Handbook之007：提前声明函数

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)
    Memo1: TMemo;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure DoubleHello; forward; //forward为提前引用

procedure NewHello;
begin
  if MessageDlg(‘弹出选择对话框‘, TMsgDlgType.mtConfirmation, [TMsgDlgBtn.mbYes, TMsgDlgBtn.mbNo], 0) = mrYes then
    DoubleHello
  else
    ShowMessage(‘Hello‘);
end;

procedure DoubleHello;
begin
  NewHello;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  DoubleHello;
end;

end.