Delphi 的接口(3) - 关于接口的释放

代码文件:

---

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    Button2: TButton;

    Button3: TButton;

    Button4: TButton;

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure Button3Click(Sender: TObject);

    procedure Button4Click(Sender: TObject);

  end;



  IMyInterface = interface

    procedure Proc;

  end;



  TMyClass = class(TInterfacedObject, IMyInterface)

  public

    constructor Create;

    destructor Destroy; override;

    procedure Proc;

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



constructor TMyClass.Create;

begin

  inherited;

  ShowMessage('TMyClass.Create');

end;



destructor TMyClass.Destroy;

begin

  ShowMessage('TMyClass.Destroy');

  inherited;

end;



procedure TMyClass.Proc;

begin

  ShowMessage('IMyInterface.Proc');

end;



procedure TForm1.Button1Click(Sender: TObject);

var

  c: TMyClass;

begin

  c := TMyClass.Create;

  c.Proc;

  c.Free;

  ShowMessage('**********');



{将依次显示:

   TMyClass.Create

   IMyInterface.Proc

   TMyClass.Destroy

   **********

}

end;



procedure TForm1.Button2Click(Sender: TObject);

var

  i: IMyInterface;

begin

  i := TMyClass.Create;

  i.Proc;

  ShowMessage('**********');

  //在本段程序的最后, 编译器能判断出接口不再有用, 会释放掉拥有它的类



{将依次显示:

   TMyClass.Create

   IMyInterface.Proc

   **********

   TMyClass.Destroy

}

end;



procedure TForm1.Button3Click(Sender: TObject);

var

  c: TMyClass;

  i: IMyInterface;

begin

  c := TMyClass.Create;

  i := c;

  //i := IMyInterface(c);   {也可以这样转换}

  //i := c as IMyInterface; {暂时不能使用 as, 接口拥有 GUID 后才可以使用 as 转换}

  i.Proc;

  ShowMessage('**********');



{将依次显示:

   TMyClass.Create

   IMyInterface.Proc

   **********

   TMyClass.Destroy

}

end;



procedure TForm1.Button4Click(Sender: TObject);

var

  i: IMyInterface;

begin

  i := TMyClass.Create;

  i.Proc;

  i := nil; //可以这样主动释放接口; 同时拥有它的类也会释放

  ShowMessage('**********');



{将依次显示:

   TMyClass.Create

   IMyInterface.Proc

   TMyClass.Destroy

   **********

}

end;



end.