Delphi 设计模式：《HeadFirst设计模式》Delphi7代码---状态模式

本文链接：https://blog.youkuaiyun.com/djCode/article/details/4794564

本文对比了使用状态模式前后的糖果机程序实现。通过具体代码展示了如何利用状态模式简化复杂的状态转换逻辑，使得代码更加清晰易维护。

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没有应用状态模式的代码

1. 工程文件

program Project1; {$APPTYPE CONSOLE} uses uGumballMachine in 'uGumballMachine.pas'; var aGumballMachine: TGumballMachine; begin aGumballMachine := TGumballMachine.Create(5); aGumballMachine.InsertQuarter; aGumballMachine.TurnCrank; Writeln; aGumballMachine.InsertQuarter; aGumballMachine.EjectQuarter; aGumballMachine.TurnCrank; Writeln; aGumballMachine.InsertQuarter; aGumballMachine.TurnCrank; aGumballMachine.InsertQuarter; aGumballMachine.TurnCrank; aGumballMachine.EjectQuarter; Writeln; aGumballMachine.InsertQuarter; aGumballMachine.InsertQuarter; aGumballMachine.TurnCrank; aGumballMachine.InsertQuarter; aGumballMachine.TurnCrank; aGumballMachine.InsertQuarter; aGumballMachine.TurnCrank; aGumballMachine.Free; Readln; end.

2.单元文件

unit uGumballMachine; interface type TGumballMachine = class(TObject) private FState: Integer; FCount: Integer; public constructor Create(aCount: Integer); procedure InsertQuarter; procedure EjectQuarter; procedure TurnCrank; procedure Dispense; end; implementation const SOLD_OUT = 0; NO_QUARTER = 1; HAS_QUARTER = 2; SOLD = 3; { TGumballMachine } constructor TGumballMachine.Create(aCount: Integer); begin FCount := aCount; FState := SOLD_OUT; if FCount > 0 then FState := NO_QUARTER; end; procedure TGumballMachine.Dispense; begin if FState = SOLD then begin Writeln('A gumball comes rolling out the slot'); FCount := FCount - 1; if FCount = 0 then begin Writeln('Oops, out of Gumballs'); FState := SOLD_OUT; end else FState := NO_QUARTER; end; if FState = NO_QUARTER then Writeln('You need to pay first'); if FState = SOLD_OUT then Writeln('No gumball dispensed'); if FState = HAS_QUARTER then Writeln('No gumball dispensed'); end; procedure TGumballMachine.EjectQuarter; begin if FState = HAS_QUARTER then begin Writeln('Quarter returned'); FState := NO_QUARTER; end; if FState = NO_QUARTER then Writeln('You haven''t inserted a quarter'); if FState = SOLD then Writeln('Sorry, you already turned the crank'); if FState = SOLD_OUT then Writeln('You can''t eject, you haven''t inserted a quarter yet'); end; procedure TGumballMachine.InsertQuarter; begin if FState = HAS_QUARTER then Writeln('You can''t insert another quarter'); if FState = NO_QUARTER then begin FState := HAS_QUARTER; Writeln('You inserted a quarter'); end; if FState = SOLD_OUT then Writeln('You can''t insert a quarter, the machine is sold out'); if FState = SOLD then Writeln('Please Wait, we''re already giving you a gumball'); end; procedure TGumballMachine.TurnCrank; begin if FState = SOLD then Writeln('Turning twice doesn''t get you another gumball'); if FState = NO_QUARTER then Writeln('You turned, but there''s no quarter'); if FState = SOLD_OUT then Writeln('You turned, but there''s no gumballs'); if FState = HAS_QUARTER then begin Writeln('You turned...'); FState := SOLD; Dispense; end; end; end.

