What I have learned

This is a kind of general report of SoC. The idea is to share all the things I have done until now, what I have learned.


I had a pretty good idea of what I wanted to do, just didn't know how to do it yet. My idea for what I was planning to do you can read here.
At this point I thought if I was going to work with Geoclue I would get my hands into it. I took some time to read about Geoclue, see how it works, its properties, learn about the providers, get up to date with it.
So my first step was compiling Geoclue. I dind't have any trouble compiling Geoclue, I had to compile Gypsy first to have that provider and I also had to install some developer packages (I use Ubuntu and except for Gypsy they were all in the repositories).
I checked the examples that were provided with Geoclue but they were all written in C. They where a good help to see how the different providers worked.

I was also reading about SoC and looking into the community. IRC was a starting point and it was easy to talk to other people there. At this point I was receiving lots of e-mails on the SoC list, hundreds of e-mails a day and of course I wanted to read all of them. I confess, it wasn't possible. I started to filter the important ones and reading those only. Only after a few weeks was I able to read all or most of all the e-mail.


By the end of the "bonding with the community" period I started to code. Lionel (my mentor) was excited in seeing some code and I also wanted to "get my hands dirty" so I started to code some examples in python to show and learn how Geoclue could be used. This wasn't that easy at start because I had never used D-Bus and there were no Geoclue + python examples available.
I went to google and quickly found this python-dbus tutorial. I also had to go thru the Geoclue API (D-BUS). I then managed to make some examples, four to be exact that are available here.
I learned the importance of the Geoclue Master provider, internally the Master provider uses the best Geoclue provider (based on client requirements and provider availability, accuracy and resource requirements). The provider that is actually used may change over time as conditions change, but the client can just ignore this. This was exactly what I wanted.

I was prepared to start changing GTG! and had a (more) serious meeting with Lionel to discuss how this would be done. It was his idea and he suggested a plugin. Of course to do the plugin the plugin support needed to be done. This would be good for me as I had never done such a thing and for GTG! that would be supporting plugins.

So I started to implement the plugin system/engine on GTG!. This was hard at start because I didn't understand how a plugin system worked and I didn't find nothing explaining, generically, how these systems worked. I did in fact find some specific information that helped me:

These two pages helped allot, I had a better idea but I was still a little confused on how the plugin would change the GTK+ interface. The answer was easier than I imagined and I took more time searching and looking into other applications code trying to understand this. I also got a precious help from Jonathan Barnoud (aka Pititjo) who mailed me some info and pointed me in the right direction for importing python files as modules.

The Plugin Engine

The general understanding of a plugin engine wasn't a problem, but the specific understanding of how plugins would interact with GTK+ was hard for me. At the end it was allot easier than I initially thought.
A plugin engine has to load plugins, that's the idea right?! The first thing is to decide how these plugins are going to be structured. GTG! is written in python and the contributers are python developers so it only made sense for the plugins to be python modules.
So I decided that the plugins for GTG! would have the following structure/properties:

  • A plugin can have several classes, even several files but there is only one main class to the plugin and that is the class that handles the plugin. The difference between the main class and the others is that the main class has the following properties:
    • PLUGIN_NAME - Defines the plugin name.
    • PLUGIN_AUTHORS - Defines the plugin authors
    • PLUGIN_VERSION - Defines the plugin version
    • PLUGIN_DESCRIPTION - Defines the plugin description
    • PLUGIN_ENABLED - A boolean, that defines the default state of the plugin (enabled/disabled)
  • A plugin has three mandatory methods, all plugins must have these methods, even if they aren't needed! All three methods receive a plugin api object as a parameter (I'll explain it down the way).
    • activate - This method will be executed when a plugin is activated. It will interact with the main GTG! window (TaskBrowser) and when the plugins are enabled they will be activated during the GTG! load (TaskBrowser load). It will also be executed when a plugin is activated during GTG! use.

    • deactivate - This method will be executed when a plugin is deactivated/disabled. It should reverse all changes that a plugin has done to GTG!.
    • onTaskOpened - GTG! has a additional "challange", the TaskEditor. When a task is opened GTG! opens a new window (TaskEditor) and this window is also a target for a plugin. So this method will be executed when a task is opened and the plugin api methods will reflect on this window.

    • A simple example:

   1 class ExamplePlugin:
   2     PLUGIN_NAME = 'Example'
   3     PLUGIN_AUTHORS = 'Paulo Cabido <paulo.cabido@gmail.com>'
   4     PLUGIN_VERSION = '0.1'
   5     PLUGIN_DESCRIPTION = 'Plugin Description goes here.'
   6     PLUGIN_ENABLED = True
   8     def activate(self, plugin_api):
   9         pass
  11     def onTaskOpened(self, plugin_api):
  12         pass
  14     def deactivate(self, plugin_api):
  15         pass

The plugin engine handles the loading of the modules and also the unloading (when a plugin is deactivated) and when it should happen. The LoadPlugins method does the tricky part. As I mentioned before, Jonathan Barnoud pointed me in the right way. He mailed me the code (those three lines of the first for) that would load python files as modules. The modules pkgutil and imp are used to discover modules in the plugins directory.

