C#winFrom中怎么把一个窗体文本框赋值给多个不同窗体，怎么判断窗体？

如果问题得到解决，请点我回答左上角的采纳和向上的箭头，谢谢

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 Q714723
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            new Form2().Show();
            new Form3().Show();
            new Form4().Show();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            foreach (Form item in Application.OpenForms)
            {
                if (item != this)
                    (item.Controls["textBox1"] as TextBox).Text = textBox1.Text;
            }
        }
    }
}