unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  TTest = class
    procedure Test;
    constructor Create;
    destructor Destroy; override;
    procedure CallHandler(Sender: TObject);
  private
    FOnTest: TNotifyEvent;
  public
    Tick: Integer;
    TestStr: string;
    TestArr: TArray<Integer>;

    property OnTest: TNotifyEvent read FOnTest write FOnTest;
  end;

var
  Form1: TForm1;
  Test1: TTest;

implementation

{$R *.dfm}

procedure TestCallBack(Test1: TTest);
begin
  Test1.OnTest(Test1);
end;

procedure TTest.CallHandler(Sender: TObject);
var
  cl: TTest;
begin
  cl := TTest(Sender);

  for VAR I := Low(cl.TestArr) to High(cl.TestArr) do
  begin
    Tick := (cl.TestArr[I] * 2) - TestArr[I];
  end;
  TestStr := TestStr + Tick.ToString;
end;

procedure TTest.Test;
begin
  TestCallBack(self);
end;

constructor TTest.Create;
begin
  Tick := 0;
  OnTest := CallHandler;

  SetLength(TestArr, Random(100));
  for var I := Low(TestArr) to High(TestArr) do
    TestArr[I] := I * 2;

  TestStr := 'Count := ' + Length(TestArr).ToString;
end;

destructor TTest.Destroy;
begin
  Test;
  ShowMessage(TestStr);
  SetLength(TestArr, 0);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Try
    FreeAndNil(Test1);
  Except
    on E: Exception do
      ShowMessage(E.ClassName + ' ошибка с сообщением : ' + E.Message);
  end;

  if Test1 = nil then
    ShowMessage('Обнулён');
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Test1 := TTest.Create;
end;

end.