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前言
本文主要講解如何利用C#語(yǔ)言自身的特性來對(duì)一個(gè)類的功能進(jìn)行豐富與增強(qiáng)，便于拓展現(xiàn)有項(xiàng)目的一些功能。
拓展方法
擴(kuò)展方法被定義為靜態(tài)方法，通過實(shí)例方法語(yǔ)法進(jìn)行調(diào)用。方法的第一個(gè)參數(shù)指定該方法作用于哪個(gè)類型，并且該參數(shù)以 this 修飾符為前綴。僅當(dāng)使用 using 指令將命名空間顯式導(dǎo)入到源代碼中之后，擴(kuò)展方法才可使用。
namespace Extensions
{
public static class StringExtension
{
public static DateTime ToDateTime(this string source)
{
DateTime.TryParse(source, out DateTime result);
return result;
}
}
}
注意：
繼承
繼承 面向?qū)ο蟮囊粋€(gè)特性，屬于Is a 關(guān)系，比如說Student繼承Person,則說明Student is a Person。子類可以通過重寫父類的方法或添加新的方法來實(shí)現(xiàn)對(duì)父類的拓展。
namespace Inherit
{
public class Persion
{
public string Name { get; set; }
public int Age { get; set; }
public void Eat()
{
Console.WriteLine("吃飯");
}
public void Sleep()
{
Console.WriteLine("睡覺");
}
}
public class Student : Persion
{
public void Study()
{
Console.WriteLine("學(xué)習(xí)");
}
public new void Sleep()
{
Console.WriteLine("做作業(yè)，復(fù)習(xí)功課");
base.Sleep();
}
}
}
繼承的缺點(diǎn)：
組合
組合就是在設(shè)計(jì)類的時(shí)候把需要用到的類作為成員變量加入到當(dāng)前類中。
組合的優(yōu)缺點(diǎn)：
優(yōu)點(diǎn)：
缺點(diǎn)：
建議多使用組合，少用繼承
裝飾者模式
裝飾者模式指在不改變?cè)惗x及繼承關(guān)系的情況跟下，動(dòng)態(tài)的拓展一個(gè)類的功能，就是利用創(chuàng)建一個(gè)包裝類（wrapper）來裝飾（decorator）一個(gè)已有的類。
包含角色：
被裝飾者：
裝飾者：
在裝飾者模式中必然會(huì)有一個(gè)最基本，最核心，最原始的接口或抽象類充當(dāng)component和decorator的抽象組件
實(shí)現(xiàn)要點(diǎn)：
namespace Decorator
{
/// <summary>
/// Component 抽象者裝飾者
/// </summary>
public interface IStudent
{
void Learn();
}
/// <summary>
/// ConcreteComponent 具體被裝飾者
/// </summary>
public class Student : IStudent
{
private string _name;
public Student(string name)
{
this._name = name;
}
public void Learn()
{
System.Console.WriteLine(this._name + "學(xué)習(xí)了以上內(nèi)容");
}
}
/// <summary>
/// Decorator 裝飾者
/// </summary>
public abstract class Teacher : IStudent
{
private IStudent _student;
public Teacher(IStudent student)
{
this._student = student;
}
public virtual void Learn()
{
this.Rest();
this._student.Learn();
}
public virtual void Rest()
{
Console.WriteLine("課間休息");
}
}
/// <summary>
/// ConcreteDecorator 具體裝飾者
/// </summary>
public class MathTeacher : Teacher
{
private String _course;
public MathTeacher(IStudent student, string course) : base(student)
{
this._course = course;
}
public override void Learn()
{
System.Console.WriteLine("學(xué)習(xí)新內(nèi)容：" + this._course);
base.Learn();
}
public override void Rest()
{
System.Console.WriteLine("課間不休息，開始考試");
}
}
/// <summary>
/// ConcreteDecorator 具體裝飾者
/// </summary>
public class EnlishTeacher : Teacher
{
private String _course;
public EnlishTeacher(IStudent student, string course) : base(student)
{
this._course = course;
}
public override void Learn()
{
this.Review();
System.Console.WriteLine("學(xué)習(xí)新內(nèi)容：" + this._course);
base.Learn();
}
public void Review()
{
System.Console.WriteLine("復(fù)習(xí)英文單詞");
}
}
public class Program
{
static void Main(string[] args)
