DesignPattern之SimpleFactory

unit unit2;

interface

uses
  windows, messages, sysutils, variants, classes, controls,
  dialogs, extctrls, shellapi, appevnts, forms;
type
  ifruitinterface = interface
    ['{d4557157-5241-4116-aa1e-87f86a884ea9}']
    procedure grow();
    procedure harvest();
    procedure plant();
  end;

type
  tapple = class(tcomponent, ifruitinterface)
  private
    treeage: integer;
  public
    procedure grow();
    procedure harvest();
    procedure plant();
  end;

  tstrwaberry = class(tcomponent, ifruitinterface)
  private
    treeage: integer;
  public
    procedure grow();
    procedure harvest();
    procedure plant();
  end;
  tgrape = class(tcomponent, ifruitinterface)
  private
    treeage: integer;
  public
    procedure grow();
    procedure harvest();
    procedure plant();
  end;

  tfruitgarden = class
  public
    class function getfruit(const strfruit: string): ifruitinterface;
  end;

implementation
//{$r *.dfm}
procedure tapple.grow();
begin
  showmessage('apple grow');
end;

procedure tapple.harvest();
begin
  showmessage('apple harvest');
end;

procedure tapple.plant();
begin
  showmessage('apple plant');
end;

procedure tstrwaberry.grow();
begin
  showmessage('strwaberry plant');
end;

procedure tstrwaberry.harvest();
begin
  showmessage('strwaberry plant');
end;

procedure tstrwaberry.plant();
begin
  showmessage('strwaberry plant');
end;

procedure tgrape.grow();
begin
  showmessage('grape plant');
end;

procedure tgrape.harvest();
begin
  showmessage('grape plant');
end;

procedure tgrape.plant();
begin
  showmessage('grape plant');
end;

class function tfruitgarden.getfruit(const strfruit: string): ifruitinterface;
begin
  if strfruit = 'apple' then
    result := tapple.create(nil)
  else if strfruit = 'strawberry' then
    result := tstrwaberry.create(nil)
  else if strfruit = 'grape' then
    result := tgrape.create(nil)
  else
    raise exception.create('cannot create ' + strfruit);
end;

end.

//test

  afruitgarden: tfruitgarden;
  afruit: ifruitinterface;
begin

  afruitgarden := tfruitgarden.create();
  try
    afruit := afruitgarden.getfruit(edit1.text);
    afruit.grow();
  except on fruiterror: exception do
      showmessage(fruiterror.message);
  end;

  freeandnil(afruitgarden);
end;