设计模式循序渐进（8）职责链模式 Chain Of Responsibility

模式解说：

责任链模式是一种对象的行为模式，它将处理客户端请求的那些对象连成一条链，并沿着这条链传递请求，直到有一个对象处理它为止。其目的是使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。

UML结构图

//先看一个复杂的if语句，我已经将该语句在面向过程的范围内进行了重构，看起来好一点。

unit uAudit;

interface

type

TAudit = class(TObject)

public

procedure ProcessAudit(money: Integer);

end;

implementation

procedure TAudit.ProcessAudit(money: Integer); //处理审批

procedure ProcessByDirectorate;

begin

Writeln('500000元以上的审批，董事会处理');

end;

procedure ProcessByPresident;

begin

if money > 500000 then

ProcessByDirectorate

else

Writeln('50001-500000元的审批，总裁处理');

end;

procedure ProcessByManager;

begin

if money > 50000 then

ProcessByPresident

else

Writeln('5001-50000元的审批，经理处理');

end;

begin

if money > 5000 then

ProcessByManager

else

Writeln('5000元以下的审批，主任处理');

end;

end.

下面看看职责链的实现，并对该if进行重构

// Added by zhangsk 2008-6-9 23:09:08 使用职责链模式重构

unit uAuditChain;

interface

type

THandle = class(TObject)

private

FSuccessor: THandle;

procedure SetSuccessor(const Value: THandle);

public

property Successor: THandle read FSuccessor write SetSuccessor;

procedure HandleRequest(money: Integer); virtual; abstract;

end;

TDirectorHandle = class(THandle) //主任

public

procedure HandleRequest(money: Integer); override;

end;

TManagerHandle = class(THandle) //经理

public

procedure HandleRequest(money: Integer); override;

end;

TPresidentHandle = class(THandle) //总裁

public

procedure HandleRequest(money: Integer); override;

end;

TDirectorateHandle = class(THandle) //董事会

public

procedure HandleRequest(money: Integer); override;

end;

implementation

procedure THandle.SetSuccessor(const Value: THandle);

begin

FSuccessor := Value;

end;

procedure TDirectorHandle.HandleRequest(money: Integer);

begin

if Assigned(FSuccessor) and (money > 5000) then

FSuccessor.HandleRequest(money)

else

Writeln('5000元以下，主任处理');

end;

procedure TManagerHandle.HandleRequest(money: Integer);

begin

if Assigned(FSuccessor) and (money > 50000) then

FSuccessor.HandleRequest(money)

else

Writeln('5001-50000元，经理处理');

end;

procedure TPresidentHandle.HandleRequest(money: Integer);

begin

if Assigned(FSuccessor) and (money > 500000) then

FSuccessor.HandleRequest(money)

else

Writeln('50001-500000元，总裁处理');

end;

procedure TDirectorateHandle.HandleRequest(money: Integer);

begin

Writeln('500000元以上，董事会处理');

end;

end.

program Project1;

uses

SysUtils,

uAudit in 'uAudit.pas',

uAuditChain in 'uAuditChain.pas';

var

aAudit: TAudit;

Director: THandle;

Manager: THandle;

President: THandle;

Directorate: THandle;

begin

//使用面向过程的方法

aAudit := TAudit.Create;

aAudit.ProcessAudit(500);

aAudit.ProcessAudit(6000);

aAudit.ProcessAudit(60000);

aAudit.ProcessAudit(600000);

aAudit.Free;

//职责链重构后

Director := TDirectorHandle.Create;

Manager := TManagerHandle.Create;

President := TPresidentHandle.Create;

Directorate := TDirectorateHandle.Create;

Director.Successor := Manager;

Manager.Successor := President;

President.Successor := Directorate;

Director.HandleRequest(500);

Director.HandleRequest(6000);

Director.HandleRequest(60000);

Director.HandleRequest(600000);

Director.Free;

Manager.Free;

President.Free;

Directorate.Free;

Readln;

end.

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