我有一个银行账户计划。每个帐户可以处于初始状态或受信任帐户状态(目前)。将来可能会添加新的状态。如果处于初始状态，则不支付利息。但如果处于受信任账户状态，则支付 9% 的利息。
以下代码有效。但 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 ChangeState() 方法需要在 InitialAccountState 类中重写。
减少这种耦合的最佳 .Net 4.0 方法是什么？
状态模式
The state pattern allows a object's state to change at any given moment which actually alters its behavior.
当状态改变的顺序是预先定义的时，耦合在状态模式中不是问题。例如，交通信号灯总是从绿色-黄色-红色变化。在这种情况下，耦合不是问题——绿色确信下一步总是处于黄色状态。请参阅Analysis Of State Machine Pattern
抽象状态
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();
}
混凝土
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);
}
}
}
上下文
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);
}
}
客户端
class Program
{
static void Main(string[] args)
{
BankAccount account = new BankAccount("Jim Johnson");
account.Deposit(500.0);
account.Deposit(300.0);
account.Deposit(550.0);
account.PayInterest();
Console.ReadKey();
}
}
引用文献
最佳答案
我会将状态更改重构为另一个类，例如服务类，其职责是了解如何更改状态，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 protected 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 Controller ，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);
}
}
主要
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关注点，AccountState 类彼此解耦，现在如果您需要添加更多状态，则只需更新 1 个类。这样，AccountState 类就不需要保留状态，而只需定义行为，即如果您的帐户处于给定状态，则 Deposit 或 PayInterest 应该如何表现。您仍然可以在状态转换器类中使用规范模式。
关于c# - 减少状态模式中的耦合，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21332730/