private void button1_Click(object sender, EventArgs e) { SelectProcessForm spf = new SelectProcessForm(); DialogResult dr = spf.ShowDialog(); if (DialogResult.OK == dr) { if (!spf.SelectedProcess.Equals(String.Empty)) { if (textBox1.Text.Equals(String.Empty)) { textBox1.Text = spf.SelectedProcess; } else { textBox1.Text = String.Format("{0}, {1}", textBox1.Text, spf.SelectedProcess); } } } }