一、說明

委托Predicate 可以有參數（比如下面的示例），也可以不帶參數，委托Predicate是返回固定值bool值的委托

二、示例代碼（控制臺程序）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Learn1
{
    class Program
    {
        static void Main(string[] args)
        {
            
 
int ageState = 1;
            int claState = 1;
            int age = 10;
            string className = "1班";
            List<Student> myList = new List<Student>() { 
            new Student(){ age=1, className="2班", name="同學1"},
            new Student(){ age=2, className="1班", name="
 
同學2"},
            new Student(){ age=12, className="3班", name="同學3"},
            new Student(){ age=6, className="3班", name="同學4"},
            new Student(){ age=14, className="1班", name="同學5"},
            new Student(){ age=18, className="1班", name="同學6"},
            new Student(){ age=7, className="
 
1班", name="同學7"},
          new Student(){ age=15, className="2班", name="同學8"},
            new Student(){ age=19, className="2班", name="同學9"},
            new Student(){ age=25, className="1班", name="同學10"},
            new Student(){ age=32, className="1班", name="同學11"},
            new Student(){ age=16, className="1班", name="同學12"},
            new Student(){ age=1, className="2班", name="同學13"}
            
            };
            List<Student> resultList = myList.FindAll(new Predicate<Student>(
                delegate(Student stu)
                {
                    bool IsOk = true;
                    if (ageState==1)
                    {
                    if(stu.age<age)
                    {
                        IsOk = false;
                    }
                    }

                    if(claState==1)
                    {
                    if(stu.className!=className)
                    {
                        IsOk = false;
                    }
                    }

                    return IsOk;
                
                }
                
                ));
            resultList.ForEach(x => {
                Console.WriteLine("名稱:{0},年齡:{1},班級:{2}",x.name,x.age,x.className);
            });
            Console.ReadKey();
        }
    }
    public class Student
    {
        public string name { get; set; }
        public string className { get; set; }
        public int age { get; set; }
    }
}

c# 委托 Predicate的使用示例