textbox values with sum display in other form

public class Form1 : Form
{
    private TextBox textBox1 = new TextBox();

    private Form2 form2 = new Form2();

    public Form1()
    {
        this.textBox1.Multiline = true;
        this.textBox1.Height = 100;
        this.textBox1.TextChanged += this.textBox1_TextChanged;

        this.Controls.Add(this.textBox1);
        this.Load += this.Form1_Load;
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        form2.Show();
    }

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        int sum = 0;

        foreach (string s in this.textBox1.Lines)
        {
            int v;

            if (int.TryParse(s, out v))
            {
                sum += v;
            }
        }

        form2.Sum = sum.ToString();
    }
}

public class Form2 : Form
{
    private TextBox textBox2 = new TextBox();

    public Form2()
    {
        this.Controls.Add(this.textBox2);
    }

    public string Sum
    {
        set { this.textBox2.Text = value; }
    }
}