設計模式【過濾器模式Filter Pattern】

過濾器模式

過濾器模式（Filter Pattern）或標準模式（Criteria Pattern）是一種設計模式，這種模式允許開發人員使用不同的標準來過濾一組對象，通過邏輯運算以解耦的方式把它們連接起來。這種類型的設計模式屬於結構型模式，它結合多個標準來獲得單一標準。

實現

我們將創建一個 Person 對象、Criteria 接口和實現了該接口的實體類，來過濾 Person 對象的列表。CriteriaPatternDemo，我們的演示類使用 Criteria 對象，基於各種標準和它們的結合來過濾 Person 對象的列表。

步驟 1

創建一個類，在該類上應用標準。

Person.cs

namespace Filter_Pattern
{
    class Person
    {
        string name;          //名字
        string gender;        //性別
        string maritalStatus; //婚姻狀況

        public Person(string name, string gender, string maritalStatus)
        {
            this.name = name;
            this.gender = gender;
            this.maritalStatus = maritalStatus;
        }

        public string getName()
        {
            return name;
        }

        public string getGender()
        {
            return gender;
        }

        public string getMaritalStatus()
        {
            return maritalStatus;
        }
    }
}

步驟 2

爲標準（Criteria）創建一個接口。

Criteria.cs

using System.Collections.Generic;
namespace Filter_Pattern
{
    interface Criteria
    {
        //過濾器的規則函數
        List<Person> meetCriteria(List<Person> persons);
    }
}

步驟 3

創建實現了 Criteria 接口的實體類。

CriteriaMale.cs

using System.Collections.Generic;
namespace Filter_Pattern
{
    class CriteriaMale : Criteria
    {
        public List<Person> meetCriteria(List<Person> persons)
        {
            //過濾出滿足性別爲‘MALE’的一些人
            List<Person> malePersons = new List<Person>();
            foreach (var person in persons)
            {
                if (person.getGender().Equals("Male"))
                    malePersons.Add(person);
            }
            return malePersons;
        }
    }
}

CriteriaFemale.cs

using System.Collections.Generic;
namespace Filter_Pattern
{
    class CriteriaFemale : Criteria
    {
        public List<Person> meetCriteria(List<Person> persons)
        {
            //過濾出滿足性別爲‘FEMALE’的一些人
            List<Person> femalPerson = new List<Person>();
            foreach (var person in persons)
            {
                if (person.getGender().Equals("Female"))
                    femalPerson.Add(person);
            }
            return femalPerson;
        }
    }
}

CriteriaSingle.cs

using System.Collections.Generic;
namespace Filter_Pattern
{
    class CriteriaSingle : Criteria
    {
        public List<Person> meetCriteria(List<Person> persons)
        {
            //過濾出單身人羣
            List<Person> singlePersons = new List<Person>();
            foreach (var person in persons)
            {
                if (person.getMaritalStatus().Equals("Single"))
                    singlePersons.Add(person);
            }
            return singlePersons;
        }
    }
}

AndCriteria.cs

using System.Collections.Generic;
namespace Filter_Pattern
{
    class AndCriteria : Criteria
    {
        Criteria criteria;
        Criteria otherCriteria;

        public AndCriteria(Criteria criteria, Criteria otherCriteria)
        {
            this.criteria = criteria;
            this.otherCriteria = otherCriteria;
        }
        //過濾出同時滿足criteria和otherCriteria規則的人
        public List<Person> meetCriteria(List<Person> persons)
        {
            List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);
            return otherCriteria.meetCriteria(firstCriteriaPersons);
        }
    }
}

OrCriteria.cs

using System.Collections.Generic;
namespace Filter_Pattern
{
    class OrCriteria : Criteria
    {
        Criteria criteria;
        Criteria otherCriteria;

        public OrCriteria(Criteria criteria, Criteria otherCriteria)
        {
            this.criteria = criteria;
            this.otherCriteria = otherCriteria;
        }
        //過濾出滿足criteria或者otherCriteria過濾規則的人
        public List<Person> meetCriteria(List<Person> persons)
        {
            List<Person> firstCriteriaItems = criteria.meetCriteria(persons);
            List<Person> otherCriteriaItems = otherCriteria.meetCriteria(persons);
            foreach (var person in otherCriteriaItems)
            {
                if (!firstCriteriaItems.Contains(person))
                    firstCriteriaItems.Add(person);
            }
            return firstCriteriaItems;
        }
    }
}

步驟4

使用不同的標準（Criteria）和它們的結合來過濾 Person 對象的列表。

CriteriaPatternDemo.cs

using System;
using System.Collections.Generic;
namespace Filter_Pattern
{
    class CriteriaPatternDemo
    {
        static void Main(string[] args)
        {
            List<Person> persons = new List<Person>();
            persons.Add(new Person("Robert","Male", "Single"));
            persons.Add(new Person("John","Male", "Married"));
            persons.Add(new Person("Laura","Female", "Married"));
            persons.Add(new Person("Diana","Female", "Single"));
            persons.Add(new Person("Mike","Male", "Single"));
            persons.Add(new Person("Bobby","Male", "Single"));

            Criteria male = new CriteriaMale();
            Criteria female = new CriteriaFemale();
            Criteria single = new CriteriaSingle();
            Criteria singleMale = new AndCriteria(single, male);
            Criteria singleOrFemale = new OrCriteria(single, female);

            Console.WriteLine("Males: ");
            printPersons(male.meetCriteria(persons));

            Console.WriteLine("\nFemales: ");
            printPersons(female.meetCriteria(persons));

            Console.WriteLine("\nSingle Males: ");
            printPersons(singleMale.meetCriteria(persons));

            Console.WriteLine("\nSingle Or Females: ");
            printPersons(singleOrFemale.meetCriteria(persons));

            Console.Read();
        }

     
        public static void printPersons(List<Person> persons)
        {
            foreach (var person in persons)
	        {
		         Console.WriteLine("Person : [ Name : " + person.getName() 
                +", Gender : " + person.getGender() 
                +", Marital Status : " + person.getMaritalStatus()
                +" ]");
	        }
        } 
    }
}

步驟 5

驗證輸出。

Males: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : John, Gender : Male, Marital Status : Married ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]

Females: 
Person : [ Name : Laura, Gender : Female, Marital Status : Married ]
Person : [ Name : Diana, Gender : Female, Marital Status : Single ]

Single Males: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]

Single Or Females: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : Diana, Gender : Female, Marital Status : Single ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]
Person : [ Name : Laura, Gender : Female, Marital Status : Married ]