{
IStudent student = new Student("student");
student = new MathTeacher(student, "高數(shù)");
student = new EnlishTeacher(student, "英語(yǔ)");
student.Learn();
}
}
}
裝飾者模式優(yōu)缺點(diǎn)：
優(yōu)點(diǎn)：
缺點(diǎn)：
代理模式
代理模式就是給一個(gè)對(duì)象提供一個(gè)代理對(duì)象，并且由代理控制原對(duì)象的引用。
包含角色：
靜態(tài)代理
動(dòng)態(tài)代理涉及到反射技術(shù)相對(duì)靜態(tài)代理會(huì)復(fù)雜很多，掌握好動(dòng)態(tài)代理對(duì)AOP技術(shù)有很大幫助
namespace Proxy
{
/// <summary>
/// 共同抽象角色
/// </summary>
public interface IBuyHouse
{
void Buy();
}
/// <summary>
/// 真實(shí)買房人，被代理角色
/// </summary>
public class Customer : IBuyHouse
{
public void Buy()
{
System.Console.WriteLine("買房子");
}
}
/// <summary>
/// 中介-代理角色
/// </summary>
public class CustomerProxy : IBuyHouse
{
private IBuyHouse target;
public CustomerProxy(IBuyHouse buyHouse)
{
this.target = buyHouse;
}
public void Buy()
{
System.Console.WriteLine("篩選符合條件的房源");
this.target.Buy();
}
}
public class Program
{
static void Main(string[] args)
{
IBuyHouse buyHouse = new CustomerProxy(new Customer());
buyHouse.Buy();
System.Console.ReadKey();
}
}
}
動(dòng)態(tài)代理
namespace DynamicProxy
{
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
/// <summary>
/// 方法攔截器接口
/// </summary>
public interface IMethodInterceptor
{
/// <summary>
/// 調(diào)用攔截器
/// </summary>
/// <param name="targetMethod">攔截的目標(biāo)方法</param>
/// <param name="args">攔截的目標(biāo)方法參數(shù)列表</param>
/// <returns>攔截的目標(biāo)方法返回值</returns>
object Interceptor(MethodInfo targetMethod, object[] args);
}
/// <summary>
/// 代理類生成器
/// </summary>
public class ProxyFactory : DispatchProxy
{
private IMethodInterceptor _interceptor;
/// <summary>
/// 創(chuàng)建代理類實(shí)例
/// </summary>
/// <param name="targetType">要代理的接口</param>
/// <param name="interceptor">攔截器</param>
/// <returns></returns>
public static object CreateInstance(Type targetType, IMethodInterceptor interceptor)
{
object proxy = GetProxy(targetType);
((ProxyFactory)proxy).GetInterceptor(interceptor);
return proxy;
}
/// <summary>
/// 創(chuàng)建代理類實(shí)例
/// </summary>
/// <param name="targetType">要代理的接口</param>
/// <param name="interceptorType">攔截器</param>
/// <param name="parameters">攔截器構(gòu)造函數(shù)參數(shù)值</param>
/// <returns>代理實(shí)例</returns>
public static object CreateInstance(Type targetType, Type interceptorType, params object[] parameters)
{
object proxy = GetProxy(targetType);
((ProxyFactory)proxy).GetInterceptor(interceptorType, parameters);
return proxy;
}
/// <summary>
/// 創(chuàng)建代理類實(shí)例
/// </summary>
/// <typeparam name="TTarget">要代理的接口</typeparam>
/// <typeparam name="TInterceptor">攔截器</typeparam>
/// <param name="parameters">攔截器構(gòu)造函數(shù)參數(shù)值</param>
/// <returns></returns>
public static TTarget CreateInstance<TTarget, TInterceptor>(params object[] parameters) where TInterceptor : IMethodInterceptor
{
object proxy = GetProxy(typeof(TTarget));
((ProxyFactory)proxy).GetInterceptor(typeof(TInterceptor), parameters);
