Pritesh Tupe

In the previous part, we built the UI for a user to enter fuel logs. But wait, where are we saving them? We aren’t. Let’s fix that in this part.

Check out the previous part where we built our UI here: Part 2

Where shall we store our data?

Instead of adding a database as most apps tend to do, we’ll be saving our logs in a humble (csv) file. Why? Because we don’t really need a database, that’s why. We won’t be saving millions of rows, nor do we need super-fast convoluted queries.

For saving to a file, Fyne has a convenient storage package. Go through it once; it’s not too long. Don’t worry, I’ll wait…

…

Done? Cool. Let’s go ahead and create a file to store our logs.

If you have your editor open on main.go file, add the following:

// import "fyne.io/fyne/v2/storage"

func main() {
  // ...
  w := a.NewWindow("Duri")

  // ---------- //

  logFileURL := storage.NewFileURI("./fuellogs.csv")

  logFile, err := storage.Appender(logFileURL)
  if err != nil {
    log.Fatalln(err)
  }
  defer logFile.Close()

  // ---------- //

  odoInput := widget.NewEntry()
  // ...
}

With NewFileURI we created a persistent storage for our fuel logs, in an eponymous fuellogs.csv in the app directory.

Notice the Appender function - it means the file is open in append-only mode. No data will be updated/removed, only added. This should be enough for now, although it does mean we won’t be able to remove or modify fuel logs once entered. Yet.

Always ensure all errors are handled and resources are freed up.

Now, to actually add the fuel log into our file. Replace the code inside OnSubmit; create a byte dump instead and write it into the csv file:

// import "fmt"

OnSubmit: func() {
  dump := fmt.Appendf(make([]byte, 0), "%s,%s,%s\n", odoInput.Text, fuelInput.Text, dateInput.Text)
  _, err = logFile.Write(dump)
  if err != nil {
    log.Fatalln(err)
  }
}

The Write function of our Appender takes in a slice of bytes. Which we supply using the Appendf function of fmt package in the std-lib.

Go ahead and go run .. Add a couple of fuel logs. You should see a fuellogs.csv (well, it’ll be created immediately on app start) with the data you entered. In my case, it looked like so:

200,12.24,02/11/2025
300,12.27,03/11/2025

Don’t worry about the unused FuelLog struct and the conversion functions. That will be helpful when we parse the data back.

If you cannot shake off your worry though, feel free to write a method that returns a []byte slice for FuelLog type, so we reuse the previous fl instance instead of creating a dump separately.

Regardless, that is enough for this part. Checkout everything that changed from the previous part on Github Diff.

We now have a input page that saves data persistently! In the next part, let’s figure out how to get it back and shown in the UI.

Building an Android App in Go using Fyne - Part 3: Storage

Where shall we store our data?