大话设计模式之策略模式

Strategy(策略)模式：定义了一个算法家族，分别封装起来，这些算法之间可以互相切换，此模式让算法的变化，不会影响到使用算法的客户。简而言之，策略模式封装了变化，此变化即为算法。使用场合为：在不同的时候要使用不同的业务规则，可以考虑使用策略模式处理这种变化的可能性。

本文以超市收银软件为说明蓝图：

业务逻辑规则：

abstract class CashSuper

    {

        public abstract double acceptCash(double money);

    }



class CashNormal:CashSuper

    {

        public override double acceptCash(double money)

        {

            return money;

        }

    }



class CashReturn:CashSuper

    {

        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 / moneyCondition) * moneyReturn;

            return result;

        }

    }



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 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);

        }

    }

View Code

客户端：

double total = 0.0d;

        private void Form1_Load(object sender, EventArgs e)

        {

            cbxType.Items.AddRange(new object[] { "正常收费","满300返100", "打8折"});

            cbxType.SelectedIndex = 0;

        }



        private void btnOk_Click(object sender, EventArgs e)

        {

            string type = cbxType.SelectedItem.ToString();

            CashContext cc = new CashContext(type);

            double totalPrices = cc.getResult(Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text));

            total += totalPrices;

            lbxList.Items.Add("单价: " + txtPrice.Text + " 数量: " + txtNum.Text + " " + cbxType.SelectedItem + " 合计：" + totalPrices.ToString());

            lblResult.Text = total.ToString();

        }



        private void btnReset_Click(object sender, EventArgs e)

        {

            txtPrice.Text = "";

            txtNum.Text = "";

            cbxType.SelectedIndex = 0;

            lblResult.Text = "";

            lbxList.Items.Clear();

        }

View Code