Understanding Widgets, Layouts & Templates
Getting up to speed with GNOME templates
Widgets are one of the most atomic components for GNOME. Everything you see on the screen in a GTK application is a widget. To create an application, we place a couple of widgets in a layout.
Button, Image, TextView, DrawingArea are some examples of widgets. Box and Grid are some examples of Layouts.
Let us have a look at what window.ui, Right click on window.ui and click on Open in > UI desiginer. This is what we have as of now
The default hello world template
The absolute parent component here is the Application window . Inside the application window, there is a HeaderBar component and a label component. The label component has a ID of label. ID is important as it serves as a pointer later on while writing code.
Let us have a look at what window.py contains
from gi.repository import Gtk
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@Gtk.Template(resource_path='/com/yourusername/splash/window.ui')
class SplashWindow(Gtk.ApplicationWindow):
__gtype_name__ = 'SplashWindow'
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label = Gtk.Template.Child()
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def __init__(self, **kwargs):
super().__init__(**kwargs)
The SplashWindow sub-classes Gtk.ApplicationWindow (Since the absolute parent component in the template is a Gtk.ApplicationWindow). The rule of thumb is that per template file, there will be one python class which sub-classes the absolute parent GTK type. The __gtype_name__ of the class should be the same as the ID of the parent component.
Gtk.Template.Child() is used to retrieve the widget whose ID is the same as the variable name. In our case, the label widget's ID is label. So label will be a widget whose class will be Gtk.Label.
This is the basic premise of templates in python.

Customizing the UI layout

Now that we understand the basics, we won't be needing any layouts since the UI for the application is very simple. Let us go back to the designer view for window.ui and
  • Remove the Gtk.Label and replace the label widget with Gtk.Image. Set the ID of the component to wallpaper_container.
  • Click on the headerbar and change the text from "Hello World" to "Splash". Make sure the ID of header bar is set to header_bar
  • In the options side bar when clicked on header_bar , change the last option (Number of Items) from 0 to 1. There will be an empty space which pops up to the left of the title of the header bar. Double click on the empty space and select Gtk.Button .
  • Set the ID of Gtk.Button to shuffle_button . Also set the text of the button to Shuffle
The modified version of the template
Let us add a menu button, later we can add a pop over menu which will contain an about button. On click will show the about dialog.
Let's get back to editing window.ui . Click on the header bar and in the properties sidebar, increment Number of items from 1 to 2. You will see a new blank space pop up.
Creating space for the menu button
Double click on empty space and add a Gtk.MenuButton. Go to the properties sidebar of the Gtk.MenuButton and set the ID of the button to menu_button.
Double click and add Gtk.Image. In the properties sidebar, Set the ID to open_menu_icon and Icon name to open-menu-symbolic.
Setting the menu icon on the button
Let us move the menu button to the other end. Having two buttons on the same side of the header bar is not good design. Click on the Menu button and go to the second tab in the properties sidebar (named child container properties). There is an option called Pack Type. This decides which side the widgets align. Change the Pack Type to End. You can see that the menu moved to the right end of the header bar.
Packing the button to the end
Let us add a loading spinner as well. So that whenever we are loading an wallpaper from the internet, we can use the spinner to indicate work being done on the background. Go back to the header bar and increment the Number of items to 3. Now again, double click on the empty space and add a Gtk.Spinner. On the properties side bar, set the ID to loading_spinner.
Adding the spinner
Looks good! Let us jump back to code and make use of this template as a base and build on top of it.
Do not forget to save and commit these changes to your git repository!
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