C#學習Predicate

C#學習Predicate

using System;
using System.Reflection;
using System.Collections.Generic;
using System.Drawing;
namespace Predicate
{
    /// <summary>
    /// Represents the method that defines a set of criteria and determines whether the specified object meets
    /// those criteria
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
            // The following example uses a Predicate<T> delegate with the Array.Find method to search an array of
            // Pointer structures.The example explicitly defines a Predicate<T> delagate named predicate and assigns
            // it a method named FindPoints that return true if the product of Point.X and Point.Y fields is greater than
            // 100,000.Note that is it necessary to use a lambda expression rather than to explicitly define a delegate 
            // of type Predicate<T> as the second example illustrate.


            // Create an array of Point structures
            Point[] points =
                {
                new Point(100,200),
                new Point(150,250),
                new Point(250,375),
                new Point(275,390),
                new Point(296,400)

            };

            // Define the Predicate<T> delegate.
            Predicate<Point> predicate = FindPoints;

            // Find the first Point structure for whitch x times y is greater than 100000
            Point first = Array.Find(points, predicate);

            // Display the first structure found.
            Console.WriteLine($"Found：X={first.X},Y={first.Y}");

            Console.ReadKey();
        }

        private static bool FindPoints(Point ptn)
        {
            return ptn.X * ptn.Y > 100000;
        }
    }
}

The following example is identical to the previous example, except that it uses a lambda expression to represent the Predicate delegate

   // Create an array of Point structures
            Point[] points =
                {
                new Point(100,200),
                new Point(150,250),
                new Point(250,375),
                new Point(275,390),
                new Point(296,400)

            };

            // Define the Predicate<T> delegate.
            Predicate<Point> predicate = FindPoints;

            // Find the first Point structure for whitch x times y is greater than 100000
            Point first = Array.Find(points, x => x.X * x.Y > 100000 );

            // Display the first structure found.
            Console.WriteLine($"Found：X={first.X},Y={first.Y}");

            Console.ReadKey();
        }

Array.FindAll的用法

using System;
using System.Reflection;
using System.Collections.Generic;
namespace Predicate_過濾
{
 
    class Program
    {
        static void Main(string[] args)
        {

            List<Student> studens = new List<Student>
            {
                new Student("asd",18,100),
                new Student("qwe",20,60),
                new Student("dfg",30,70),
                new Student("vbn",56,89)
            };

           foreach(var stu in studens.FindAll(x=>x.Age>20).FindAll(y=>y.Score>80))
            {
                Console.WriteLine($"Name:{stu.Name} \t Age:{stu.Age} \t Score:{stu.Score}");
            }
            Console.ReadKey();
        }

        
    }
    class Student
    {
        public Student(string name,int age,int score)
        {
            this.Name = name;
            this.Age = age;
            this.Score = score;
        }
        public int Score { get; set; }
        public int Age { get; set; }
        public string Name { get; set; }
    }
}

參考