Gtk.Grid inside another grid not visible on window

I made a separate file for all the labels to be used in the main window called Labels.vala

Previously, I had created the labels inside the MainWindow.vala file, but now I wanted to make a separate file for the labels as the labels will change based on the location set by the user and that will make the code in the MainWindow.vala file too long.

This is the code inside the Labels.vala file:

Now, when I try to add this class to a grid inside the main window, it compiles with no errors but the labels are not displayed in the main window.

This is how I add the labels grid in the main window grid.

Link to source code: https://github.com/Suzie97/epoch

At the moment you're trying to attach an instance of the Labels class to the MainWindow grid, but you need to use the Labels.labels_grid property that it exposes.

grid.attach (labels.labels_grid, 0, 4, 1, 2);