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== Code Samples ==
=== Greeting Message Generator === '''[http://matrix.senecac.on.ca/~rmwang/btppresentation/sunsample.html Click here to see the UML diagram for this example]''' '''State class interface definition'''<pre>class CBaseState{public: virtual CBaseState* GetNextState() = 0; virtual char* ToString() = 0;};</pre>'''Concrete class definitions'''<pre> class CMorning : public CBaseState{public: virtual CBaseState* GetNextState(); virtual char* ToString();};class CEvening : public CBaseState{public: virtual CBaseState* GetNextState(); virtual char* ToString();}; class CNight: public CBaseState{public: virtual CBaseState* GetNextState(); virtual char* ToString();};</pre>'''Context class structure'''<pre>class CSun{public: CSun(); CSun(CBaseState* pContext); ~CSun(); void StateChanged(); char* GetStateName();protected: void DoCleanUp(); CBaseState* m_pState;};</pre>'''Function definition for state change'''<pre>void CSun::StateChanged(){ if (m_pState){ CBaseState* pState = m_pState->GetNextState(); delete m_pState; m_pState = pState; }}</pre>'''Code that changes state'''<pre>CBaseState* CMorning::GetNextState(){return new CEvening;}CBaseState* CEvening::GetNextState(){return new CNight;}CBaseState* CNight::GetNextState(){return new CMorning;}</pre>'''Simple example of actual implementation'''<pre>CSun objSun(new CMorning);printf("\n\nSun Says Good %s !!!",objSun.GetStateName());objSun.StateChanged();printf("\n\nSun Says Good %s !!!",objSun.GetStateName());objSun.StateChanged();printf("\n\nSun Says Good %s !!!",objSun.GetStateName());objSun.StateChanged(); printf("\n\nSun Says Good %s !!!",objSun.GetStateName());</pre> === Game programming: Character Status ==='''[http://matrix.senecac.on.ca/~rmwang/btppresentation/statesample.html Click here to see the UML diagram for this example]''' <br />'''Header File Content'''
<pre>
class IState;
};
</pre>
'''Class Definitions for State objects'''
<pre>
class IState {
void Operate();
};
</pre>
'''Functions that changes character status'''
<pre>
cDarkElf::cDarkElf() {_pState = new cState_Stop;}
}
void cDarkElf::Stop() { ChangeState(new cState_Stop);}
void cDarkElf::HoldPosition() {
}
void cDarkElf::Update() { _pState->Operate();} </pre> === State Pattern Example: C# ==='''Abstract Class'''<pre>using System;using System.Drawing; namespace StatePatternApp{ public abstract class State { public State() { } public State(State state) { this.CurrentLevel = state.CurrentLevel; this.Deviation = state.Deviation; this.MaxLevel = state.MaxLevel; this.MinLevel = state.MinLevel; this.Machine = state.Machine; this.SetParams(); } public State(Machine machine, int iCurrentLevel, int iDeviation, int iMaxLevel, int iMinLevel) { this.CurrentLevel = iCurrentLevel; this.Deviation = iDeviation; this.MaxLevel = iMaxLevel; this.MinLevel = iMinLevel; this.Machine = machine; this.SetParams(); } private Machine machine; private int minLevel = 0; private int maxLevel = 0; private int currentLevel = 0; private int deviation = 0; private Color messageColor = Color.Green; private string messageText = ""; public virtual void SetParams(){} public virtual void CheckEfficiency() { Transition t = Transition.GetInstance(); t.Transform(this); } protected virtual void ChangeState(Machine m, State s) { m.ChangeState(s); } public Machine Machine { get { return this.machine; } set { this.machine = value; } } public int MinLevel { get { return this.minLevel; } set { this.minLevel = value; } } public int MaxLevel { get { return this.maxLevel; } set { this.maxLevel = value; } } public int CurrentLevel { get { return this.currentLevel; } set { this.currentLevel = value; // Is the machine value set? if(this.Machine != null) { this.CheckEfficiency(); } } } public int Deviation { get { return this.deviation; } set { this.deviation = value; } } public int MaxDeviaton { get { return this.MaxLevel - this.Deviation; } } public int MinDeviaton { get { return this.MinLevel + this.Deviation; } } public Color MessageColor { get { return this.messageColor; } set { this.messageColor = value; } } public string MessageText { get { return this.messageText; } set { this.messageText = value; } } }}
</pre>
'''Transition class'''
<PRE>
using System;
namespace StatePatternApp
{
class Transition
{
private static Transition getInstance;
protected Transition() {}
public static Transition GetInstance()
{
if(getInstance == null)
{
getInstance = new Transition();
}
return getInstance;
}
public void Transform(State state)
{
if(state == null)
{
return;
}
// Get the type of state.
