注意将form2中的botton2的modyfier属性修改为public。

　　form1代码：

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

namespace test
{
public partial class Form1 : Form
{
Form2 frm = new Form2();
public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
this.Hide();
frm.Show();
frm.button2.Click +=button2_Click;
}
private void button2_Click(object sender, EventArgs e)
{
MessageBox.Show("form1");
this.Show();
}

private void Form1_Load(object sender, EventArgs e)
{

}
}
}

　　form2代码：

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

namespace test
{
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}

private void button2_Click(object sender, EventArgs e)
{
MessageBox.Show("form2");
this.Hide();
}
}
}