理解学习Func用法

Posted 2020-08-27 幽冥狂_七

//Func用法
public static class FuncDemo{
    public static void TestFunc(){
        List<User> usList = Five.GetUserList();
        //Select是Func的委托
        //public delegate TResult Func<in T,out TResult>(T arg); //out TResult可以自定义输出类型，可以有多少输入in T
        //usList.Select(new Func<User,TResult>(delegate(User u){
            //输出参数,返回值 new Func<User,int> 这里返回int 类型
        //}));
        //返回int类型的数组
        List<int> usAges= usList.Select(new Func<User,int>(
            delegate(User u){
            return u.Age;
        })).ToList();
        //输出结果
        usAges.ForEach(u=>{Console.WriteLine(u);});
        
        //上面的缩写lambad表达式没有指定数据类型，会自行推断 (返回Age列，个人理解)
        List<int> usAges= usList.Select(u=>{
            return u.Age;
        }).ToList();
        ------------------------------------------
        //新的类型  ,Employee 是返回值
        List<Employee> els = usList.Select(new Func<User,Employee>(delegate(User u){
            Employee e = null;
            if(u.Age > 12){
                e.name = u.Name;
                e.Phone = u.Phone;
                e.Salary = 80000;
            }else{
                return null;
            }
            return e;
        })).ToList();
        
        //==========--------------begin上面缩写-----------========
         List<Employee> els = usList.Select(
         GetEmployeFromUsers //这里满足委托条件
         ).ToList();
         
         //处理els集合
         els.ForEach(e=>{
             if(e!=null)
             {
                 Console.WriteLine(e.Name+""+e.Phone);
             }
         });
    }
    
    //从新定义个方法（这里处理比较复杂，就单独写成一个方法）
    public static Employee GetEmployeFromUsers(User u){
        Employee e = new Employee();
        if(u.Age > 12){
            e.Name = u.Name;
            e.Phone = u.Phone;
            e.Salary = u.Salary;
        }else{
            return null;
        }
        return e;
    }
}

//一个实体类
public class Employee{
    public string name{get;set;}
    public string Phone{get;set;}
    public decimal Salary{get;set;}
}

//==========--------------end上面缩写-----------========