return (TTarget)proxy;
}
/// <summary>
/// 獲取代理類
/// </summary>
/// <param name="targetType"></param>
/// <returns></returns>
private static object GetProxy(Type targetType)
{
MethodCallExpression callexp = Expression.Call(typeof(DispatchProxy), nameof(DispatchProxy.Create), new[] { targetType, typeof(ProxyFactory) });
return Expression.Lambda<Func<object>>(callexp).Compile()();
}
/// <summary>
/// 獲取攔截器
/// </summary>
/// <param name="interceptorType"></param>
/// <param name="parameters"></param>
private void GetInterceptor(Type interceptorType, object[] parameters)
{
Type[] ctorParams = parameters.Select(x => x.GetType()).ToArray();
IEnumerable<ConstantExpression> paramsExp = parameters.Select(x => Expression.Constant(x));
NewExpression newExp = Expression.New(interceptorType.GetConstructor(ctorParams), paramsExp);
this._interceptor = Expression.Lambda<Func<IMethodInterceptor>>(newExp).Compile()();
}
/// <summary>
/// 獲取攔截器
/// </summary>
/// <param name="interceptor"></param>
private void GetInterceptor(IMethodInterceptor interceptor)
{
this._interceptor = interceptor;
}
/// <summary>
/// 執(zhí)行代理方法
/// </summary>
/// <param name="targetMethod"></param>
/// <param name="args"></param>
/// <returns></returns>
protected override object Invoke(MethodInfo targetMethod, object[] args)
{
return this._interceptor.Interceptor(targetMethod, args);
}
}
/// <summary>
/// 表演者
/// </summary>
public interface IPerform
{
/// <summary>
/// 唱歌
/// </summary>
void Sing();
/// <summary>
/// 跳舞
/// </summary>
void Dance();
}
/// <summary>
/// 具體的表演者——?jiǎng)⒌氯A Andy
/// </summary>
public class AndyPerformer : IPerform
{
public void Dance()
{
System.Console.WriteLine("給大家表演一個(gè)舞蹈");
}
public void Sing()
{
System.Console.WriteLine("給大家唱首歌");
}
}
/// <summary>
/// 經(jīng)紀(jì)人——負(fù)責(zé)演員的所有活動(dòng)
/// </summary>
public class PerformAgent : IMethodInterceptor
{
public IPerform _perform;
public PerformAgent(IPerform perform)
{
this._perform = perform;
}
public object Interceptor(MethodInfo targetMethod, object[] args)
{
System.Console.WriteLine("各位大佬，要我們家藝人演出清閑聯(lián)系我");
object result = targetMethod.Invoke(this._perform, args);
System.Console.WriteLine("各位大佬，表演結(jié)束該付錢了");
return result;
}
}
public class Program
{
static void Main(string[] args)
{
IPerform perform;
//perform = ProxyFactory.CreateInstance<IPerform, PerformAgent>(new AndyPerformer());
//perform.Sing();
//perform.Dance();
ServiceCollection serviceDescriptors = new ServiceCollection();
serviceDescriptors.AddSingleton<IPerform>(ProxyFactory.CreateInstance<IPerform, PerformAgent>(new AndyPerformer()));
IServiceProvider serviceProvider = serviceDescriptors.BuildServiceProvider();
perform = serviceProvider.GetService<IPerform>();
perform.Sing();
perform.Dance();
System.Console.ReadKey();
}
}
}
總結(jié)
參考引用
利用.NET Core類庫(kù)System.Reflection.DispatchProxy實(shí)現(xiàn)簡(jiǎn)易Aop
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