.net反射机实例说明（转）

.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();

    }

}

= = = = = == = == = == = == = == = == = == = == = == = == = == = == = == = == = == = =

(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";

        }

    }

}

= = = = = == = == = == = == = == = == = == = == = == = == = == = == = == = == = == = =

(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();

        }

    }

}

= = = = = == = == = == = == = == = == = == = == = == = == = == = == = == = == = == = =

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