关于assembly.createinstance()返回对象不能成功完成类型转换的问题，请高手出招

Question

发现同样条件下activiator.createinstance工作而assembly.createinstance()不工作，不知道什么原因。请高手解释。
另：Assembly load的Exe文件是后附被测代码生成的，不存在类定义不一致的问题。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.Runtime.Remoting;
using testpurpose;

namespace _99testexe
{
    class Programa
    {
        static void Main(string[] args)
        {
            Assembly oa = Assembly.LoadFrom(@"D:\Projects\CsharpCore\testpurpose\bin\Debug\testpurpose.exe");

            Type ot = oa.GetTypes()[0];
            object obj1 = oa.CreateInstance(ot.FullName);

            foreach (MethodInfo om in ot.GetMethods())

                if (om.Name == "sayhi")
                    om.Invoke(obj1, null);//工作得很正常

            ObjectHandle oh = Activator.CreateInstance(oa.FullName, ot.FullName);
            testpurpose.Program obj2 = oh.Unwrap() as testpurpose.Program;
            obj2.sayhi();//工作得很正常

            object obj3 = oa.CreateInstance(ot.FullName);
            testpurpose.Program obj4 = obj3 as testpurpose.Program;//没有工作好。obj4为空。obj3是testpurpose.Program对象
            obj4.sayhi();//抛出nullexecption
            System.Console.ReadKey();

        }

    }
}

 

被测程序集如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace testpurpose
{
    public class Program
    {         
    
        public void sayhi()
        {
            System.Console.WriteLine("say hi");
        }
       
        public static void sayhello()
        {
           
            System.Console.WriteLine("say hello from static");
        }
        static void Main(string[] args)
        {
           
            System.Console.WriteLine("say hello from main.");
        }
    }
}

---

Johnson Dai

Answer 1

已查：

            object obj3 = Activator.CreateInstance(ot);
            testpurpose.Program obj4 = obj3 as testpurpose.Program;//无法完成 转换
            obj4.sayhi();

   该语句同样出错。

怀疑：activator.createinstance()返回的objecthandler 经过unwrap()得到的object和activator.createinstance()直接返回的对象不一样！

问题是为啥呢？

---

Johnson Dai

Answer 2

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.Runtime.Remoting;
using testpurpose;

namespace _99testexe
{
    class Programa
    {
        static void Main(string[] args)
        {
            Assembly oa = Assembly.LoadFrom(@"D:\Projects\CsharpCore\testpurpose\bin\Debug\testpurpose.exe");

            Type ot = oa.GetTypes()[0];
            object obj1 = oa.CreateInstance(ot.FullName);

            foreach (MethodInfo om in ot.GetMethods())

                if (om.Name == "sayhi")
                    om.Invoke(obj1, null);

            ObjectHandle oh = Activator.CreateInstance(oa.FullName, ot.FullName);
            testpurpose.Program obj2 = oh.Unwrap() as testpurpose.Program;
            obj2.sayhi();
          
            object obj3=AppDomain.CurrentDomain.CreateInstanceAndUnwrap(oa.FullName, ot.FullName);
            testpurpose.Program obj4 = obj3 as testpurpose.Program;
            obj4.sayhi();

            object obj5 = AppDomain.CurrentDomain.CreateInstance(oa.FullName, ot.FullName);
            testpurpose.Program obj6 = oh.Unwrap() as testpurpose.Program;
            obj6.sayhi();

            object obj7 = oa.CreateInstance(ot.FullName);
           
            testpurpose.Program obj8 = obj7 as testpurpose.Program;
            obj8.sayhi();
           //except this not working, above all works well. So,what happened to activator.createinstance() returned object?? (assembly.createinstance is calling activator.createinstance. so ignore it.
            System.Console.ReadKey();

        }

    }
}

---

Johnson Dai

Answer 3

已查出原因。

在reference里面加载的exe和loadfrom加载的exe算两个不同的程序集。（尽管代码完全一致）。

要消除这个问题可以把loadfrom里面的路径去掉。

            Assembly oa = Assembly.Load("testpurpose");
这样找到的是同一个程序集。就可以随便转换了。

结贴。

---

Johnson Dai