delegate void TodoInvoke(string msg);

private void Todo(string msg)
{
    textBox1.Text = msg;
}

private void btn1_Click(object sender, EventArgs e)
{
    Thread thread = new Thread(() =>
    {
        this.Invoke(new TodoInvoke(Todo), "mzwu.com");
    });
    thread.Start();
}

private void btn1_Click(object sender, EventArgs e)
{
    Thread thread = new Thread(() =>
    {
        this.Invoke(new Action<string>(delegate (string msg) { textBox1.Text = msg; }), "mzwu.com");
    });
    thread.Start();
}