string stateType = state.GetType().Name;
// Are we in normal state?
if(state.CurrentLevel < state.MaxDeviaton &&
state.CurrentLevel > state.MinDeviaton)
{
if(stateType.ToUpper() != "NORMALSTATE")
{
state.ChangeState(state.Machine,
new NormalState(state));
}
}
// Are we in warning?
if(state.Deviation > 0)
{
if((state.CurrentLevel < state.MaxLevel &&
state.CurrentLevel >= state.MaxDeviaton) ||
state.CurrentLevel > state.MinLevel &&
state.CurrentLevel <= state.MinDeviaton)
{
if(stateType.ToUpper() != "WARNINGSTATE")
{
state.ChangeState(state.Machine,
new WarningState(state));
}
}
}
// Are we in alert state?
if(state.CurrentLevel >= state.MaxLevel ||
state.CurrentLevel <= state.MinLevel)
{
if(stateType.ToUpper() != "ALERTSTATE")
{
state.ChangeState(state.Machine,
new AlertState(state));
}
}
}
}
}
</PRE>
'''NormalState - derived state class'''
<PRE>using System;
using System.Drawing;
namespace StatePatternApp
{
public class NormalState : State
{
public NormalState(State state) : base(state)
{
}
public NormalState(Machine machine, int iCurrentLevel,
int iDeviation, int iMaxLevel, int iMinLevel) :
base(machine, iCurrentLevel, iDeviation,
iMaxLevel, iMinLevel)
{
}
public override void SetParams()
{
this.MessageColor = Color.Green;
this.MessageText = "Normal";
}
}
}</PRE>
'''WarningState - derived state class'''
<PRE>using System;
using System.Drawing;
namespace StatePatternApp
{
public class WarningState : State
{
public WarningState(State state) : base(state)
{
}
public WarningState(Machine machine, int iCurrentLevel,
int iDeviation, int iMaxLevel, int iMinLevel) :
base(machine, iCurrentLevel, iDeviation, iMaxLevel,
iMinLevel)
{
}
public override void SetParams()
{
this.MessageColor = Color.Yellow;
this.MessageText = "Warning";
}
}
}</PRE>
'''AlertState - derived state class'''
<PRE>using System;
using System.Drawing;
namespace StatePatternApp
{
public class AlertState : State
{
public AlertState(State state) : base(state)
{
}
public AlertState(Machine machine, int iCurrentLevel,
int iDeviation, int iMaxLevel, int iMinLevel) :
base(machine, iCurrentLevel, iDeviation, iMaxLevel,
iMinLevel)
{
}
public override void SetParams()
{
this.MessageColor = Color.Red;
this.MessageText = "Alert";
}
}
}</PRE>
'''Machine class - This class maintains an instance of state'''
<PRE lang=cs id=pre5 style="MARGIN-TOP: 0px">using System;
namespace StatePatternApp
{
public class Machine
{
public State currentState;
public Machine(int iCurrentLevel, int iDeviation,
int iMaxLevel, int iMinLevel)
{
currentState = new NormalState(this, iCurrentLevel,
iDeviation, iMaxLevel, iMinLevel);
currentState.CheckEfficiency();
}
public void ChangeState(State setState)
{
currentState = setState;
}
== References ==
<li>Erich, Gamma. Design Patterns : elements of reusable object-oriented software. Upper Saddle River: Pearson Education Corporate Sales Division, 2000.</li>
<li>"4th Lecture about Design Patterns". Ssamdark's Homepage. March 20, 2007 <http://www.misofruit.co.kr/seojewoo/programming/designpattern4.htm>.
</li>
<li>Young, Kenny. "C# - State Pattern Example". The Code Project. April 2nd, 2007 <http://www.codeproject.com/cs/design/statepatterncsharp.asp>.
</li>
</ul>
