Use delegates to pass values between forms

The traditional way

Create a public data resource class to store the value of Form 2's TextBox:

    public class ComValue
    {
       public static string Txtvalue { get; set; }
    }

Code for Form 1:

        private void button1_Click(object sender, EventArgs e)
        {
            Form2 f2 = new Form2();
            f2.Show();
        } 
　　　　　//Use timer to keep copying label2
        private void timer1_Tick(object sender, EventArgs e)
        {
            label2.Text = ComValue.Txtvalue;
        }

Code for Form 2:

        private void button1_Click(object sender, EventArgs e)
        {
            Form2 f2 = new Form2();
            f2.Show();
        }
        private void timer1_Tick(object sender, EventArgs e)
        {
            label2.Text = ComValue.Txtvalue;
        }

This way consumes resources by using the timer.

Second, use the delegate to pass the value, and pass the method of assigning form1 to lable2 to form2

Code for Form 1:

        private void button1_Click(object sender, EventArgs e)
        { 
　　　　　　　//Pass SetValue to Form2 and let Form2 execute this method
            Form2 f2 = new Form2(SetValue);
            f2.Show();
        }
　　　　　//Method of assigning value to label2
        void SetValue(string str)
        {
            label2.Text = str;
        }

Code for Form 2:

        public delegate void del(string str);
        private del de1;
        public Form2 (del del)
        {
            this.de1 = del;
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.de1.Invoke(textBox1.Text.Trim());//The final execution here is the SetValue function of Form 1
        }

Form interface and execution result: