Delphi 設計模式：《HeadFirst設計模式》---行為模式之責任鏈模式

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模式解說  責任鏈模式是一種對象的行為模式，它將處理用戶端請求的那些對象聯成一條鏈，並沿著這條鏈傳遞請求，直到有一個對象處理它為止。通常使用在以下場合  1 有多個對象可以處理一個請求，哪個對象處理該請求事先並不知道，而是在運行時自動確定；  2 希望在不明確制定接收者的情況下，向多個對象中的一個提交請求；  3 處理一個請求的對象集合需要動態指定時；16.2 結構和用法  1．抽象處理者(THandler)－定義了一個處理請求的介面。如果需要，則聲明一個方法，實現對後續對象的連結；  2．具體處理者(TConcreteHandler)－負責處理求；連結後續對象，如果它能處理該請求，則處理，如果不能，則傳遞給其連結化物件處理；  3．用戶端（TClient）－發出請求給責任鏈中的具體處理對象；程式碼範例：unit Chain;interfacetype  THandler = class  private    FSuccessor: THandler;    procedure SetSuccessor(const Value: THandler);  public    procedure HandleRequest; virtual; abstract;    property Successor: THandler read FSuccessor write SetSuccessor;  end;  TConcreteHandler1 = class(THandler)  public    procedure HandleRequest; override;  end;  TConcreteHandler2 = class(THandler)  public    procedure HandleRequest; override;  end;implementationuses Dialogs;{ Thandler }procedure THandler.SetSuccessor(const Value: THandler);begin  FSuccessor := Value;end;{ TConcreteHandler2 }procedure TConcreteHandler2.HandleRequest;begin  inherited;  if Successor <> nil then  begin    ShowMessage(self.ClassName +  ‘將請求傳遞到 ‘ +  Successor.ClassName);    Successor.HandleRequest;  end  else  begin    ShowMessage(self.ClassName + ‘ 處理了請求！‘);  end;end;{ TConcreteHandler1 }procedure TConcreteHandler1.HandleRequest;begin  inherited;  if Successor <> nil then  begin    ShowMessage(self.ClassName +  ‘將請求傳遞到 ‘ +  Successor.ClassName);    Successor.HandleRequest;  end  else  begin    ShowMessage(self.ClassName + ‘ 處理了請求！‘);  end;end;end.用戶端代碼unit Main;interfaceuses  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,  Dialogs, StdCtrls;type  TForm1 = class(TForm)    OtherDone: TButton;    SelfDone: TButton;    procedure OtherDoneClick(Sender: TObject);    procedure SelfDoneClick(Sender: TObject);  private    { Private declarations }  public    { Public declarations }  end;var  Form1: TForm1;implementationuses Chain;{$R *.dfm}procedure TForm1.OtherDoneClick(Sender: TObject);var  Handler1, Handler2: THandler;begin  Handler1 := TConcreteHandler1.Create;  Handler2 := TConcreteHandler1.Create;  try    Handler1.Successor := Handler2;    Handler1.HandleRequest;  finally    Handler1.Free;    Handler2.Free;  end;end;procedure TForm1.SelfDoneClick(Sender: TObject);var  Handler1, Handler2: THandler;begin  Handler1 := TConcreteHandler1.Create;  Handler2 := TConcreteHandler1.Create;  try    Handler1.HandleRequest;  finally    Handler1.Free;    Handler2.Free;  end;end;end.

Delphi 設計模式：《HeadFirst設計模式》---行為模式之責任鏈模式