.NET 4.x Отключение кнопки - C#

 private DateTime t;
        private DateTime i;
 
        private void button1_Click_1(object sender, EventArgs e)
        {
            try
            {
                t = Convert.ToDateTime(textBox1.Text);
                i = Convert.ToDateTime(textBox2.Text);
            }
            catch (FormatException)
            {
                button1.Enabled = false;
            }
            int o = 0;
            TimeSpan z = i - t;
            for (int r = 0; r <= z.Days; r++)
            {
                if (t.Day == 13)
                {
                    if (t.DayOfWeek.ToString() == "Friday")
                    {
                        o++;
                        t = t.AddDays(1);
                    }
                    else
                    {
                        t = t.AddDays(1);
                    }
                }
                else
                {
                    t = t.AddDays(1);
                }
            }
            label1.Text = o.ToString();

        }
 
        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            bool f = true;
            string h = Convert.ToString(textBox1.Text);
            string d = Convert.ToString(textBox2.Text);
            try
            {
                DateTime t = DateTime.Parse(h);
                DateTime i = DateTime.Parse(d);
 
            }
            catch (FormatException)
            {
                button1.Enabled = false;
                f = false;
            }
            if (f != false)
            {
                button1.Enabled = true;
            }