using System;
using System.Collections;
using System.Drawing;
using System.Windows.Forms;

public class EnvironmentVars:Form
{
    Label label;

    public static void Main()
    {
        Application.Run(new EnvironmentVars());
    }
    public EnvironmentVars()
    {
        //设置窗体属性，这些属性属于基类Form
        Text = "Environment Variables";
        
        //动态创建Label控件
        label = new Label();
        label.Parent = this;
        label.Anchor = AnchorStyles.Left | AnchorStyles.Right;
        label.Location = new Point(Font.Height,Font.Height);
        label.Size = new Size(ClientSize.Width - 2 * Font.Height,Font.Height);
 
        //动态创建ListBox控件
        ListBox listbox = new ListBox();
        listbox.Parent = this;
        listbox.Location = new Point(Font.Height,3 * Font.Height);
        listbox.Size = new Size(12 * Font.Height,8 * Font.Height);
        listbox.Sorted = true;
        listbox.SelectedIndexChanged += new EventHandler(ListBoxOnSelectedIndexChanged);

        //获取环境变量
        IDictionary dict = Environment.GetEnvironmentVariables();
        string[] astr = new string[dict.Keys.Count];

        //将环境变量的键值（Key）显示到ListBox中
        dict.Keys.CopyTo(astr,0);
        listbox.Items.AddRange(astr);
        listbox.SelectedIndex = 0;

    }

    void ListBoxOnSelectedIndexChanged(object obj,EventArgs ea)
    {
        //获取用户点击的ListBox条目及数据
        ListBox listbox = (ListBox)obj;
        string strItem = (string)listbox.SelectedItem;

        //将对应键值的环境变量值显示到Label上
        label.Text = Environment.GetEnvironmentVariable(strItem);
    }
}