设计模式のFilterPattern（过滤器模式）----结构模式

一、产生背景

　　我们有一堆“人”的对象，我们应该怎么选择出其中的男性、女性或者其他类型的呢？这时候我们可以用过滤器模式

二、通常做法

　　我们将创建一个 Person 对象、Criteria 接口和实现了该接口的实体类，来过滤 Person 对象的列表。CriteriaPattern，我们的演示类使用 Criteria 对象，基于各种标准和它们的结合来过滤 Person 对象的列表。

三、实例

1、创建person类

namespace FilterPattern
{
    public class Person
    {

        private string name;
        private string gender;
        private string maritalStatus;

        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;
        }
    }
}

2、建立筛选标准

namespace FilterPattern
{
    public interface ICriteria
    {
         List<Person> MeetCriteria(List<Person> persons);
    }
}

    public class CriteriaMale : ICriteria
    {
        public List<Person> MeetCriteria(List<Person> persons)
        {
            List<Person> malePersons = new List<Person>();
            foreach (Person p in persons)
            {
                if (p.GetGender().Equals("Male"))
                malePersons.Add(p);
            }
            return malePersons;
        }
    }

    public class CriteriaFeMale : ICriteria
    {
        public List<Person> MeetCriteria(List<Person> persons)
        {
            List<Person> femalePersons = new List<Person>();
            foreach (Person p in persons)
            {
                if (p.GetGender().Equals("Female"))
                    femalePersons.Add(p);
            }
            return femalePersons;
        }
    }

    public class CriteriaSingle : ICriteria
    {
        public List<Person> MeetCriteria(List<Person> persons)
        {
            List<Person> singlePersons = new List<Person>();
            foreach (Person p in persons)
            {
                if (p.GetGender().Equals("Single"))
                    singlePersons.Add(p);
            }
            return singlePersons;
        }
    }

    public class AndCriteria : ICriteria
    {
        private ICriteria criteria;
        private ICriteria otherCriteria;
        public AndCriteria(ICriteria criteria, ICriteria otherCriteria)
        {
            this.criteria = criteria;
            this.otherCriteria = otherCriteria;
        }
        
        public List<Person> MeetCriteria(List<Person> persons)
        {
            List<Person> firstCriteriaPersons = criteria.MeetCriteria(persons);
            return otherCriteria.MeetCriteria(firstCriteriaPersons);
        }
    }

    public class OrCriteria : ICriteria
    {
        private ICriteria criteria;
        private ICriteria otherCriteria;
        public OrCriteria(ICriteria criteria, ICriteria otherCriteria)
        {
            this.criteria = criteria;
            this.otherCriteria = otherCriteria;
        }

        public List<Person> MeetCriteria(List<Person> persons)
        {
            List<Person> firstCriteriaItems = criteria.MeetCriteria(persons);
            List<Person> otherCriteriaItems = otherCriteria.MeetCriteria(persons);

            foreach (Person person in otherCriteriaItems)
            {
                if (!firstCriteriaItems.Contains(person))
                {
                    firstCriteriaItems.Add(person);
                }
            }
            return firstCriteriaItems;
        }
    }

3、客户端调用

    class Program
    {
        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"));

            ICriteria male = new CriteriaMale();
            ICriteria female = new CriteriaFeMale();
            ICriteria single = new CriteriaSingle();
            ICriteria singleMale = new AndCriteria(single, male);
            ICriteria 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.ReadLine();
        }

        public static void PrintPersons(List<Person> persons)
        {
            foreach (Person person in persons)
            {
                Console.WriteLine("Person : [ Name : " + person.GetName()
                   + ", Gender : " + person.GetGender()
                   + ", Marital Status : " + person.GetMaritalStatus()
                   + " ]");
            }
        }
    }

四、设计模式分析

优点：结构清晰，解耦合

缺点：使类型编的复杂

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