应用状态模式的代码

1. 工程文件

2.单元文件

unit uGumballMachine; interface type TState = class; //Forward声明，创建两个相互依赖的类。 TGumballMachine = class(TObject) private FSoldOutState: TState; FNoQuarterState: TState; FHasQuarterState: TState; FSoldState: TState; FState: TState; FCount: Integer; function GetSoldOutState: TState; function GetNoQuarterState: TState; function GetHasQuarterState: TState; function GetSoldState: TState; function GetCount: Integer; public constructor Create(aNumberGumballs: Integer); destructor Destroy; override; procedure InsertQuarter; procedure EjectQuarter; procedure TurnCrank; procedure SetState(aState: TState); procedure ReleaseBall; end; TState = class(TObject) public procedure InsertQuarter; virtual; abstract; procedure EjectQuarter; virtual; abstract; procedure TurnCrank; virtual; abstract; procedure Dispense; virtual; abstract; end; TNoQuarterState = class(TState) private FGumballMachine: TGumballMachine; public constructor Create(aGumballMachine: TGumballMachine); procedure InsertQuarter; override; procedure EjectQuarter; override; procedure TurnCrank; override; procedure Dispense; override; end; THasQuarterState = class(TState) private FGumballMachine: TGumballMachine; public constructor Create(aGumballMachine: TGumballMachine); procedure InsertQuarter; override; procedure EjectQuarter; override; procedure TurnCrank; override; procedure Dispense; override; end; TSoldState = class(TState) private FGumballMachine: TGumballMachine; public constructor Create(aGumballMachine: TGumballMachine); procedure InsertQuarter; override; procedure EjectQuarter; override; procedure TurnCrank; override; procedure Dispense; override; end; TSoldOutState = class(TState) private FGumballMachine: TGumballMachine; public constructor Create(aGumballMachine: TGumballMachine); procedure InsertQuarter; override; procedure EjectQuarter; override; procedure TurnCrank; override; procedure Dispense; override; end; implementation { TNoQuarterState } constructor TNoQuarterState.Create(aGumballMachine: TGumballMachine); begin FGumballMachine := aGumballMachine; end; procedure TNoQuarterState.Dispense; begin Writeln('You needed to pay first'); end; procedure TNoQuarterState.EjectQuarter; begin Writeln('You haven''t inserted a quarter'); end; procedure TNoQuarterState.InsertQuarter; begin Writeln('You inserted a quarter'); FGumballMachine.SetState(FGumballMachine.GetHasQuarterState); end; procedure TNoQuarterState.TurnCrank; begin Writeln('You turned, but there''s no quarter'); end; { THasQuarterState } constructor THasQuarterState.Create(aGumballMachine: TGumballMachine); begin FGumballMachine := aGumballMachine; end; procedure THasQuarterState.Dispense; begin Writeln('No Gumball Dispensed'); end; procedure THasQuarterState.EjectQuarter; begin Writeln('Quarter Returned'); FGumballMachine.SetState(FGumballMachine.GetNoQuarterState); end; procedure THasQuarterState.InsertQuarter; begin Writeln('You can''t insert another quarter'); end; procedure THasQuarterState.TurnCrank; begin Writeln('You turned...'); FGumballMachine.SetState(FGumballMachine.GetSoldState); end; { TSoldState } constructor TSoldState.Create(aGumballMachine: TGumballMachine); begin FGumballMachine := aGumballMachine; end; procedure TSoldState.Dispense; begin FGumballMachine.ReleaseBall; if FGumballMachine.GetCount > 0 then FGumballMachine.SetState(FGumballMachine.GetNoQuarterState) else begin Writeln('Oop , Out of gumballs'); FGumballMachine.SetState(FGumballMachine.GetSoldOutState); end; end; procedure TSoldState.EjectQuarter; begin Writeln('Sorry, you already turned the crank'); end; procedure TSoldState.InsertQuarter; begin Writeln('Please Wait, we''re already giving you a gumball '); end; procedure TSoldState.TurnCrank; begin Writeln('Turning twice doesn''t get you another gumball'); end; { TSoldOutState } constructor TSoldOutState.Create(aGumballMachine: TGumballMachine); begin FGumballMachine := aGumballMachine; end; procedure TSoldOutState.Dispense; begin Writeln('No gumball dispensed'); end; procedure TSoldOutState.EjectQuarter; begin Writeln('You can''t eject, you haven''t inserted a quarter yet'); end; procedure TSoldOutState.InsertQuarter; begin Writeln('You can''t insert a quarter, the machine is Sold out'); end; procedure TSoldOutState.TurnCrank; begin Writeln('You turned, but there are no gumballs'); end; { TGumballMachine } constructor TGumballMachine.Create(aNumberGumballs: Integer); begin FSoldOutState := TSoldOutState.Create(Self); //var Self: TGumballMachine; FNoQuarterState := TNoQuarterState.Create(Self); FHasQuarterState := THasQuarterState.Create(Self); FSoldState := TSoldState.Create(Self); FCount := aNumberGumballs; FState := FSoldOutState; if aNumberGumballs > 0 then FState := FNoQuarterState; end; destructor TGumballMachine.Destroy; begin FSoldOutState.Free; FNoQuarterState.Free; FHasQuarterState.Free; FSoldState.Free; inherited; end; procedure TGumballMachine.EjectQuarter; begin FState.EjectQuarter; end; function TGumballMachine.GetCount: Integer; begin Result := FCount; end; function TGumballMachine.GetHasQuarterState: TState; begin Result := FHasQuarterState; end; function TGumballMachine.GetNoQuarterState: TState; begin Result := FNoQuarterState; end; function TGumballMachine.GetSoldOutState: TState; begin Result := FSoldOutState; end; function TGumballMachine.GetSoldState: TState; begin Result := FSoldState; end; procedure TGumballMachine.InsertQuarter; begin FState.InsertQuarter; end; procedure TGumballMachine.ReleaseBall; begin Writeln('A Gumball comes rolling out the slot...'); if FCount <> 0 then FCount := FCount - 1; end; procedure TGumballMachine.SetState(aState: TState); begin FState := aState; end; procedure TGumballMachine.TurnCrank; begin FState.TurnCrank; FState.Dispense; end; end.

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