Mega Code Archive
Creating an equivalent to the missing TListView.OnColumnDblClick
<![CDATA[
Title: Creating an equivalent to the missing TListView.OnColumnDblClick
Question: 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 ); { 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).
Bogdan Grigorescu - BogdanG@gmail.com
BG Remote Programming Group
]]>