Question

Is it possible using the standard TTreeView to change the Expand and Collapse Image?

I don’t mean Node images, I mean the little arrows next to Nodes that have children, like so:

Ideally I would like the arrows to show as + and – Symbols, like the Delphi component structure tree:

If it is possible to change this, how would I go about doing it?

Working Demo based on David’s Answer

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ComCtrls, Themes, uxTheme;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

type
  TMyTreeView = class(TTreeView)
  protected
    procedure CreateWnd; override;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TMyTreeView }

procedure TMyTreeView.CreateWnd;
begin
  inherited;
  if ThemeServices.Enabled and CheckWin32Version(6, 0) then
    SetWindowTheme(Handle, nil, nil);
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  MyTree: TMyTreeView;
  Node: TTreeNode;
begin
  MyTree := TMyTreeView.Create(nil);
  with MyTree do
  begin
    Parent  := Self;
    Height  := 100;
    Width   := 100;
    Left    := 30;
    Top     := 30;

    Node := Items.Add(nil, 'Item');
    Items.AddChild(Node, 'Item');
    Node := Items.AddChild(Node, 'Item');
    Items.AddChild(Node, 'Item');
  end;
end;

end.

The Result:

Answer 1

Tree views in post-Vista Windows have two alternative themes. The theme that you are wanting to avoid is known as the explorer theme. You want to use the standard theme. A control has to opt-in to get the explorer theme. It does so via the SetWindowTheme API. The VCL tree view control calls this to opt-in. It does so at the end of its CreateWnd method.

You can revert to the standard theme by undoing the change like this:

type
  TMyTreeView = class(TTreeView)
  protected
    procedure CreateWnd; override;
  end;

procedure TMyTreeView.CreateWnd;
begin
  inherited;
  if StyleServices.Enabled and TOSVersion.Check(6) and StyleServices.IsSystemStyle then
    SetWindowTheme(Handle, nil, nil);
end;

This code is written for XE2. If you have an earlier Delphi then I think you want it like this:

  if ThemeServices.Enabled and CheckWin32Version(6, 0) then
    SetWindowTheme(Handle, nil, nil);