当适配器为空时，在微调器中设置提示

Question

当自定义适配器为空时，如何在Spinner中设置提示。

我的适配器列表：

public class DeviceAdapter extends ArrayAdapter<NetworkDevice> {

    public DeviceAdapter(Context context, List<NetworkDevice> devices) {
        super(context, R.layout.spinner_cell, devices);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        NetworkDevice device = getItem(position);
        if (convertView == null)
            convertView = LayoutInflater.from(getContext())
                    .inflate(R.layout.spinner_cell, null);

        TextView txtCurrentSpinnerCell = convertView.findViewById(R.id.txtSelectedServiceName);
        return convertView;
    }

    @Override
    public View getDropDownView(int position, View convertView, ViewGroup parent) {
        NetworkDevice device = getItem(position);
        if (convertView == null)
            convertView = LayoutInflater.from(getContext())
                    .inflate(R.layout.spinner_selection_cell, null);

        TextView txtSpinnerCell = convertView.findViewById(R.id.txtServiceName);
        txtSpinnerCell.setText(device.getName());
        TextView txtIpAddress = convertView.findViewById(R.id.txtIpAddress);
        txtIpAddress.setText(device.getIp());
        return convertView;
    }
}  

如何实施？任何想法...

提前谢谢。问候...）