unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes,
  Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, Vcl.StdCtrls,
  Vcl.ComCtrls;

type
  TForm1 = class(TForm)
    TreeView1: TTreeView;
    Button1: TButton;
    Panel1: TPanel;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private 宣言 }
  public
    { Public 宣言 }
  end;

var
  Form1: TForm1;

implementation

uses
  Winapi.CommCtrl;

{$R *.dfm}

//=============================================================================
//  フォーム生成時の処理
//  テスト用のデータをセット
//=============================================================================
procedure TForm1.FormCreate(Sender: TObject);
var
  LText1 : string;
  LText2 : string;
  LNode1 : TTreeNode;
  LIidx  : Integer;
  LJidx  : Integer;
begin
  TreeView1.Items.BeginUpdate;

  for LIIdx := 0 to 2 do begin
    LText1 := 'Item' + Format('%.2d',[LIIdx + 1]);
    LNode1 := TreeView1.Items.Add(nil, LText1);
    for LJidx := 0 to 2 do begin
      LText2 := LText1 + '-' + Format('%.3d',[LJidx + 1]);
      TreeView1.Items.AddChild(LNode1, LText2);
    end;
  end;

  TreeView1.Items.EndUpdate;

  Button1Click(nil);
end;

//=============================================================================
//  TreeView1 の行の高さの設定と取得
//  uses に Winapi.CommCtrl が必要
//=============================================================================
procedure TForm1.Button1Click(Sender: TObject);
{$WRITEABLECONST ON}
const
  LItemHeight : Integer = 10;
{$WRITEABLECONST OFF}
var
  LHeight : Integer;
begin
  if TreeView1.Items.Count < 1 then Exit;

  if Sender <> nil then begin
   // 行の高さを変更して，次の高さの値を 2 ピクセル増やす
   TreeView_SetItemHeight(TreeView1.Handle, LItemHeight);
   Inc(LItemHeight, 2);
 end;

 // 行の高さを取得して表示
 LHeight := TreeView_GetItemHeight(TreeView1.Handle);
 Panel1.Caption := 'ItemHeight : ' + IntToStr(LHeight);
end;

end.