how to respond on user drag of a column border in a listview

[vshvetsov 0]

Hi,

how can I write a respond to the event, that user has changed the width of a column in a TListView (report view) by dragging a column border with a mouse?

[Anders Melander 1782]

The column headers of a listview is in fact a separate header control owned by the listview. The column resize notifications are only sent to the parent of the header control (i.e. the listview) so in order to get at them you need to hook into the WndProc of the listview and catch the HDN_BEGINTRACK and HDN_ENDTRACK messages.

 

I'm guessing @Remy Lebeau has some code..?

[Remy Lebeau 1392]

Off the top of my head, something like this:

private
  OldListViewWndProc: TWndMethod;
  procedure MyListViewWndProc(var Message: TMessage);

...

uses
  ..., Winapi.CommCtrl, Winapi.Messages;
  
procedure TMyForm.FormCreate(Sender: TObject);
begin
  OldListViewWndProc := ListView1.WindowProc;
  ListView1.WindowProc := MyListViewWndProc;
end;

procedure TMyForm.MyListViewWndProc(var Message: TMessage);
var
  pnmhdr: PHDNotifyW;
begin
  if Message.Msg = WM_NOTIFY then
  begin
    case TWMNotify(Message).NMHdr^.code of 
      HDN_BEGINTRACKW,
      HDN_ENDTRACKW,
      HDN_TRACKW:
        pnmhdr := PHDNotifyW(TWMNotify(Message).NMHdr);
        // use pnmhdr^ fields as needed:
        // - pnmhdr^.Item is the index of the column being tracked
        // - pnmhdr^.Button is the mouse button generating the message: 0=left, 1=right, 2=middle
        // - pnmhdr^.PItem is a pointer to a THDItemW describing the changes to the tracked column
        //
        // to block changes, set Message.Result := 1 and Exit here...
    end;
  end;
  OldListViewWndProc(Message);
end;

 

[vshvetsov 0]

Thank you, @Anders Melander and @Remy Lebeau.
I dont see where I can put a mark "question is answered" or smth like that. It was useful in old forum.