Predicate C#

What is a Predicate?

The predicate is just a generic delegate that is defined in the .net framework class library. In the framework library, it is defined as

public delegate bool Predicate<T>(T obj);

This delegate is used for searching purposes.

Predicate Example

The FindAll() method in List<T> expects an instance of the predicate as a parameter. In the example below I show you how to do that.

  

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Linq.Expressions;

namespace PlayLambda

{

    public class Person

    {

        public string name;

        public int Age;

    }

    class Program

    {

        static void Main(string[] args)

        {

            Person P1 = new Person();

            P1.name = "Mike";

            P1.Age = 37;

            Person P2 = new Person();

            P2.name = "Tommy";

            P2.Age = 13;

            Person P3 = new Person();

            P3.name = "Kim";

            P3.Age = 27;

            List<Person> People = new List<Person>();

            People.Add(P1);

            People.Add(P2);

            People.Add(P3);

            Predicate<Person> myPredicate = IsDrinkingAge;

                     //FindAll() expects an instance of the Predicate as a parameter

            foreach (Person p in People.FindAll(myPredicate))

            {

                Console.WriteLine("This person can legally drink: " + p.name);

            }

        }

        static bool IsDrinkingAge(Person p)

        {

            //The signature of this method should match the signature of the predicate

            if (p.Age > 21)

            {

                return true;

            }

            else

            {

                return false;

            }

        }

    }

}

  

Shown below is the output of this program