The main source code for the application can be found in the ``main.py`` file within the ``src`` directory. The purpose of the other files is explained in other tutorials, such as the :ref:`First_Application` tutorial.
The Program
-----------
Most the code for the application is included in a single ``main.py`` file which contains a single ``Application`` class to manage the running of the application and a ``main`` function to start it.
Much of the is very similar to other examples and tutorials. We will focus on the parts that are specific to this example.
Relevant Modules
~~~~~~~~~~~~~~~~
Besides standard Python modules such as ``os`` and ``sys``, the ``Handy`` module helps us to create adaptive user interfaces. This module is imported in the same way as the ``Gtk`` module:
.. literalinclude:: app/src/main.py
:language: python3
:start-at: import os
:end-at: Pages
The ``widgets`` module contains a helper class that we won't cover in any detail.
Application Class
~~~~~~~~~~~~~~~~~
The ``Application`` class provides the usual methods to set up the application
and perform tasks when it is run.
In the ``do_startup`` method we define two parameters for the thumbnail dimensions:
.. literalinclude:: app/src/main.py
:language: python3
:start-at: do_startup
:end-at: thumbnail_height
These are hard-coded in this example, but more complex applications would load these values from the application's settings.
In the ``do_activate`` method we set up the user interface, using a helper class to set up an adaptive user interface consisting of two leaflets: one in the window's header bar; the other in the main area of the window:
.. literalinclude:: app/src/main.py
:language: python3
:start-at: do_activate
:end-at: show_all
The leaflet in the main area holds two pages: one with a list of thumbnails; the other with a simple image viewer. The ``do_activate`` method also calls the ``load_thumbnails`` method to load thumbnails for the images. This is described later.
Summary
-------
You can access files in specific directories in the user's home directory by calling the ``GLib.get_user_special_dir`` function to obtain the file paths you require. The directory you want to access is specified using a value from the ``GLib.UserDirectory`` enum.
In this case we use ``DIRECTORY_PICTURES`` to access the user's pictures directory and load images using the ``GdkPixbuf.Pixbuf`` class.
This example shows how to read image files from one of the user's directories and display their contents. When run, the application shows thumbnails of the images in a scrolling list. When a thumbnail is selected, a larger version of the images is displayed.
.. image:: images/screenshot.png
:scale: 50%
:align: center
:alt: A screenshot of the application running in the phone environment
We will focus on the parts of the application that are related to reading the image files and displaying their contents.
