- Qt 5.0
- Qt Versit Plugins
- Qt 5.0.0 Reference Documentation

# Qt Versit Plugins

While the QtVersit API provides a convenient way to import and export vCards, it is common to encounter domain-specific vCard properties that the Versit importer and exporter classes don't support. While it would be convenient if the base Versit module could support everything, that is not possible because there may be properties with the same name that have different semantics in different domains.

## Local Extension with Handlers

To remedy this, some hooks are provided to allow clients to alter the behaviour of QVersitContactImporter and QVersitContactExporter. The basic mechanisms that allow this are the QVersitContactImporterPropertyHandlerV2 and the QVersitContactExporterDetailHandlerV2 interfaces. A client can supplement the importer and exporter classes by implementing these interfaces and associating them using QVersitContactImporter::setPropertyHandler() and QVersitContactExporter::setDetailHandler().

## Global Extension with Plugins

While these interfaces allow a single client to supplement the behaviour of import and export, there are many cases where the entire deployment of the Versit library will be operating under a known context. For example, the library might be deployed on a device on a particular network where all of its peers are known to support certain properties. In this situation, it's desirable for all clients of the Versit library on that device to support those properties through the Qt Versit API. It is possible to extend the library globally by installing plugins that provide handlers automatically to all users of the library on the system.

Writing a plugin involves these steps:

- Implement a handler class that inherits from QVersitContactHandler.
- Implement a plugin class that inherits from QObject and QVersitContactHandlerFactory and implements the createHandler() function to create the handler class.
- Include the following two lines at the top of the factory declaration:

       Q_OBJECT
       Q_INTERFACES(QtVersit::QVersitContactHandlerFactory)

- Export the plugin using the Q_EXPORT_PLUGIN2 macro.
- Build the plugin using a suitable `.pro` file.
- Deploy the plugin in the `plugins/versit` directory.

Please see the relevant documentation in Qt for more details on writing a plugin.

### Example Plugin: Backup and Restore

A plugin is provided with the Qt Versit module that provides backup and restore functionality to the exporter and importer.

These can be used by creating the exporter and importer under the "backup" profile:

     QVersitContactExporter exporter(QVersitContactHandlerFactory::ProfileBackup);

     QVersitContactImporter importer(QVersitContactHandlerFactory::ProfileBackup);

When applied to the exporter, this handler encodes all writable details that the exporter doesn't recognise. The format it uses to encode the detail is as follows:

- All generated properties will have the name X-NOKIA-QCONTACTFIELD
- All generated properties will have a single Versit group, and all properties generated from a single detail will have the same group.
- All generated properties will have at least the parameters DETAIL, which holds the definition name of the QContactDetail from which it was generated, and FIELD, which holds the name of the field within the detail from which it was generated.
- If the field is of type QString or QByteArray, the property's value is set directly to the value of the field. (For a QByteArray value, the QVersitWriter will base-64 encode it.)
- If the field is of type bool, int, uint, QDate, QTime, QDateTime or QUrl a the property's value is set to a string representation of the field. A parameter DATATYPE is added to the property with value BOOL, INT, UINT, DATE, TIME or DATETIME depending on the type.
- If the field is of some other type, the field value is encoded to a QByteArray via QDataStream (and the resulting byte array is base-64 encoded by the QVersitWriter). In this case, the parameter DATATYPE=VARIANT is added to the Versit property.

For example, a detail with definition name "Pet" and fields "Name"="Rex" and "Age"=(int)14 will be exported to the vCard properties:

     G0.X-NOKIA-QCONTACTFIELD;DETAIL=Pet;FIELD=Name:Rex
     G0.X-NOKIA-QCONTACTFIELD;DETAIL=Pet;FIELD=Age;DATATYPE=INT:14

And the next detail (say, "Pet" with a field "Name"="Molly" will generate:

     G1.X-NOKIA-QCONTACTFIELD;DETAIL=Pet;FIELD=Name:Molly

When applied to the importer, this handler decodes the properties that were generated by the exporter under the backup profile.

The code for this plugin can be perused in the `plugins/versit/backuphandler` directory.