我想排列一个人的名单
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表达方式进行排序是什么？
public static List<Person> SortPeople(this List<Person> lst,CompareOptions opt1,SortOrder ord)
{
lst.Sort((p,op1,op2)=>{ how to apply lambda expression here});
}
解决方法
看起来您正在尝试调用List< T>中的Sort方法.其采用比较< T>代表.这将需要一些工作,因为您首先必须定义兼容的比较功能.
第一步是根据CompareOptions值写一个比较函数
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,此功能将按升序排序.如果你希望它下降,就简单地否定这个值.所以现在编写SortPeople可以通过以下方式完成
public static List<Person> SortPeople(
this List<Person> list,SortOrder ord) )
var original = Create(opt1);
var comp = original;
if( ord == SortOrder.Descending ) {
comp = (x,y) => -(orig(x,y));
}
list.Sort(comp);
}
编辑
在lambda中完成100％的版本
public static List<Person> SortPeople(
this List<Person> list,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;
});
}
