C# 行为型模式之责任链模式

责任链模式：请求从链中的一个对象传递到下一个对象，直到请求被响应为止。通过这种方式在对象之间去除耦合。

用途：请假审批、采购审批等。

案例介绍：以公司采购东西为例子来实现责任链模式。公司规定，采购架构总价在1万之内，经理级别的人批准即可，总价大于1万小于2万5的则还需要副总进行批准，总价大于2万5小于10万的需要还需要总经理批准，而大于总价大于10万的则需要组织一个会议进行讨论

审批类： 

    /// <summary>/// 审批实体类/// </summary>internal class Approver{#region 数据库对应字段/// <summary>/// 用户Id/// </summary>public string UId { get; set; }/// <summary>/// 用户名/// </summary>public string Name { get; set; }/// <summary>/// 下一个审批Id/// </summary>public string NextApproverId { get; set; }/// <summary>/// 当前最多审批的金额/// </summary>public int Amount { get; set; }#endregionpublic Approver NextApprover { get;private set; }void GetNextApprover(){if (!string.IsNullOrWhiteSpace(NextApproverId)){// 查找数据库NextApprover = TestData.GetDataWithUId(NextApproverId);}}public virtual void ProcessRequest(PurchaseRequest request){GetNextApprover();if (request.Amount <= Amount){Console.WriteLine($"[{Name}] 批准了购买 [{request.ProductName}] 的请求");}else{if (NextApprover == null)Console.WriteLine($"需要开会讨论购买 [{request.ProductName}]");}if (NextApprover != null){NextApprover.ProcessRequest(request);}}}

 采购类：

    /// <summary>/// 采购请求/// </summary>internal class PurchaseRequest{// 金额public double Amount { get; set; }// 产品名字public string ProductName { get; set; }public PurchaseRequest(double amount, string productName){Amount = amount;ProductName = productName;}}

测试数据：

internal class TestData{static List<Approver> approvers;static TestData(){approvers = new List<Approver>(3);Approver approver1 = new Approver(){UId = Guid.NewGuid().ToString(),Name = "王总",Amount = 100000};Approver approver2 = new Approver(){UId = Guid.NewGuid().ToString(),Name = "李副总",NextApproverId = approver1.UId,Amount = 25000};Approver approver3 = new Approver(){UId = Guid.NewGuid().ToString(),Name = "孙经理",NextApproverId = approver2.UId,Amount = 10000};approvers.Add(approver1);approvers.Add(approver2);approvers.Add(approver3);}internal static List<Approver> GetDatas(){return approvers;}internal static List<Approver> GetDatas(Func<Approver, bool> func){return approvers.Where(func).ToList();}internal static Approver GetDataWithUId(string uid){return GetData((t) => t.UId == uid);}internal static Approver GetData(Func<Approver, bool> func){return approvers.FirstOrDefault(func);}}

测试用例：

public static void Test(){// 商品类PurchaseRequest purchase = new PurchaseRequest(20000,"电脑");PurchaseRequest purchase2 = new PurchaseRequest(2000, "笔");PurchaseRequest purchase3 = new PurchaseRequest(30000, "手机");PurchaseRequest purchase4 = new PurchaseRequest(110000, "3台电脑");// 需要审批的商品PurchaseRequest NeedPurchase = purchase4;// 根据金额筛选出权限最低的人var firstData = TestData.GetDatas().Where(t=>t.Amount>= NeedPurchase.Amount).OrderBy(t => t.Amount).FirstOrDefault();if (firstData == null)firstData = TestData.GetDatas().OrderByDescending(t => t.Amount).LastOrDefault();// 开始审批firstData.ProcessRequest(NeedPurchase);}