Saving a variable that gets loaded on program startup (WFA) C#

Question

The user is asked to type in the serial number on the device he's using. Then the program uses this serial number for all the functions. This was made so that the user can easily replace said device, without any technical help - just typing the new serial number in the application.

However, the way I've done it, the user needs to type in the serial number each time the program is opened, and it's kind of tedious.

Is there a way to store the last entered serial number, so that it loads the next time the program is being runned?

I have checked this link. While it seems promising, it hasn't solved the problem for me. I'll explain with my code below.

Here is the code asking for the user input serial number:

        byte[] xbee { get; set; }
        var xbee_serienr = prop1_serienr.Text;
        xbee = new byte[xbee_serienr.Length / 2];

        for (var i = 0; i < xbee.Length; i++)
        {
            xbee[i] = byte.Parse(xbee_serienr.Substring(i * 2, 2), NumberStyles.HexNumber);
        }

I tried the aforementioned link, and save it like so:

prop1_serienr    string     user    0013A20040A65E23

And then use it in the code like so:

    prop1_serienr = Xbee.Properties.Settings.Default.prop1_serienr;
    //keep in mind I made the silly decision using Xbee as namespace and xbee as a variable

But the prop1_serienr remains empty this way.

Any tips or guidelines on how to make this easier than having to type it every time the program starts would be greatly appreciated. If that's my only option I will resort to hard coding the serial numbers and then change the code every time a device is changed.

Answer 1

Hard coding the serial numbers is really not an option, especially when something as "saving a serial number" is not very complicated at all (but like all things, complicated it can be, if you let it).

The very easy approach:

public partial class Form1 : Form
{
    private byte[] _xbee;
    public Form1()
    {
        if (!File.Exists("serial.txt"))
        {
            File.Create("serial.txt");
        }
        else
        {
            _xbee = File.ReadAllBytes("serial.txt");
        }

        InitializeComponent();
    }

    private void btnSaveSerial_Click(object sender, EventArgs e)
    {
        byte[] xbee { get; set; }
        var xbee_serienr = prop1_serienr.Text;
        xbee = new byte[xbee_serienr.Length / 2];

        for (var i = 0; i < xbee.Length; i++)
        {
            xbee[i] = byte.Parse(xbee_serienr.Substring(i * 2, 2), NumberStyles.HexNumber);
        }

        _xbee = xbee;
        File.WriteAllBytes("serial.txt", xbee);
    }
}

It reads the bytes from the file at startup (if the file exists). It writes the bytes to the file when the user has changed the serial (and clicked on a button to save it).

As I've said, you can make this as easy or as complicated as you like, but this should get you going.