private void button3_Click(object sender, EventArgs e) { if (comboBox1.SelectedItem != null) { DeviceItem item = (DeviceItem)comboBox1.SelectedItem; DeviceListener.Device d = deviceListener.Find(item.id); if (d != null) { int ret = deviceListener.SDCardGetInfo(d, out string disk_size, out string free_size); if (ret == 0) { label4.Text = disk_size; label5.Text = free_size; } } } }