码农公寓

命令模式可以很轻松的实现撤销（Undo）功能。

命令的接受者：

 1unit uReceiveObject;
 2
 3interface
 4
 5type
 6  TLight = class(TObject)
 7  public
 8    procedure Open;
 9    procedure Off;
10  end;
11
12implementation
13
14{ TLight }
15
16procedure TLight.Off;
17begin
18  Writeln(‘Light is off.‘);
19end;
20
21procedure TLight.Open;
22begin
23  Writeln(‘Light is on.‘);
24end;
25
26end.
27

 

命令对象：

 1unit uCommandObject;
 2
 3interface
 4
 5uses
 6  uReceiveObject;
 7
 8type
 9  TCommand = class(TObject)
10  public
11    procedure Execute; virtual; abstract;
12    procedure Undo;    virtual; abstract;
13  end;
14
15  TLightOnCommand = class(TCommand)
16  private
17    FLight: TLight;
18  public
19    constructor Create(aLight: TLight);
20    procedure Execute; override;
21    procedure Undo;    override;
22  end;
23
24  TLightOffCommand = class(TCommand)
25  private
26    FLight: TLight;
27  public
28    constructor Create(aLight: TLight);
29    procedure Execute; override;
30    procedure Undo;    override;
31  end;
32
33implementation
34
35{ TLightOnCommand }
36
37constructor TLightOnCommand.Create(aLight: TLight);
38begin
39  FLight := aLight;
40end;
41
42procedure TLightOnCommand.Execute;
43begin
44  FLight.Open;
45end;
46
47procedure TLightOnCommand.Undo;
48begin
49  FLight.Off;
50end;
51
52{ TLightOffCommand }
53
54constructor TLightOffCommand.Create(aLight: TLight);
55begin
56  FLight := aLight;
57end;
58
59procedure TLightOffCommand.Execute;
60begin
61  FLight.Off;
62end;
63
64procedure TLightOffCommand.Undo;
65begin
66  FLight.Open;
67end;
68
69end.
70

 

命令的请求者：

 1unit uSimpleRemoteWithUndo;
 2
 3interface
 4
 5uses
 6  uCommandObject;
 7
 8type
 9  TSimpleRemoteWithUndo = class(TObject)
10  private
11    FOnCommand  : TCommand;
12    FOffCommand : TCommand;
13    FUndoCommand: TCommand;
14  public
15    procedure SetCommand(aOnCommand, aOffCommand: TCommand);
16    procedure OnButtonWasPressed;
17    procedure OffButtonWasPressed;
18    procedure UndoButtonWasPressed;
19  end;  
20
21implementation
22
23{ TSimpleRemoteWithUndo }
24
25procedure TSimpleRemoteWithUndo.OffButtonWasPressed;
26begin
27  FOffCommand.Execute;
28  FUndoCommand := FOffCommand;
29end;
30
31procedure TSimpleRemoteWithUndo.OnButtonWasPressed;
32begin
33  FOnCommand.Execute;
34  FUndoCommand := FOnCommand;
35end;
36
37procedure TSimpleRemoteWithUndo.SetCommand(aOnCommand, aOffCommand: TCommand);
38begin
39  FOnCommand  := aOnCommand;
40  FOffCommand := aOffCommand;
41end;
42
43procedure TSimpleRemoteWithUndo.UndoButtonWasPressed;
44begin
45  FUndoCommand.Undo;
46end;
47
48end.
49

 

客户端，创建具体的命令对象：

 1program pSimpleRemoteWithUndoTest;
 2
 3{$APPTYPE CONSOLE}
 4
 5uses
 6  uSimpleRemoteWithUndo in ‘uSimpleRemoteWithUndo.pas‘,
 7  uCommandObject in ‘uCommandObject.pas‘,
 8  uReceiveObject in ‘uReceiveObject.pas‘;
 9
10var
11  Remote: TSimpleRemoteWithUndo;
12  Light : TLight;
13  LightOnCommand : TCommand;
14  LightOffCommand: TCommand;
15  
16begin
17  Remote := TSimpleRemoteWithUndo.Create;
18
19  Light  := TLight.Create;
20
21  LightOnCommand  := TLightOnCommand.Create(Light);
22  LightOffCommand := TLightOffCommand.Create(Light);
23
24  Remote.SetCommand(LightOnCommand, LightOffCommand);
25
26  Remote.OnButtonWasPressed;
27  Remote.OffButtonWasPressed;
28  Remote.UndoButtonWasPressed;
29  Writeln;
30  Remote.OffButtonWasPressed;
31  Remote.OnButtonWasPressed;
32  Remote.UndoButtonWasPressed;
33
34  Remote.Free;
35  Light.Free;
36  LightOnCommand.Free;
37  LightOffCommand.Free;
38  
39  Readln;
40end.
41

 

运行结果：