How to Custom Paint Node Indicators

• Jul 30, 2021

The following example demonstrates how to handle the tree list’s OnCustomDrawIndicatorCell event, used to manually paint node indicators.

In the example, a focus glyph for the focused node is painted manually as well as indicator cells.

//...
procedure <Form>.<TreeList>CustomDrawIndicatorCell(Sender: TcxCustomTreeList; ACanvas: TcxCanvas; AViewInfo: TcxTreeListIndicatorCellViewInfo; var ADone: Boolean);
var
  IndicatorKind: TcxIndicatorKind;
  // paint the indicator image (arrow)
  procedure InternalDrawIndicatorImage(ACanvas: TcxCanvas;
    const R: TRect; AKind: TcxIndicatorKind);
  var
    X, Y: Integer;
  begin
    if AKind = ikNone then Exit;
    with cxIndicatorImages, R do
    begin
      X := (Left + Right - Width) div 2;
      Y := (Top + Bottom - Height) div 2;
    end;
    // draw built-in indicator images
    cxIndicatorImages.Draw(ACanvas.Canvas, X, Y, Ord(AKind) - 1);
  end;
begin
  // specify the background color
  ACanvas.Brush.Color := $FAE6E6;
  // paint the background
  ACanvas.FillRect(AViewInfo.BoundsRect);
  if (AViewInfo.Node <> nil) and (AViewInfo.Node.Focused) then
    // the corresponding node is focused
    IndicatorKind := ikArrow
  else
    // the corresponding node is not focused
    IndicatorKind := ikNone;
  InternalDrawIndicatorImage(ACanvas, AViewInfo.BoundsRect, IndicatorKind);
  // draw a frame around the indicator cell
  ACanvas.FrameRect(AViewInfo.BoundsRect, clBlack, 1);
  // suppress the default painting
  ADone := True;
end;