From传值

string value = string.Empty;
            using (Form2 frm = new Form2())
            {
                if (frm.ShowDialog() == DialogResult.OK)
                {
                    //value就是Form2关闭的时候传出的
                    value = frm.OutValue;
                }
            }
            MessageBox.Show(value);

public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }
 
        private void Form2_Load(object sender, EventArgs e)
        {
 
        }
 
        public string OutValue;
 
        protected override void OnClosing(CancelEventArgs e)
        {
            base.OnClosing(e);
 
            this.OutValue = "value";
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            this.DialogResult=DialogResult.OK;
            this.Close();
        }
    }