How to do loop -> until keypressed

Set the Form's property KeyPreview as True (It will allow it to receive Pressed Keys before controlls placed on it):

unit Unit_Q_20963045;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Buttons;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    SpeedButton1: TSpeedButton;
    procedure FormCreate(Sender: TObject);
    procedure FormKeyPress(Sender: TObject; var Key: Char);
    procedure SpeedButton1Click(Sender: TObject);
  private{ Private declarations }
    PressedKey: Char;
  public { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  PressedKey := #0;
end;

procedure TForm1.FormKeyPress(Sender: TObject; var Key: Char);
begin
  PressedKey := Key;
end;

procedure TForm1.SpeedButton1Click(Sender: TObject);
begin
  try
    repeat
      Memo1.SetFocus;
      Memo1.Lines.add('Hello!') ;
      Application.ProcessMessages;
    until (PressedKey=#27);
  finally
    PressedKey := #0;
  end;
end;

end.

//.............................

object Form1: TForm1
  Left = 216
  Top = 114
  Width = 696
  Height = 480
  Caption = 'Form1'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  KeyPreview = True
  OldCreateOrder = False
  OnCreate = FormCreate
  OnKeyPress = FormKeyPress
  PixelsPerInch = 96
  TextHeight = 13
  object SpeedButton1: TSpeedButton
    Left = 52
    Top = 76
    Width = 135
    Height = 22
    Caption = 'Check Key Press'
    OnClick = SpeedButton1Click
  end
  object Memo1: TMemo
    Left = 286
    Top = 42
    Width = 255
    Height = 317
    TabOrder = 0
  end
end

Most easy and primitive variant:


unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Timer1: TTimer;
    Button1: TButton;
    procedure Timer1Timer(Sender: TObject);
    procedure FormKeyPress(Sender: TObject; var Key: Char);
    procedure Memo1KeyPress(Sender: TObject; var Key: Char);
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Timer1Timer(Sender: TObject);
begin
Memo1.Lines.Add('Hello!')
end;

procedure TForm1.FormKeyPress(Sender: TObject; var Key: Char);
begin
Timer1.Enabled:=false;
 Button1.Enabled:=true;
end;

procedure TForm1.Memo1KeyPress(Sender: TObject; var Key: Char);
begin
Timer1.Enabled:=false;
 Button1.Enabled:=true;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
Timer1.Enabled :=true;
 Button1.Enabled:=false;
end;


end.