裝飾者模式

一.模式解說

以客戶端透明的方式動態地將責任附加到對象上.若要擴展功能,裝飾者提供了比繼承更有彈性的替代方案。裝飾者模式用意是要保持對象接口,加強對象性能.

實際生活中常常發現裝飾者模式.好比,你須要裝裱掛畫,你不想講畫和畫框定死以便更換不一樣的畫框.下圖就是一個裝裱掛畫的裝飾者模式.

裝飾者模式的使用時機:

1. 在不影響其餘對象的狀況下,動態透明的增長責任到一個對象.

2.但願責任和功能能夠隨時增長或取消.

3.當沒法經過類繼承來擴展功能時.

二.結構和用法

2.1 模式結構

 裝飾者模式結構以下圖:

包含如下參與者:

1. 抽象部件(TComonent):定義一個接口能夠動態的附加責任到其餘對象.

2.具體部件(TConcreteComponent): 定義能夠被附加責任的對象.

3.裝飾者(TDecorator): 維護一個抽象部件對象的引用,並定義與抽象部件接口一致的接口,以便裝飾抽象部件對象接口.

4.具體裝飾者(TConcreteDecorator): 附加責任到抽象部件,完成具體的裝飾.

2.2 代碼模板(Delphi)

 　　

unit Decorator;

interface

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

type
  Tcomponent = class(TObject)
  public
    procedure Operation; virtual; abstract;
  end;

  TConcreteComponent = class(Tcomponent)
  public
    procedure Operation; override;
  end;

  TDecorator = class(Tcomponent)
  private
    FComponent: TComponent;
  public
    constructor Create(Component: TComponent);
    procedure Operation;overload; override;
  end;

  TConcreteDecoratorA = class(TDecorator)
  private
    FAddedState: integer;
  public
    procedure Operation;override;
  end;

  TConcreteDecoratorB = class(TDecorator)
  public
    procedure AddedBehavior;
    procedure Operation;override;
  end;

implementation

{ TConcreteComponent }

procedure TConcreteComponent.Operation;
begin
  //被裝飾者部件的操做代碼
end;

{ TDecorator }

constructor TDecorator.Create(Component: TComponent);
begin
  FComponent := Component;
end;

procedure TDecorator.Operation;
begin
  if FComponent <> nil then
    FComponent.Operation;
end;

{ TConcreteDecoratorA }

procedure TConcreteDecoratorA.Operation;
begin
  //裝飾部件操做代碼
end;

{ TConcreteDecoratorB }

procedure TConcreteDecoratorB.AddedBehavior;
begin
  //裝飾者新增操做的代碼
end;

procedure TConcreteDecoratorB.Operation;
begin
  //裝飾部件操做代碼
  // 注意這裏是裝飾後已經擴展了對象的功能
  inherited Operation;
  AddedBehavior;
end;

end.

 2.3 問題討論

 三. 範例與實踐

3.1 裝飾者模式在圖片觀賞器中的應用

 

 

 

 部分示例代碼:

unit PicDecorator;

interface
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, ComCtrls, Jpeg;

type

  TPicShow = class(TObject)
  public
    procedure Display(Owner: TForm; ImgFile: string); virtual; abstract;
  end;

  TPic = class(TPicShow)
  public
    procedure Display(Owner: TForm; ImgFile: string); override;
  end;

  TDecoratedPic = class(TPicShow)
  private
    FComponent: TPicShow;
  public
    constructor Create(PicShow: TPicShow);
    procedure Display(Owner: TForm; ImgFile: string); overload; override;
  end;

  TPicWithFrame = class(TDecoratedPic)
  private
    FAddedFrame: integer;
  public
    procedure Display(Owner: TForm; ImgFile: string); override;
    destructor Destroy; override;
  end;

  TPicWithMusic = class(TDecoratedPic)
  public
    destructor Destroy; override;
    procedure AddMusic;
    procedure Display(Owner: TForm; ImgFile: string); override;
  end;

implementation

{ TPic }

procedure TPic.Display(Owner: TForm; ImgFile: string);
var
  Img : TImage;
begin
  Img := TImage.Create(Owner);
  Img.Picture.LoadFromFile(ImgFile);
  Img.AutoSize := True;
  Img.Stretch := True;
  Owner.Width := Img.Width + 32;
  Owner.Height := Img.Height + 64;
  Owner.Caption := ImgFile;
  Img.Left := 11;
  Img.Top := 13;
  Img.Parent := Owner;
end;

{ TDecoratedPic }

constructor TDecoratedPic.Create(PicShow: TPicShow);
begin
  Self.FComponent := PicShow;
end;

procedure TDecoratedPic.Display(Owner: TForm; ImgFile: string);
begin
  if FComponent <> nil then
    FComponent.Display(Owner, ImgFile);
end;

{ TPicWithFrame }

destructor TPicWithFrame.Destroy;
begin
  if FComponent <> nil then FComponent.Free;
end;

procedure TPicWithFrame.Display(Owner: TForm; ImgFile: string);
var
  FrmOut: TBevel;
  FrmIn: TBevel;
begin
  inherited Display(Owner, ImgFile);
  FrmIn := Tbevel.Create(Owner);
  FrmIn.Parent := Owner;
  FrmIn.Width := Owner.Width - 30;
  FrmIn.Height := Owner.Height - 62;
  FrmIn.Left := 10;
  FrmIn.Top := 12;
  FrmIn.Shape := bsBox;
  FrmIn.Style := bsLowered;

  FrmOut := Tbevel.Create(Owner);
  FrmOut.Parent := Owner;
  FrmOut.Width := Owner.Width - 18;
  FrmOut.Height := Owner.Height - 48;
  FrmOut.Left := 4;
  FrmOut.Top := 6;
  FrmOut.Shape := bsBox;
  FrmOut.Style := bsRaised;
end;

{ TPicWithMusic }

procedure TPicWithMusic.AddMusic;
begin
  SndPlaySound('SONG.wav', SND_ASYNC or SND_NODEFAULT);
end;

destructor TPicWithMusic.Destroy;
begin
  if Self.FComponent <> nil then Self.FComponent.Free;
end;

procedure TPicWithMusic.Display(Owner: TForm; ImgFile: string);
begin
  inherited Display(Owner, ImgFile);
  AddMusic;
end;

end.

四.總結