访问listbox对象并在类中将其全局用作字符串

我想将列表框中选定的项用作字符串。从列表Box1_SelectedIndexChanged中它运行良好。我如何在全球范围内使用它我的课？

我把它放在了班上的最前面，并试图让它保持静态，但我得到了以下错误。有人能告诉我如何引用它吗？

错误1非静态字段需要对象引用，方法或属性

public class
{
static string listme = listBox1.GetItemText(listBox1_SelectedIndexChanged);
 public Form1()
        {
            InitializeComponent();
            this.Shown += new EventHandler(listBox1_SelectedIndexChanged);
        }
public void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
             listBox1.SelectedIndex = 0;
           string items = listBox1.GetItemText(listBox1.SelectedItem);
           MessageBox.Show(Backups + @"'" + items);

        }

public class
{
static string listme;
public Form1()
        {
            InitializeComponent();
            this.Shown += new EventHandler(listBox1_SelectedIndexChanged);
        }
public void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            listBox1.SelectedIndex = 0;
            listme = listBox1.GetItemText(listBox1.SelectedItem);
            MessageBox.Show(Backups + @"'" + listme);

        }