Saving Application Data

We now have a full GTK application working! For many applications, though, storing user data is critical for functionality. A common example might be reopening the data or file that was in use before the application previously exited.

Converting Data

Let's start with a simple data object. This will store the last used file by the user.

let lastUsedFile = {
    fileName: "/file/path/is/here",
    fileDescription: "this is a description of the file"
};

We first need to convert it to JSON for storage. GJS has built-in functions for this:

let dataJSON = JSON.stringify(lastUsedFile);

Locating Where To Save Data

Now we need to save dataJSON. Applications typically store data in their local configuration directory. You may know this as ~/.config/example-application/ but it varies on some systems so we should always use GLib's APIs to find it.

let dataDir = GLib.get_user_config_dir();

Now that we have the directory, we can build the storage path.

let destination = GLib.build_filenamev([dataDir, 'example-application', 'lastFile.json']);

This code builds the destination path string. We use GLib.build_filenamev to handle special cases where simple / strings don't work!

Always look for official APIs to handle file names!

Saving Data To A File

Now let's finish up by actually writing to the file.

let destinationFile = Gio.File.new_for_path(destination);

if (GLib.mkdir_with_parents(destinationFile.get_parent().get_path(), PERMISSIONS_MODE) === 0) {
    let [success, tag] = file.replace_contents(dataJSON, null, false, Gio.FileCreateFlags.REPLACE_DESTINATION, null);

    if(success) {
        /* it worked! */
    } else {
        /* it failed */
    }
} else {
     /* error */
}

This code comes from GIO File Operations.

And it is saved!