unit Unit1;

interface

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

type
  // 父接口
  IGreetable = interface
    [‘{FE5A34E5-21AB-4120-971B-FDC3241AD55D}‘]
    // 用于返回一段文本
    function SayHello: string;
  end;

  TMan = class(TObject, IGreetable)
    function SayHello: string;
    // 接口都会有的3个函数(QueryInterface，_AddRef，_Release)
    function QueryInterface(const IID: TGUID; out Obj): HResult; stdcall;
    function _AddRef: Integer; stdcall;
    function _Release: Integer; stdcall;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    // 弹出一段文本
    procedure Greeting(Intf: IGreetable);
    {Private declarations}
  public
    {Public declarations}
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

// 这里实现自己定义的_AddRef、_Release和QueryInterface方法

// 用于查找接口
function TMan.QueryInterface(const IID: TGUID; out Obj): HResult;
begin
  // 找到返回0，找不到返回‘No such interface supported‘
  if GetInterface(IID, Obj) then
    Result := 0
  else
    Result := Windows.E_NoInterface;
end;

// 接口调用计数
function TMan._AddRef: Integer;
begin
  Result := -1
end;

// 接口释放计数
function TMan._Release: Integer;
begin
  Result := -1
end;

// 客户函数，返回一段文本
function TMan.SayHello: string;
begin
  Result := ‘Hello‘;
end;

procedure TForm1.Greeting(Intf: IGreetable);
begin
  // 输出一段话
  ShowMessage(Intf.SayHello);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  // 定义一个父接口
  Intf: IGreetable;
begin
  // 子接口创建
  Intf := TMan.Create;
  // 调用的是子接口中的Greeting函数
  Greeting(Intf);
end;

end.