新增的Application.OpenForms属性

窗体布局：

然后代码：

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

namespace FormCollection
{
    public partial class frmMain : Form
    {
        private int nNumber = 1;

        public frmMain()
        {
            InitializeComponent();
        }

        private void frmMain_Load(object sender, EventArgs e)
        {
            RefreshListBox();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Form form = new Form();
            form.Name = nNumber.ToString();
            form.Text = nNumber.ToString();
            form.Show();
            nNumber++;
            RefreshListBox();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (-1 == listBox1.SelectedIndex)
            {
                return;
            }
            Application.OpenForms[listBox1.Items[listBox1.SelectedIndex].ToString()].Close();
            RefreshListBox();
        }

        private void RefreshListBox()
        {
            listBox1.Items.Clear();
            foreach (Form form in Application.OpenForms)
            {
                listBox1.Items.Add(form.Name);
            }
        }
    }
}