弹出唯一窗口

主窗口后台代码：

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;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        //建立集合来记录
        List<Form> AllForm = new List<Form>();

        private void button1_Click(object sender, EventArgs e)
        {
            Form2 f2 = new Form2(this, textBox1.Text);//实例化类
            f2.Name = "f2";//重新给其name赋值，以免发生冲突
            OnlyOne(f2);
        }
        
        //保证弹出窗口唯一的方法，私有
        private void OnlyOne(Form FF)
        {
            bool hasForm = false;

            foreach (Form f in AllForm)
            {
                if (f.Name == FF.Name)
                {
                    hasForm = true;
                    f.WindowState = FormWindowState.Normal;
                    f.Focus();
                }
            }

            if (hasForm)
            {
                FF.Close();
            }
            else
            {
                AllForm.Add(FF);
                FF.Show();
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Form3 f3 = new Form3();
            f3.Name = "f3";
            OnlyOne(f3);
        }

        //弹出窗口关闭后，在集合里将其移除，避免误关或关闭后无法再次弹出
        public void RemoveForm(Form ff)
        {
            AllForm.Remove(ff);
        }

    }
}

弹出窗口的后台代码：

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;

namespace WindowsFormsApplication2
{
    public partial class Form2 : Form
    {
        Form1 F1 = null;
        public Form2(Form1 f1, string uname)
        {
            InitializeComponent();
            F1 = f1;

            label1.Text = uname + "，欢迎回来！";
        }

        private void Form2_FormClosing(object sender, FormClosingEventArgs e)
        {
            F1.RemoveForm(this);
        }
    }
}