This tutorial will guide you through the steps of creating an Akonadi resource, an agent program which transports PIM data between the Akonadi system and a storage backend.
The resource developed in this tutorial will use a directory on the local file system as its backend and handle contact data, i.e. address book entries.
For other real-life examples of akonadi resources see projects in /kdepim/runtime/resources KDE source directory.
Warning
This section needs improvements: Please help us to
cleanup confusing sections and
fix sections which contain a todo
Add error handling to resource code snippets
Prerequisites
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This section needs improvements: Please help us to
cleanup confusing sections and
fix sections which contain a todo
Describe required versions and build setup
Preparation
The KDE client library for Akonadi provides a base class, Akonadi::ResourceBase, which already implements most of the low level communication between resource and Akonadi server, letting the resource developer concentrate on communication with the backend.
We can kick-start the resource by using KAppTemplate, which can be found as KDE template generator in the development section of the K-menu, or by running kapptemplate in a terminal window.
First, we select the Akonadi Resource Template in the C++ section of the program, give our project a name and continue through the following pages to complete the template creation.
A look at the generated project directory shows us the following files:
At this stage it is already possible to compile the resource, so we can already check if our development environment is setup correctly by creating the build directory and having CMake either generate Makefiles or a KDevelop project file.
Note: if after running cmake you receive error like: "Could NOT find KdepimLibs (missing: KdepimLibs_CONFIG)", try running cmake with additional parameter:
and open the generated project with KDevelop and run the build process from there.
Adjusting the resource description file
The capabilities of the resource need to be described in both human understable and machine interpretable form.
This is achieved through a so-called desktop file, similar to those installed by applications.
Since the vcarddirresource.desktop file generated by KAppTemplate contains only example values, we need to edit it:
[Desktop Entry]Name=Akonadi VCardDir ResourceComment=Resource for a directory containing contact data filesType=AkonadiResourceExec=akonadi_vcarddir_resourceIcon=text-directoryX-Akonadi-MimeTypes=text/directoryX-Akonadi-Capabilities=ResourceX-Akonadi-Identifier=akonadi_vcarddir_resource
Name and Comment are strings visible to the user and can be translated. Since our resource will serve contact data, the example valued for Icon and X-Akonadi-MimeTypes fields are conveniently correct.
Resource Configuration
Since the backend of our resource will be a file system directory, we need a way to let the user configure it and a way to persistantly store this configuration.
KDE has a nice framework for this called KConfig XT which enabled us developers to specify our config options as an XML file and have the code for storage and retrieval auto-generated.
The template we are basing our resource on already contains such a file, vcarddirresource.kcfg, and we only have to add a new option for our base directory:
To enable the user to change this properties, we need to create and show a config dialog. Since we are using KConfig XT this is pretty easy, but for the scope of this tutorial we make our lives even more easier and just use a KFileDialog
Warning
This simplification has the side effect that the passed window ID cannot be used as it should. See FAQ section at the end of the tutorial.
First we need to add two new include directives at the beginning of our source file vcarddirresource.cpp:
The call to synchronize at the end tells Akonadi to start retrieving the new data from our resource.
Tip
Since there can be more than one resource of a certain type, it is recommended to change the resource name to something that makes them distiguishable. In the case of this example resource it could be the name of the base directory or part of its path
Data Retrieval
In this section of the tutorial we will implement the data retrieval methods of our resource, i.e. the method which Akonadi will call to get the contact data our resource is providing.
Retrieving Collections
The first thing Akonadi will ask for are our collections. Resources can organize their data in a tree of collections, similar to how files are organized in a tree of directories on the file system.
For now we only want to support one directory so we only need one collection.
Tip
Exercise: Extend this to map a tree of vCard directories into Akonadi.
Retrieval of collections is handled in retrieveCollections:
The code creates a top level collection, i.e. its parent collection is Akonadi's root collection, sets the configured path as its remote identifier (so we could eventually map it back to our "backend" location) and uses our resource name as the user visible collection name.
Since our resource will be providing contact data, we need to set the respective MIME type to indicate which kind of data our collection will hold.
Finally the fully set up collection is sent to Akonadi.
Tip
You can customize visualization properties of the collection, e.g. icon, by using the EntityDisplayAttribute class
Retrieving Items
Retrieving items for a specific collection is similar to listing the files of a specific directory.
Conveniently our backend is a directory, so we can map this directly.
There are several methods to implement item retrieval, e.g. synchronous or asynchronous, all items in one go or in patches, etc.
For the scope of the tutorial we choose the easiest combination, i.e. synchronously provide all items in one go.
Tip
Exercise: Use KDirLister to do this asynchronously and in patches.
