还有个小问题

C# code

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;using Microsoft.Office.Interop.Excel;namespace shangweiji{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        private void Form1_Load(object sender, EventArgs e)        {1：        Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.Application();2:         Workbook wbook = app.Workbooks.Open("D:\\sun", Type.Missing);3:         Worksheet worksheet = (Worksheet)wbook.Worksheets[1];            worksheet.Cells[2,1] = "jiweiqiang";            app.Visible = true;            string temp = ((Range)worksheet.Cells[1, 2]).Text;        }        private void button1_Click(object sender, EventArgs e)        {            Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.Application();            Workbook wbook = app.Workbooks.Open("D:\\sun", Type.Missing);            Worksheet worksheet = (Worksheet)wbook.Worksheets[1];            worksheet.Cells[9, 2] = "-20";         }    }}

请问下1,2,3处的代码该放在什么地方，才能使定义的worksheet在每个事件应用程序下都能使用。现在我放在form_load下的话button_click是用不到的。
本来想放到form1（）构造函数下的，可报错说不能引用非静态字段，属性和方法。
谢谢了

[解决办法]

C# code

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;using Microsoft.Office.Interop.Excel;namespace shangweiji{    public partial class Form1 : Form    {1：        Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.Application();2:         Workbook wbook = app.Workbooks.Open("D:\\sun", Type.Missing);3:         Worksheet worksheet = (Worksheet)wbook.Worksheets[1];        public Form1()        {            InitializeComponent();        }        private void Form1_Load(object sender, EventArgs e)        {            worksheet.Cells[2,1] = "jiweiqiang";            app.Visible = true;            string temp = ((Range)worksheet.Cells[1, 2]).Text;        }        private void button1_Click(object sender, EventArgs e)        {                        worksheet.Cells[9, 2] = "-20";         }    }}