Low-level Activity API

Most activities will use the Python API to implement activities. This page will document the underlying mechanism that non-Python activities need to conform to.

This documentation effort was started by Bert while implementing the Squeak-based Etoys activity. Please fill in missing pieces and correct mistakes!

Overview

An Activity Bundle can specify an executable in the activity.info's exec field. When installing the bundle, the path of this executable will be expanded and added to the list of DBus services in $HOME/.local/share/dbus-1/services/ using the DBus service name as specified in the service_name field. When launching an activity from Sugar shell, a request to that DBus service is made, which makes DBus run the previously specified executable. The executable must create a "factory service" on the DBus using the specified service name.

The factory service provides a org.laptop.ActivityFactory.create() method which spawns an activity instance. Each activity instance has a unique activity_id which is passed as one of the parameters to the create() method.

Each activity instance opens an X window. This window must have two string properties, _SUGAR_BUNDLE_ID specifying the service name and _SUGAR_ACTIVITY_ID which is the id that was passed to create(). The instance registers a DBus object at /org/laptop/Activity/id where id is the decimal XID of the window. This object must implement the org.laptop.Activity interface.

When the last activity instance exits, the factory service should quit.

Activity Factory

Service name: my.organization.MyActivity (from activity bundle info file)

Object path: /my/organization/MyActivity (derived from service name)

Interface: org.laptop.ActivityFactory

org.laptop.ActivityFactory.create(params)

The create() method creates a new Activity instance. That instance is exposed on the DBus as /org/laptop/Activity/123456 where the number 123456 is the instance's top-level window XID.

The params dictionary can have the following entries:

activity_id

unique id for the activity to be created

pservice_id

identity of the sharing service for this activity in the PresenceService

object_id

identity of the journal object associated with the activity. When you resume an activity from the journal the object_id will be passed in (see datastore).

uri

URI associated with the activity. Used when opening an external file or resource in the activity, rather than a journal object (downloads stored on the file system for example or web pages)

Activity Instance

Service name: org.laptop.Activity6f7f3acacca87886332f50bdd522d805f0abbf1f (where 6f7f3acacca87886332f50bdd522d805f0abbf1f is the activity id)

Object path: /org/laptop/Activity/6f7f3acacca87886332f50bdd522d805f0abbf1f (where 6f7f3acacca87886332f50bdd522d805f0abbf1f is the activity id)

Interface: org.laptop.Activity

X Properties

The activity instance needs to set some properties on its top-level window:

_SUGAR_BUNDLE_ID 

The bundle id (e.g., my.organization.MyActivity) of type STRING.

_SUGAR_ACTIVITY_ID 

The activity id (e.g., 6f7f3acacca87886332f50bdd522d805f0abbf1f) of type STRING.

_NET_WM_NAME

should be set to the current activity title. It usually corresponds to the title which is displayed in the journal and advertised on the network for shared activities. See Freedesktop specification.

Methods

An activity instance needs to support the following methods:

org.laptop.Activity.set_active(active)

Activate or passivate an activity. Passive activities must release resources like sound, camera etc.

There used to be more methods but the API evolved so only this single one is remaining for now.

Datastore

An Activity instance must store its complete state in the central datastore so it appears in the Journal and can be resumed later. It needs to connect to the datastore service:

Service name: org.laptop.sugar.DataStore
Object path:  /org/laptop/sugar/DataStore
Interface:    org.laptop.sugar.DataStore

Keeping and Resuming

An item in the datastore is referenced by an object_id, it has a dictionary of properties, and possibly a file. The properties have String keys but Variant values. Here are a few properties:

'activity':          'my.organization.MyActivity'
'activity_id':       '6f7f3acacca87886332f50bdd522d805f0abbf1f'
'title':             'My new project'
'title_set_by_user': '0' 
'keep':              '0'
'ctime':             '1972-05-12T18:41:08'                    #created
'mtime':             '2007-06-16T03:42:33'                    #modified
'buddies':           array of buddies                         #not spec'ed yet
'preview':           base64(png file data, 300x225 px)        #temporarily Base64, will be a ByteArray
'icon-color':        '#ff0000,#ffff00'
'mime_type':         'application/x-my-activity'
'summary:text':      'text I want to be indexed'              #properties with key ending in ":text" will be searched in fulltext search

To create an item in the datastore, call create():

object_id = datastore.create(properties, filename)

If filename is not empty, the file will be copied to the datastore. The activity should delete the file once the call completes. The returned id will be a string like '4543af91-7be9-404e-b2f1-3e27cb15a15d'.