First we need another include directive:
#include<QtCore/QDir>
Then we implement retrieveItems:
voidVCardDirResource::retrieveItems(constAkonadi::Collection&collection){// our collections have the mapped path as their remote identifierconstQStringpath=collection.remoteId();QDirdir(path);QStringListfilters;filters<<QLatin1String("*.vcf");constQStringListfileList=dir.entryList(filters,QDir::Files);Item::Listitems;foreach(constQString&file,fileList){Itemitem(QLatin1String("text/directory"));item.setRemoteId(path+QLatin1Char('/')+file);items<<item;}itemsRetrieved(items);}
Our earlier decision to use the directory's path as the collection's remote identifier conveniently allows us to retrieve the path from the given collection.
We then list all vCard files in that directory and create one Akonadi item for each one, this time using the path plus the file's name as the remote identifier.
Note
This rather primitive implementation assumes that all files with the extension vcf are indeed vCard files and contain only one vCard each.
Finally the whole list of items is sent to Akonadi.
Retrieving Item Data
Continuing our file system analogy, retrieving a specific item's data is similar to reading a specific file's data or its associated meta data.
So we have again the convenience of a direct mapping between Akonadi and backend functionality.
Since our backend items are vCard files, we need to parse them into data structures which we can then use as item payloads.
Again aided by our decision what to use as the item's remote identifier, we can directly use it to open the respective vCard file.
After parsing the data we create a new item object, use the given item to initialize it, set the contact data object as its payload and send it to Akonadi.
Note
Since we need the full vCard data for parsing, we ignore the parts parameter and always retrieve the full payload.
Item Changes
All Akonadi clients, e.g. end user applications, agents, etc., can at any time add items to collections, change item data and remove items from collections. If such a change happens in the collection tree of a resource, the resource should properly make the respective change on its backend.
By default, resources are only notified about which items have been changed and which of the parts have been modified.
To automatically the get the updated payload we only have to enable this operation mode on the resource's change recorder.
This tells the base implementation that each item change should be fetched with full payload before delivering it to the methods covered in the following subsections.
Tip
Exercise: Add handling for collection changes, e.g. create subdirectories when child collections have been created.
Adding Items
On order to handle items being added to one of our collections, we need to implement the method itemAdded.
First we need another include directive for a helper class:
As usual we get the path of the directory a specific collection maps to from the collection's remote identifier.
Then we check if the newly added item is already equiped with a payload, in our case a KABC::Addressee object.
In either case we ensure that the object has an unique identifier by which we then use as the base name for the vCard file.
Finally we let Akonadi know that we have processed the item change and which remote identifier our backend has assigned to it.
Modifying Items
In our case handling item modifications is almost the same as handling item adding, however more sophisticated resource will most likely do different things depending on the parts parameter.
Of course changes to collections and items might also happen on the backend and in cases where the backend can send out change notifications, the resource can map these changes directly into its collection tree.
The APIs for that are exactly the same which any other client would use, i.e. Akonadi's job classes.
Tip
Exercise: Use KDirWatch to get notified about file and directory changes and modify the Akonadi storage accordingly.
Testing
The Akonadi Test Framework allows to create self-contained test environments so developers do not risk impacting their normal Akonadi setup.
To install new resource to system run (might need root):
make install
</syntaxhighlight>
or copy built files manually to the following locations:
$KDEDIRS/bin/akonadi_vcarddir_resource
$KDEDIRS/share/akonadi/agents/vcarddirresource.desktop
</syntaxhighlight>
where $KDEDIRS points to your KDE installation prefix.
Then run Akonadi Configuration (search by this keyword in kickoff launcher) and click "Add..." button to add new resource - new resource should be there; or in KAddressBook add new address book - new resource should be available as address book type (restarting akonadi server might help if it does not get into this list immediately).
Warning
This section needs improvements: Please help us to
cleanup confusing sections and
fix sections which contain a todo
as part of the resource's creation process: when the Akonadi control process creates a resource, it will also call the resource's configure() method through D-Bus once the resource has registered itself.
when another program explicitly requests it: since configure() is exposed as a D-Bus method, any other program can call it to request a resource's reconfiguration. End user applications might offer this functionality to allow the user to change resource specific settings.
What is the purpose of the window ID parameter of configure()?
The resource is a program on its own, i.e. it is not the same process as the end user application working with the data provided by the resource.
In an in-process scenario any configuration UI can specify one of the application's top level widgets as its parent, thus associating the configuration UI with that window.
Window managing systems such as KDE's KWin use this information to keep new windows from interrupting the user unless they are very likely a consequence of a user's action.
To make such an association across process boundaries, the calling application can send a platforms specific window identifier over to the resource which in tunr can then use it to specify it as a "parent" for its configuration UI like this:
