《大话设计模式》——策略模式

抽象基类提供函数接口，不需要提供函数实现，此处区别于虚函数。

abstract class CashSuper{
	public abstract double acceptCash(double money);
}

class CashNormal:CashSuper{
	public double acceptCash(double money){
		return money;
	}
}

class CashRebate:CashSuper{
	private double moneyRebate=1d;
	
	public CashRebate(string moneyRebate){
		this.moneyRebate=double.Parse(moneyRebate);
	}
	public override double acceptCash(double money){
		return money*moneyRebate;
	}
}

class CashReturn{
	private double moneyCondition=0.0d;
	private double moneyReturn=0.0d;
	public CashReturn(string moneyCondition,string moneyReturn){
		this.moneyCondition=double.Parse(moneyCondition);
		this.moneyReturn=double.Parse(moneyReturn);
	}
	public override double acceptCash(double money){
		double result=money;
		if(money>=moneyCondition)
			result=money-Math.Floor(money/moneyCondtion)*moneyReturn;
		
		return result;
	}
}

class CashFactory{
	public static CashSuper createCashAccept(string type){
		CashSuper cs=null;
		switch(type){
			case "正常收费":
				cs=new CashNormal;
				break;
			case "满300返100":
				cs=new CashReturn("300","100");
				break;
			case "打8折":
				cs=new CashRebate("0.8");
				break;
		}
		return cs
	}
}

double total=0.0d;
private void btnOk_Click(object sender,EventArgs e){
	CashSuper csuper=CashFactory.createCashAccept(cbxType.SelectedItem.ToString());
	double totalPrices=0d;
	totalPrices=csuper.acceptCash(Convert.ToDouble(txtPrice.Text)*Convert.ToDouble(txtNum.Text));
	total=total+totalPrices;
	lbxList.Item.Add("单价:"+textPrice.Text+"数量："+txtNum.Text+" "+cbxType.SelectedItem+"合计："+totalPrices.ToString());
	lblResult.Text=total.ToString();
}

之前的CashSuper、CashNormal、CashRebate和CashReturn都不用更改，只需添加一个CashContext类，并修改客户端就好了。

class CashContext{
	private CashSuper cs;

	public CashContext(CashSuper csuper){
		this.cs=csuper;
	}

	public double GetResult(double money){
		return cs.acceptCash(money);
	}
}

double total =0.0d;
private void btnOk_Click(object sender,EventArgs e){
	CashContext cc=null;
	switch(cbxType.SelectedItem.ToString()){
		case "正常收费":
			cc=new CashContext(new CashNormal());
			break;
		case "满300返100":
			cc=new CashContext(new CashReturn("300","100"));
			break;
		case "打8折":
			cc=new CashContex(new CashRebate("0.8");
			break;
	}
	double totalPrices=0d;
	totalPrices==cc.GetResult(Convert.ToDouble(txtPrice.Text)*Convert.ToDouble(textNum.Text));
	total=total+totalPrices;
	lbxList.Items.Add("单价："+txtPrice.Text+"数量："+txtNum.Text+" "+cbxType.SelectedItem+"合计："+totalPrices.ToString());
	lblResult.Text=total.ToString();
}

class CashContext{
	CashSuper cs=null;

	public CashContext(string type){
		switch(type){
			case "正常收费":
				cs=new CashNormal();
				break;
			case "满300返100":
				cs=new CashReturn("300","100");
				break;
			case "打8折":
				cs=new CashRebate("0.8");
				break;				
		}
	}

	public double GetResult(double money){
		return cs.acceptCash(money);
	}
}

double total=0.0d;
private void btnOk_Click(object sender,EventArgs e){
	CashContext csuper=new CashContext(cbxType.SelectedItem.ToString());
	double totalPrices=0d;
	totalPrices=csuper.GetResult(Convert.ToDouble(txtPrice.Text)*Convert.ToDouble(txtNum.Text));
	total=total+totalPrices;
	lbxList.Items.Add("单价："+txtPrice.Text+"数量："+txtNum.Text+" "+cbxType.SelectedItem+"合计："+totalPrices.ToString());
	lblResult.Text=total.ToString();
}

简单工厂模式的做法，客户端需要认识两个类，CashSuper和CashFactory，而策略模式与简单工厂结合的用法，客户端只需要认识CashContext就可以了，如此耦合进一步降低。