To update an item use update():

datastore.update(object_id, properties, filename)

Again, if a filename was given, it should be deleted when the call returns.

To retrieve an object's properties and file:

properties = datastore.get_properties(object_id)
filename = datastore.get_filename(object_id)

The returned temp file should be deleted by the activity as soon as possible, latest when the activity quits.

Querying

Activities may query the datastore:

(results,count) = datastore.find(query)

It returns the results as array of properties and a count of matching items (the array may have less items if the query was limited). In addition to the usual metadata items, the properties will include the object id at key 'uid', the mountpoint of the item at key 'mountpoint', and possibly a 'filename' if requested.

The query can be a:

string: fulltext search

the given string is searched in all text properties

dictionary: structured query

the key-value pairs in the dictionary specify the value (or array of values, or dictionary specifying range) for a specific property, e.g.:

'title' = 'First Project'

'mime_type' = ['image/png', 'image/jpeg']

'mtime' = {'start' = '2007-07-01T00:00:00', 'end' = '2007-08-01T00:00:00'}

also, there are a few specific keys to adjust the query:

'query': fulltext search term

'order_by': key (or array of keys) to order results by, to reverse order use '-key'

'limit', 'offset': return only limit results starting at offset

'mountpoints': array of mountpoint ids to search (or all if not specified)

'include_files': if true, generate files as if get_filename() had been called for each item. In results, a property 'filename' will be added.

You can also retrieve an array of unique values for a field:

values = datastore.get_uniquevaluesfor(property, query)

Note that currently (2007-07-25) the query is ignored in this call, it looks for all values in all entries.

Mount Points

Devices are represented as mount points in the datastore. If no mountpoint is explicitely specified, the main datastore (Journal) is used.

  mounts = datastore.mounts()

Returns an array of mount point descriptiors where each descriptor is a dictionary containing at least the following keys:

'id': the id used to refer explicitly to the mount point

'title': Human readable identifier for the mountpoint

'uri': The uri which triggered the mount

Mount points can be specified when creating an object (using a 'mountpoint' key and id value in the properties), and when querying the datastore (by adding a 'mountpoints' query option).

Example

[Activity]
name = My Activity
activity_version = 1
host_version = 1
service_name = my.organization.MyActivity
icon = activity-my
exec = myactivityfactory
show_launcher = yes

create factory service at my.organization.MyActivity

Signal /org/freedesktop/DBus org.freedesktop.DBus.NameAcquired(':1.23')

Signal /org/freedesktop/DBus org.freedesktop.DBus.NameAcquired('my.organization.MyActivity')

MethodCall /my/organization/MyActivity org.freedesktop.DBus.Introspectable.Introspect()

MethodCall /my/organization/MyActivity org.laptop.ActivityFactory.create(activity_id='6f7f3acacca87886332f50bdd522d805f0abbf1f')

launch new activity instance

create X window with _SUGAR_BUNDLE_ID='my.organization.MyActivity' and _SUGAR_ACTIVITY_ID='6f7f3acacca87886332f50bdd522d805f0abbf1f'

create instance dbus service at org.laptop.Activity6f7f3acacca87886332f50bdd522d805f0abbf1f

Signal /org/freedesktop/DBus org.freedesktop.DBus.NameAcquired(':1.24')

Signal /org/freedesktop/DBus org.freedesktop.DBus.NameAcquired('org.laptop.Activity6f7f3acacca87886332f50bdd522d805f0abbf1f')