using System;
using System.Windows.Forms;

public class MyForm : Form
{
    private ListBox listBox;
    private ContextMenuStrip contextMenuStrip;

    public MyForm()
    {
        listBox = new ListBox();
        contextMenuStrip = new ContextMenuStrip();

        // 添加菜單項目
        ToolStripMenuItem addItem = new ToolStripMenuItem("Add");
        ToolStripMenuItem deleteItem = new ToolStripMenuItem("Delete");

        // 將菜單項目添加到 ContextMenuStrip
        contextMenuStrip.Items.Add(addItem);
        contextMenuStrip.Items.Add(deleteItem);

        // 將 ContextMenuStrip 關聯到 ListBox
        listBox.ContextMenuStrip = contextMenuStrip;

        // 設置事件處理
        listBox.MouseDown += ListBox_MouseDown;
        
        // 添加 ListBox 到窗體
        listBox.Dock = DockStyle.Fill;
        this.Controls.Add(listBox);
        
        // 添加一些示例項目
        listBox.Items.Add("Item 1");
        listBox.Items.Add("Item 2");
        listBox.Items.Add("Item 3");
    }

    private void ListBox_MouseDown(object sender, MouseEventArgs e)
    {
        if (e.Button == MouseButtons.Right)
        {
            // 獲取選中的項目
            int index = listBox.IndexFromPoint(e.Location);
            if (index != -1) // 有選中項目
            {
                contextMenuStrip.Items[1].Visible = true; // 顯示 Delete
            }
            else // 沒有選中項目
            {
                contextMenuStrip.Items[1].Visible = false; // 隱藏 Delete
            }
        }
    }

    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.Run(new MyForm());
    }
}