[Evolution-hackers] Calendars and Tasks integration

[Ettore Perazzoli <ettore ximian com>]

While finishing the initial work for integrating the calendar into the
new UI/shell framework (http://codeblogs.ximian.com/blogs/evolution has
screenshots), I have realized we might have overlooked the basic issue
with how to integrate the calendar and task list in the calendar view.

In Evo 1.4 the task list at the right of the calendar view just displays
the contents of the task list folder.  However, this doesn't fly very
well with the new model, since we are trying to move away from the
concept of a "default" folder and we're encouraging the user to use
multiple folders and use them at the same time instead.

So, what are we going to show there exactly?

The simple way to do it would be to do it like Apple iCal does it; you
just integrate calendars and tasks in the same object.  I.e. you don't
have "calendar" or "tasks" folders, but you just have "calendar and
tasks" folders that can contain both.

This model is nice, because tasks and calendars tend to be related to
each other and having just one entity makes it simpler for the user. 
E.g. if you create a "Personal" calendar and a "Work" calendar then you
automatically have "Personal" and "Work" categories in your task list as
well.

Also this removes the problem with what to display there altogether: you
just display the events and tasks from the same calendar, and the
selection in the sidebar on the left applies to both calendar and tasks.

On the other hand, there might be a few issues with this:

      * Connectors.  In Exchange, for example, tasks and calendars are
        different entities, so how are we going to make the two models
        go together?  We could just list everything as calendar folders,
        although "task" type folders would only have task items in them
        and "calendar" type folders would only have calendar items in
        them.  Then we would have to prevent the user from shooting
        herself in the foot by adding items to the wrong item (i.e.
        appointments to a task only folder or tasks to a calendar only
        folder)...  A bit messy, but it might work.

      * UI.  We still want to have the task-only table-based list;
        however, it might not make sense as a stand-alone component
        anymore.  Maybe we could have a button (in the toolbar?) to
        switch to tasks-only mode when you are in the calendar?  Then
        you could use the same button to switch back to
        calendar-and-tasks mode.

      * API issues.  Should we still distinguish tasks and calendars in
        the API?  I guess we could make it possible to have both a task
        folder and a calendar folder at the same URI, but then does it
        make sense that the API makes a difference between them?

Alternatively, we could keep the current way, i.e. keep calendars and
tasks separate components and have a way to select which tasks are being
shown in the taskbar on the right.  However, I am afraid this might turn
into an even bigger mess, since the user model would be more
complicated, we would require the user to configure more stuff, etc.

(For the record, on Outlook XP they pretty much keep doing it the old
way...)

Thoughts?

-- Ettore