How to get notified when the user clicks the header column check box in VirtualTreeView control?

Question

Is there an event notifying about the VirtualTreeView header column check box click? It is the check box highlighted on this picture:

Answer 1

Write a handler for the OnHeaderClick event and check if the HitPosition property of the HitInfo parameter contains the hhiOnCheckbox flag. For example:

procedure TForm1.VirtualTreeHeaderClick(Sender: TVTHeader; HitInfo: TVTHeaderHitInfo);
begin
  if hhiOnCheckbox in HitInfo.HitPosition then
  begin
    if Sender.Columns[HitInfo.Column].CheckState = csCheckedNormal then
      ShowMessage('Checked!')
    else
      ShowMessage('Unchecked!')
  end;
end;