, USERDATA already in use'); SetWIndowLong(wnd, GWL_USERDATA, oldproc); SetWindowLong(wnd, GWL_WNDPROC, integer(@HeaderProc)); end; end else ShowMessage('ListView component in vsReport state is missing !!!'); {...} {Do some more wonderful things} end; and then don't forget to declare a custom message handler for UM_LISTVIEW_COLUMN_DBLCLICK (this will be your OnColumnDblClick equivalent). |