C# - 使用扩展方法排序

Question

我想对 person say 的列表进行排序

List<Person> persons=new List<Person>();
persons.Add(new Person("Jon","Bernald",45000.89));
persons.Add(new Person("Mark","Drake",346.89)); 
persons.Add(new Person("Bill","Watts",456.899));

基于

public enum CompareOptions
 {
    ByFirstName,
    ByLastName,
    BySalary
 }

 public enum SortOrder
 {
   Ascending,
   Descending
 }

使用 lambda 表达式进行排序的方法是什么？

    public static List<Person> SortPeople(this List<Person> lst, 
   CompareOptions opt1,SortOrder ord)

        {
           lst.Sort((p,op1,op2)=>{ how to apply lambda expression here});
        }

Answer 1

看起来您正试图在 List<T> 上调用 Sort 方法这需要 Comparison<T>代表。这将需要一些工作，因为您首先必须定义一个兼容的比较函数。

第一步是根据 CompareOptions 编写一个比较函数值

private static Comparison<Person> Create(CompareOptions opt) {
  switch (opt) {
    case CompareOptions.ByFirstName: (x,y) => x.FirstName.CompareTo(y.FirstName);
    case CompareOptions.ByLastName: (x,y) => x.LastName.CompareTo(y.LastName);
    case CompareOptions.BySalary: (x,y) => x.Salary - y.Salary;
    default: throw new Exception();
  }
}

默认情况下，此函数将按升序排序。如果您希望它下降，只需取反该值即可。所以现在写SortPeople可以通过下面的方式来完成

public static List<Person> SortPeople(
   this List<Person> list, 
   CompareOptions opt1,
   SortOrder ord) )
   var original = Create(opt1);
   var comp = original;
   if( ord == SortOrder.Descending ) {
     comp = (x,y) => -(orig(x,y));
   }
   list.Sort(comp);
}

编辑

100% 在 lambda 中完成的版本

public static List<Person> SortPeople(
   this List<Person> list, 
   CompareOptions opt1,
   SortOrder ord) )

   list.Sort( (x,y) => {
     int comp = 0;
     switch (opt) {
       case CompareOptions.ByFirstName: comp = x.FirstName.CompareTo(y.FirstName);
       case CompareOptions.ByLastName: comp = x.LastName.CompareTo(y.LastName);
       case CompareOptions.BySalary: comp = x.Salary.CompareTo(y.Salary);
       default: throw new Exception();
     }
     if ( ord == SortOrder.Descending ) {
       comp = -comp;
     }
     return comp;
   });
}