为什么CreateInstance会返回NULL?

onunix 2011-08-04 10:18:40

文件A：

using System;

using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;

using System.Threading;

using System.Windows.Forms;

namespace BackService
{

public class Program
{

}

public class MathClass//要定义为public
{

//私有变量
public static int m_testi;

private int x;

private int y;

//无参数的构造函数

public MathClass()
{

this.x = 0;

this.y = 0;

m_testi = 0;

}

public int Add()
{

return m_testi;

}

}

}

文件B：

using System;

using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using abcTest.view;

using System.Reflection;
using BackService;
using System.Windows.Forms;

namespace abcTest
{
public partial class LoginView : Form
{
public LoginView()
{
InitializeComponent();
this.ControlBox = false;
}

private void button1_Click(object sender, EventArgs e)
{

Assembly asm = Assembly.Load("BackService");

object obj = asm.CreateInstance("BackService.MathClass");

if (null == obj)
{

MessageBox.Show("动态创建对象失败！");

}
else
{
MessageBox.Show("创建好了！");
}

Type t = typeof(MathClass);

MessageBox.Show("开始调用方法！");

int result = (int)t.InvokeMember("Add", BindingFlags.InvokeMethod, null, obj, null);

string aa;

//aa.ToString(result);
string strresult = result.ToString();

MessageBox.Show(strresult);

}

private void button2_Click(object sender, EventArgs e)
{
Application.Exit();
}

//end class
}

}

这个为什么会出异常呢？
object obj = asm.CreateInstance("BackService.MathClass");

如果改成 object obj = asm.CreateInstance("MathClass");
则返回的obj为NULL。

应该如何修改呢？

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