关于C# 窗体之间传值

1、父窗体

/// <summary>
/// 弹窗
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void btnPopWin_Click(object sender, EventArgs e)
{
    FormItem formItem = new FormItem(this);
    formItem.itemno = "1";
    formItem.Show();
}

/// <summary>
/// 传值
/// </summary>
/// <param name="str"></param>
public void setValue(string str)
{
    txtSub.Text = str;
}

2、子窗体

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

namespace oms
{
    public partial class FormItem : Form
    {
        public string itemno = "";

        FrmMain frmMain = new FrmMain();
        public FormItem(FrmMain frm)
        {
            frmMain = frm;
            InitializeComponent();
        }

        /// <summary>
        /// 设置父窗体的值
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnSet_Click(object sender, EventArgs e)
        {
            // 方法1 FormMain.Designer.cs 控件的属性 private 调整为 public
            // public System.Windows.Forms.TextBox txtLine;
            string str = txtTemp.Text;
            frmMain.txtLine.Text = str;
            // 方法2 定义一个 public 函数
            frmMain.setValue(str);
        }

        /// <summary>
        /// 初始化传值
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void FormItem_Load(object sender, EventArgs e)
        {
            txtTemp.Text = itemno;
        }
    }
}