   1  def LoadPlugins(self):
   2         plugins = {}
   3         try:
   4             for loader, name, ispkg in pkgutil.iter_modules(self.plugin_path):
   5                 file, pathname, desc = imp.find_module(name, self.plugin_path)
   6                 plugins[name] = imp.load_module(name, file, pathname, desc)
   7         except Exception, e:
   8             print "Error: %s" % e
  10         for name, plugin in plugins.items():
  11             self.Plugins.append(self.loadPlugin(plugin))
  13         return self.Plugins

I have talked about the plugins, how they are structured, how they are loaded but another important part is how they interact with GTG!. This is done thru the Plugin API. It would be easy to pass the GTK+ window to the plugin and let the plugin developers do what they want, but that's not a very good practice. So I created this API, that has the methods that the plugins can use to interact with GTG!. The API supports the following methods:

  • AddMenuItem(item) - Adds a menu item to the main GTG! window's menu bar, under Plugins.

  • RemoveMenuItem(item) - Removes a a menu item from the Plugin menu, at the menu bar.

  • AddToolbarItem(item) - Adds a button to the main GTG! toolbar.

  • RemoveToolbarItem(item) - Removes a button from the main GTG! toolbar.

  • AddTaskToolbarItem(item) - Adds a button to the task editor's toolbar.

  • getRequester() - Returns the requester object.
  • changeTaskTreeStore(treestore) - Changes the tree store. This method was created to let plugin developers create new views for tasks.
  • add_tag(tag) - Adds a tag to a task. This method is intended to be used within the task editor.
  • add_tag_attribute(tag, attribute_name, attribute_value) - Adds a new attribute (and value) to a task. It appends the tag to the end of the task.
  • get_tags() - Retrieves all tags of a task. This method is also intended to be used within the task editor.
  • get_textview() - Passes the task editor's textview.

The API is a work in progress and things may change with time, some methods can be altered and some new ones can be included. If you have any suggestions, feel free to let me know.

The last part there is to talk about is the Plugin Manager. This is the GUI to select witch plugins are enabled or disabled. The manager uses the engine to activate/deactivate the plugins. It is accessible under the Plugin menu (Preferences).


I have mentioned the examples I made to show how Geoclue can be used. After writing those examples, I decided to write a module to help python developers use Geoclue.
The idea of the module is to facilitate as much as possible, for a developer to use Geoclue without having to reinvent the wheel or help a developer who lacks the time to learn about Geoclue from zero. This way the only thing a developer needs is to import the module on their project and with a minimum code effort they can get addresses and positions.
While coding this module (and the examples also) I learned about Geoclue and D-Bus, witch I had never used. It's really easy to use.
I also used signal/slots for the first time with the traditional connect(function) method. This way it's possible to detect changes to the address or position and automatically process those changes. I thought about using D-Bus to make this but my idea was to have as less dependencies as possible for the programmer.
Currently this module is working with the following features:

  • init() - I separated this from the init to be possible to use the Signals before any addresses or positions where detected.

  • set_requirements(accuracy, time, require_updates, allowed_resources) - Changes the requirements for the provider.
  • get_location_info() - Returns the variable (dictionary) with the location info (position and address). The values may vary with different providers.
  • get_available_providers() - Returns a List of the available providers and witch services each provider supports.
  • set_position_provider(provider) - Changes the position provider to a given provider.
  • set_address_provider(provider) - Changes the address provider to a given provider.
  • get_position_provider() - Returns the current position provider.
  • get_address_provider() - Returns the current address provider.
  • connect(function) and disconnect(function) - Connect or Disconnect (a already connect) function to handle changes on the location variable.
  • compare_position(latitude, longitude, proximity_factor) – compares two positions, a given one and the actual position to see if they are the same or near by. The range is defined by the proximity_factor.
  • reverse_position(latitude, longitude, accuracy) – Reverses a position to a address.

There is a test file in the test folder that I created to show how to use each of these features. You can see for yourselves how easy it is to use Geoclue now!
Any suggestion or idea, as usual, is welcome.


I have also learned allot about Getting Things Gnome!. It is a well structured application with a high potential!
As you know, Getting Things Gnome! is an organizer for the GNOME desktop environment. You create tasks to organize what you have to do and each task can have subtasks and so on. For a task to be completed all the subtasks (if they exist) also have to be completed. GTG! has a view called "Work View" that lists the tasks that are possible to be completed at that moment. So if a task with several subtasks exists, the subtasks have to be completed before the main task will appear in the "Work View". This is a great concept that lets one keep in mind the priority of the tasks that are to be done.

So how does GTG! work?

  • backend - The current implementation of the backend is the localfile (only existing backend for now). Tasks will be stored in a XML file.
  • The core module, 'core' in GTG/ is the heart of the application and it contains:
    • the datastore synchronizes itself, on each start, with the backend. It contains a list of tasks (objects).
    • the requester. Because nothings interacts directly with the datastore, each interface uses the requester to translate/control the requests before sending them to the datastore. Only the requester can interact directly with the datastore.
    • task - It's a object with attributes (duedate, title, tags, parent, child, etc). The parent and child attributes define if a task is a subtask of another task. Each task has a tid (task id) and the tid is represented for example like 7@1. 7 is the task's number and 1 is number of the backend.
    • tags - Tags are also objects with attributes. The tags attributes are extensible. A tag is represented by "@tag" and an attribute example is color (witch has a value associated).
  • TaskBrowser - It's the main GTG! window. When starting it asks the requester for a list of tasks, they are then displayed.

  • TaskEditor - It's the particular view of a task.

Apps/GTG/soc/whatihavelearned (last edited 2015-01-06 10:33:37 by OliverPropst)