Delphi的接口（3） - 关于接口的释放

Delphi的接口（3） - 关于接口的释放2012-12-12 博客园万一代码文件:
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.