SUSI Linux app provides access to SUSI on Linux distributions on desktop as well as hardware devices like Raspberry Pi. It started off as a headless client but we decided to add a minimalist GUI to SUSI Linux for performing login and configuring settings. Since, SUSI Linux is a Python App, it was desirable to use a GUI Framework compatible with Python. Many popular GUI frameworks now provide bindings for Python. Some popular available choices are:
wxPython: wxPython is a Python GUI framework based on wxWidgets, a cross-platform GUI library written in C++. In addition to the standard dialogs, it includes a 2D path drawing API, dockable windows, support for many file formats and both text-editing and word-processing widgets. wxPython though mainly support Python 2 as programming language.
PyQT: Qt is a multi-licensed cross-platform framework written in C++. Qt needs a commercial licence for use but if application is completely Open Source, community license can be used. Qt is an excellent choice for GUIs and many applications are based on it.
PyGTK / PyGObject: PyGObject is a Python module that lets you write GUI applications in GTK+. It provides bindings to GObject, a cross platform C library. GTK+ applications are natively supported in most distros and you do not need to install any other development tools for developing with PyGTK.
Comparing all these frameworks, PyGTK was found to meet our needs very well. To make UIs in PyGTK, you have a WYSIWYG (What you see is what you get) editor called Glade. Though you can design whole UI programmatically, it is always convenient to use an editor like Glade to simplify the creation and styling of widgets.
To create a UI, you need to install Glade in your specific distribution. After that open glade, and add a Top Level container Window or AppWindow to your app.
Once that is done, you may pick from the available Layout Managers. We are using BoxLayout Manager in SUSI Linux GUIs. Once that is done, add your widgets to the Application Window using Drag and Drop.
Properties of widgets are available on the right panel. Edit your widget properties to give them meaningful IDs so we can address them later in our code. GTK also provides Signals for signaling about a events associated with the widgets. Open the Signals tab in the Widget properties pane. Then, you need to write name of the signal handler for the events associated with Widgets. A signal handler is a function that is fired upon the occurrence of the associated event. For example, we have signals like text_changed in Text Entry boxes, and clicked for Button.
After completing the design of GUI, we can address the .glade file of the UI we just created in the Python code. We can do this using the following snippet.
import gi gi.require_version('Gtk', '3.0') from gi.repository import Gtk builder = Gtk.Builder() builder.add_from_file("glade_files/signin.glade")
You can reference each widget from the Glade file using its ID like below.
email_field = builder.get_object("email_field")
Now, to handle all the declared signals in the Glade file, we need to make a Handler class. In this class, you need to define call the valid callbacks for your signals. On the occurrence of the signal, respective callback is fired.
class Handler: def onDeleteWindow(self, *args): Gtk.main_quit(*args) def signInButtonClicked(self, *args): # implementation def input_changed(self, *args): # implementation
We may associate a handler function to more than one Signal. For that, we just need to specify the respective function in both the Signals.
Now, we need to connect this Handler to builder signals. This can be done using the following line.
Now, we can show our window using the following lines.
The above lines displays the window and start the Gtk main loop. The script waits on the Gtk main loop. The app may be quitted using the Gtk.main_quit() call. Running this script shows the Login Screen of our app like below.
- PyGTK 3 Tutorial: https://python-gtk-3-tutorial.readthedocs.io/en/latest/
- Glade usage tutorial: https://prognotes.net/2015/06/gtk-3-c-program-using-glade-3/
- GTK+ 3 Reference Manual: https://developer.gnome.org/gtk3/stable