我有一个银行帐户计划。每个帐户可以处于初始状态或可信帐户状态（目前）。在未来可能会添加新的州。如果处于初始状态，则不支付利息。但如果它处于可信帐户状态，则支付9％的利息。
以下代码有效。但是ChangeState（）方法中存在紧密耦合。 InitialAccountState需要知道TrustedAccountedState的存在。如果我们添加一个名为VeteranAccountedState的新状态，则需要在{{1}中重写ChangeState（）方法} class。
什么是最好的.Net 4.0减少这种耦合的方法？
状态模式
状态模式允许对象的状态在任何给定时刻发生变化，实际上会改变其行为。
当预先定义状态变化的顺序时，耦合在状态模式中不是问题。例如，交通信号灯将始终从绿色 - 黄色 - 红色变为红色。在这种情况下，耦合不是问题 - 格林确信在下一步中它始终是黄色状态。请参阅Analysis Of State Machine Pattern
摘要状态
InitialAccountState混凝土
abstract class AccountState
{
// Properties
public BankAccount Account { get; set; }
public double Balance { get; set; }
protected double interest;
protected double lowerLimit;
protected double upperLimit;
public abstract void Deposit(double amount);
public abstract void PayInterest();
}
CONTEXT
class InitialAccountState : AccountState
{
public InitialAccountState(AccountState state) :this(state.Balance, state.Account)
{
}
public InitialAccountState(double balance, BankAccount account)
{
this.Balance = balance;
this.Account = account;
Initialize();
}
private void Initialize()
{
lowerLimit = 0.0;
upperLimit = 1000.0;
}
public override void Deposit(double amount)
{
Balance += amount;
ChangeState();
}
public override void PayInterest()
{
throw new Exception("No Interest Allowed");
}
private void ChangeState()
{
if (Balance > upperLimit)
{
Account.State = new TrustedAccountedState(this);
}
}
}
class TrustedAccountedState : AccountState
{
public TrustedAccountedState(AccountState state): this(state.Balance, state.Account)
{
}
public TrustedAccountedState(double balance, BankAccount account)
{
this.Balance = balance;
this.Account = account;
Initialize();
}
private void Initialize()
{
interest = 0.05;
lowerLimit = 1000.0;
upperLimit = 10000000.0;
}
public override void Deposit(double amount)
{
Balance += amount;
ChangeState();
}
public override void PayInterest()
{
Balance += interest * Balance;
ChangeState();
}
private void ChangeState()
{
if (Balance < lowerLimit)
{
Account.State = new InitialAccountState(this);
}
}
}
客户端
class BankAccount
{
// Properties
public AccountState State { get; set; }
public double Balance
{
get { return State.Balance; }
}
// Constructor
public BankAccount(string owner)
{
this.State = new InitialAccountState(0.0, this);
}
public void Deposit(double amount)
{
State.Deposit(amount);
Console.WriteLine("Deposited {0:C} --- ", amount);
Console.WriteLine(" Balance = {0:C}", this.Balance);
Console.WriteLine(" Status = {0}", this.State.GetType().Name);
Console.WriteLine("");
}
public void PayInterest()
{
State.PayInterest();
Console.WriteLine("INTEREST PAID --- ");
Console.WriteLine(" Balance = {0:C}", this.Balance);
Console.WriteLine(" Status = {0}\n", this.State.GetType().Name);
}
}
参考
答案 0 :(得分：4)
我会重构将状态更改为另一个类，如服务类，其职责是理解如何更改状态从而反转依赖关系并消除状态之间的紧密耦合。 所以我会更改抽象类，以便可以访问受保护的属性。
abstract class AccountState
{
// Properties
public BankAccount Account { get; set; }
public double Balance { get; set; }
internal double interest;
internal double lowerLimit;
internal double upperLimit;
public abstract void Deposit(double amount);
public abstract void PayInterest();
}
添加StateChanger类...
public class StateChanger(){
public AccountState ChangeState(AccountState state){
if((state is InitialAccountState) && (state.Balance > state.upperLimit)){
return new TrustedAccountedState(state);
}
if((state is TrustedAccountedState) && (state.Balance < state.lowerLimit))
{
return new InitialAccountState(state);
}
return state;
}
}
从AccountState类中删除依赖项
class InitialAccountState : AccountState
{
public InitialAccountState(AccountState state) :this(state.Balance, state.Account)
{
}
public InitialAccountState(double balance, BankAccount account)
{
this.Balance = balance;
this.Account = account;
Initialize();
}
private void Initialize()
{
lowerLimit = 0.0;
upperLimit = 1000.0;
}
public override void Deposit(double amount)
{
Balance += amount;
}
public override void PayInterest()
{
throw new Exception("No Interest Allowed");
}
}
class TrustedAccountedState : AccountState
{
public TrustedAccountedState(AccountState state): this(state.Balance, state.Account)
{
}
public TrustedAccountedState(double balance, BankAccount account)
{
this.Balance = balance;
this.Account = account;
Initialize();
}
private void Initialize()
{
interest = 0.05;
lowerLimit = 1000.0;
upperLimit = 10000000.0;
}
public override void Deposit(double amount)
{
Balance += amount;
}
public override void PayInterest()
{
Balance += interest * Balance;
}
}
然后你的BackAccount类就像一个控制器，它看起来像
class BankAccount
{
// Properties
public AccountState State { get; set; }
private StateChanger stateChanger;
public double Balance
{
get { return State.Balance; }
}
// Constructor
public BankAccount(string owner,StateChanger stateChanger)
{
this.State = new InitialAccountState(0.0, this);
this.stateChanger = stateChanger;
}
public void Deposit(double amount)
{
State.Deposit(amount);
State = stateChanger.ChangeState(State);
Console.WriteLine("Deposited {0:C} --- ", amount);
Console.WriteLine(" Balance = {0:C}", this.Balance);
Console.WriteLine(" Status = {0}", this.State.GetType().Name);
Console.WriteLine("");
}
public void PayInterest()
{
State.PayInterest();
State = stateChanger.ChangeState(State);
Console.WriteLine("INTEREST PAID --- ");
Console.WriteLine(" Balance = {0:C}", this.Balance);
Console.WriteLine(" Status = {0}\n", this.State.GetType().Name);
}
}
和主
class Program
{
static void Main(string[] args)
{
StateChanger stateChanger = new StateChanger();
BankAccount account = new BankAccount("Jim Johnson",stateChanger);
account.Deposit(500.0);
account.Deposit(300.0);
account.Deposit(550.0);
account.PayInterest();
Console.ReadKey();
}
}
通过分离管理状态的问题，AccountState类彼此分离，现在如果需要添加更多状态，则只需要更新一个类。然后，AccountState类不需要保持状态，而只是定义行为，即如果您的帐户处于给定状态，存款或PayInterest应如何表现。您仍然可以在statechanger类中使用规范模式。