WinForm remember password function

Remember the password ：

         Dictionary<string, User> users = new Dictionary<string, User>();
        // Remember the password 
        private void Password()
        {
            // Create... Under the execution directory data.bin file , Used to store account and password 
            FileStream fs = new FileStream("data.bin", FileMode.Create);
            BinaryFormatter bf = new BinaryFormatter();
            // The account number is automatically saved 
            user.LoginID = txt_UserID.Text.Trim();
            // If checked, remember password , Just save the password , Otherwise, save the null value 
            if (CB_Rpwd.Checked)
            {
                user.Pwd = txt_Password.Text.Trim();
            }
            else
            {
                user.Pwd = "";
            }
            if (users.ContainsKey(user.LoginID))
            {
                users.Remove(user.LoginID);
            }
            users.Add(user.LoginID, user);
            bf.Serialize(fs, users);
            fs.Close();
            this.Dispose();
        }

Enter the account number and bring out the password automatically ：

         private void txt_UserID_SelectedIndexChanged(object sender, EventArgs e)
        {
            FileStream fs = new FileStream("data.bin", FileMode.OpenOrCreate);
            if (fs.Length > 0)
            {
                BinaryFormatter bf = new BinaryFormatter();
                users = bf.Deserialize(fs) as Dictionary<string, User>;

                for (int i = 0; i < users.Count; i++)
                {
                    if (txt_UserID.Text.Trim() != "")
                    {
                        if (users.ContainsKey(txt_UserID.Text.Trim()) && users[txt_UserID.Text].Pwd != "")
                        {
                            txt_Password.Text = users[txt_UserID.Text].Pwd;
                            CB_Rpwd.Checked = true;
                        }
                        else
                        {
                            txt_Password.Text = "";
                            CB_Rpwd.Checked = false;
                        }
                    }
                }
            }
            fs.Close();
        }

load Function to load data.bin Inside user Drop down of

  private void Frm_Login_Load(object sender, EventArgs e)
        {
            FileStream fs = new FileStream("data.bin", FileMode.OpenOrCreate);
            if (fs.Length > 0)
            {
                BinaryFormatter bf = new BinaryFormatter();
                users = bf.Deserialize(fs) as Dictionary<string, User>;
                foreach (User user in users.Values)
                {
                    txt_UserID.Properties.Items.Add(user.LoginID);
                }
                //for (int i = 0; i < users.Count; i++)
                //{
                //    if (txt_UserID.Text.Trim() != "")
                //    {
                //        if (users.ContainsKey(txt_UserID.Text.Trim()))
                //        {
                //            txt_Password.Text = users[txt_UserID.Text].Pwd;
                //            CB_Rpwd.Checked = true;
                //        }
                //    }
                //}
            }
            fs.Close();
        }