Can you connect an Android Xamarin App, to sql server directly or is it necessary to consume some WebApi or some other way?

I'm starting in the mobile app, and I have an App that needs to bring all the data from sql server "online", I tried to connect the App to the sql server as if it were a WinForm, and when it is connected to the PC the test smartphone and start debugging, correctly select, insert, update, etc, but when I disconnect it from the pc, and open the App, I want to make a select, and does not do the App, as if it does not was connecting to SQL, is there any different way to connect the App to SQL Server? Here I have an example that I have in the App about a login that I made, and that works for me only when the test smartphone is connected to the PC

 ConexionController con = new ConexionController();
        cTripleDES decry = new cTripleDES();
        SqlConnection miConexion =new SqlConnection( "data source = snare.arvixe.com; initial catalog=logins; user id=******; password= ******");
        public int Login(string user, string password)
        {
            try
            {   
                if (miConexion.State == ConnectionState.Closed)
                {
                    miConexion.Open();
                }
                SqlCommand comando = new SqlCommand("select email, clave from CrmCustomers where email = '" + user + "'and clave = '" + password + "' ", miConexion);
                comando.ExecuteNonQuery();
                DataSet ds = new DataSet();
                SqlDataAdapter da = new SqlDataAdapter(comando);
                da.Fill(ds, "CrmCustomers");
                DataRow DR;
                DR = ds.Tables["CrmCustomers"].Rows[0];
                if ((user == DR["email"].ToString()) && (password == DR["clave"].ToString()))
                {
                    miConexion.Close();
                    return 1;
                }
                else
                {
                    miConexion.Close();
                    return 2;
                }

            }
            catch (Exception ex)
            {
                miConexion.Close();
                return 3;
            }
        }