.NET反射机制简介

      .NET反射机制为创建对象和调用其他方法提供了替代方案。比如为了提高代码的灵活性。但是问题确是我们要编写更多的代码来实现。
使用反射机制是有一些缺点的。其最大的缺点就是编译器无法对对象进行类型检查，此时IDE的智能感知将无能为力。但是他的真正优势又在什么地方呢？它提供了一种手段，将指定具体类推迟到了运行时刻。
使用反射机制调用方法的四步曲：
1 加载程序集
2 获取类的类型
3 创建该类的实例
4 调用该实例的方法

System.Reflection.Assembly类中有两个静态方法Assembly.Load(string assemblyName)和Assembly.LoadFrom(string fileName)来把程序集加载到应用程序序域中。
PS：在。NET中当一个对象被创建时，幕后到底发生了什么？当我们运行某一个应用程序时，.NET CLR会首先创建一个应用程序域来容纳这个应用程序，接着将应该引用的程序集加载到应用程序域中。其中MSCorLib.dll是一个程序集，它包含了很多系统命名空间及其子命名空间中的类：System;System.Text,System.IO等。该程序集合中。然后CLR加载正在运行的应用程序所属的程序集。
DEMO：

(1)namespace ClassLibrarySport
{
    public abstract class Sport
    {
        protected string name;
        public abstract string GetName();
        public abstract string GetDuration();
    }
}
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(2)namespace ClassLibrarySomeSports//该项目添加了对(1)的引用
{
    public class Football : ClassLibrarySport.Sport
    {
        public Football()
        {
            name = "Football";
        }
        public override string GetName()
        {
            return name;
        }
        public override string GetDuration()
        {
            return "four 15 minute quarters";
        }
    }
}
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(3)namespace ConsoleAssemblyTest//该项目添加了对(1)的引用
{
    class Program
    {
        static void Main(string[] args)
        {
            Assembly assembly =Assembly.LoadFrom(@"E:/ClassLibrarySomeSports/bin/Debug/ClassLibrarySomeSports.dll");
            Type[] types = assembly.GetTypes();

            Console.WriteLine("Get Type From ClassLibrarySomeSports.dll:");
            for (int i = 0; i < types.Length; i++)
            {
                Console.WriteLine(types[i].Name);
            }

            //使用GetConstructor()方法获取对应类型的构造器，从而构造出该类型的对象
            Console.WriteLine("Use Method GetConstructor():");
            ConstructorInfo ci = types[0].GetConstructor(new Type[0]);
            ClassLibrarySport.Sport sport = (ClassLibrarySport.Sport)ci.Invoke(new object[0]);
            Console.WriteLine(sport.GetName() + " has " + sport.GetDuration());

            //使用Activator.CreateInstance()方法构造出该类型的对象
            //使用assembly.CreateInstance()返回为null，？
            Console.WriteLine("Use Method CreateInstance():");
            ClassLibrarySport.Sport sport1 = (ClassLibrarySport.Sport)
Activator.CreateInstance(types[0]);
            Console.WriteLine(sport1.GetName() + " has " + sport1.GetDuration());

            //反射指定类型中的名称为“GetDuration”的方法，通过Invoke()方法执行该方法
            object objSport = Activator.CreateInstance(types[0]);
            MethodInfo method = types[0].GetMethod("GetDuration");
            object o = method.Invoke(objSport, new object[0]);
            Console.WriteLine(o as string);

            Console.Read();
        }
    }
}

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Output:
Get Type From ClassLibrarySomeSports.dll:
Football
Use Method GetConstructor():
Football has four 15 minute quarters
Use Method CreateInstance():
Football has four 15 minute quarters
four 15 minute quarters