private void button1_Click(object sender, EventArgs e)
{
    ListPerson listPerson = new ListPerson();
    listPerson.ShowDialog();
    textBox1.Text = listPerson.infoPersonDataGridView.CurrentRow.Cells[0].Value
    + "," + listPerson.infoPersonDataGridView.CurrentRow.Cells[1].Value + ", " +
    listPerson.infoPersonDataGridView.CurrentRow.Cells[2].Value;
}