后期绑定的几种方法

 

一、使用System.Activator类

System.Activator提供了两个静态方法:createinstance()和createinstancefrom()，如果包含类的程序集未出现在Appdomain中，调用:createinstance()和createinstancefrom()会导致该程序集被载入。

using System;

using System.Reflection;

 

namespace ConsoleApplication5

{

    classProgram

    {

        staticvoid Main(string[] args)

        {

            Assemblyassembly = Assembly.Load("Foo.dll");

            Typetype = assembly.GetType("NMFoo.Calc");

            objectobj = Activator.CreateInstance(type);

        }

    }

}

二、  使用System.Appdomain。与之前的Activator.CreateInstance类似，不过通过他们可以选择将对象创建在哪个Appdomain中，此外“AndUnwarp()”版本会返回一个对对象的直接引用。

using System;

using System.Reflection;

class Program {

   staticvoid Main() {

      objectobj = AppDomain.CurrentDomain.CreateInstanceAndUnwrap(

                                  "Foo.dll", "NMFoo.Calc");

 

   }

}

三、使用System.Reflecton.ConstructorInfo类，该类的invoke()方法在内部为构造函数创建了一个后期绑定，并通过这个绑定调用构造函数

using System;

using System.Reflection;

 

namespace ConsoleApplication5

{

    classProgram

    {

        staticvoid Main(string[] args)

        {

            Assemblyassembly = Assembly.LoadFrom(@"C:\Foo.dll");

            Typetype = assembly.GetType("NMFoo.Calc");

            ConstructorInfoconstructorInfo = type.GetConstructor(new Type[0]);

            objectobj = constructorInfo.Invoke(new object[0]);

        }

    }

}

 

四、  使用System.Type类

通过System.Type类的非静态方法Invokemember()可以创建一个在编译期间未知的类的实例，只需要在调用的时候使用BIndingFlages枚举量中的CreateInstance即可

using System;

using System.Reflection;

 

namespace ConsoleApplication5

{

    classProgram

    {

        staticvoid Main(string[] args)

        {

            Assemblyassembly = Assembly.LoadFrom(@"C:\Foo.dll");

            Typetype = assembly.GetType("NMFoo.Calc");

            Objectobj = type.InvokeMember(

              null, // Don't need toprovide a name for calling a constructor.

              BindingFlags.CreateInstance,

              null, // Don't need abinder.

              null, // Don't need atarget object since we build it.

              new Object[0]); // No parameters.

            //Here, 'obj' is a reference toward an instance of NMFoo.Calc.

        }

    }

}

五、对于数组和委托对象的实例

  为创建一个数组，必须调用System.Array类中的静态方法Createinstance()

 为创建一个委托对象，必须调用System.Delegate类中的CreateDelegate()方法

 

六、一次绑定，多次调用

 

using System;

using System.Reflection;

 

namespace ConsoleApplication5

{

    classProgram

    {

        staticvoid Main()

        {

            objectobj = AppDomain.CurrentDomain.CreateInstanceAndUnwrap(

                                       "Foo.dll", "NMFoo.Calc");

            Typetype = obj.GetType();

            //Create a late bind with the 'sum'?method.

            MethodInfomethodInfo = type.GetMethod("Sum");

            object[]parameters = new object[2];

            parameters[0] = 7;

            parameters[1] = 8;

            intresult;

            //10 calls to 'Sums'

            //for (int i = 0;i < 10; i++)

                result = (int)methodInfo.Invoke(obj, parameters);

                Console.WriteLine(Convert.ToString(result));

 

        }

    }

}

 

七、利用接口：使用后期绑定的正确方法

1、 创建包含接口的程序集的代码(InterfaceAsm.CS)

using System;

using System.Collections.Generic;

using System.Text;

 

namespace NMFoo

{

    publicinterface ICalc

    {

        intSum(int a, intb);

    }

}

2、 创建目标类的程序集的代码(ClassAsm.CS)

using System;

using System.Collections.Generic;

using System.Text;

 

namespace NMFoo

{

    publicclass CalcWithInterface:ICalc

    {

        publicCalcWithInterface()

        {

            Console.WriteLine("Calc.constructor called!");

        }

 

        publicint Sum(int a, int b)

        {

            Console.WriteLine("method Calc.Sum() Called!");

            returna + b;

 

        }

    }

 

}

3、 在编译期目标类未知的客户程序集的代码(ProgramAsm.CS)

using System;

using System.Reflection;

using NMFoo;

using System.IO;

 

namespace Main

{

    classProgram

    {

        staticvoid Main(string[] args)

        {

            //Console.WriteLine(System.Environment.CurrentDirectory);

            ICalcobj = AppDomain.CurrentDomain.CreateInstanceAndUnwrap("ClassAsm.dll", "NMFoo.CalcWithInterface")as ICalc;

            //intresult = obj.Sum(7, 8);

            Console.WriteLine(System.Environment.CurrentDirectory);

        }

    }

}

4、