Qt Contacts Overview
The Qt Contacts API enables a client to request contact data from local or remote backends in a platform-independent and datastore-agnostic manner. This is achieved by defining generic personal information data abstractions which can sufficiently describe contact data stored on any platform. Due to the cross-platform nature of the API, and the ability for developers to write platform-independent implementations of a QContactManager which may unify one or more platform-specific contact backends, it is intended that the semantics and quirks of the underlying datastores on any platform may be entirely opaque from the perspective of Qt-based, cross-platform client applications.
Contact information is stored in datastores whose functionality is exposed via a manager. The Qt Contacts API models a contact as a collection of distinct details. Individual contacts may be related to one other, and these relationships are stored separately from contacts themselves and may be manipulated directly by clients.
For a full list of classes, see Qt Contacts C++ Classes.
The client-facing API allows retrieval, modification and deletion of contacts, and relationships, as well as access to manager meta data and capability reporting.
Contact information is stored in container (value) classes. These classes are not derived from QObject, and hence can be used in lists. They do not have parents, do not emit signals, and so on. They represent data which may be manipulated and retrieved from a manager.
A contact is the digital representation of a person, group or entity, which is stored in a platform-specific manner. Information pertaining to a single contact may be located across several different datastores, and each datum (or detail) may or may not pertain to a particular context in which that information is valid. A contact may include semantically identical pieces of information that are relevant in different contexts. For example, a contact may have a phone number that is relevant to their home context, and another phone number that is relevant to their work context. It can be seen that the context of information defines its validity to the user, depending on the context of usage; and as such, the sum of information in a given context can be considered equivalent to a contextual identity. This allows great flexibility when consolidating data from various sources into a single, cohesive contact.
Each contact stored in a manager is identified by an id which consists of a manager identifier (URI) and the QContactId manager-local id which is used to identify the contact in that manager. Note that a contact stored in one manager may have the same local id as a different contact stored in another manager; please see the QContactId documentation for more information.
A detail is a single, cohesive unit of information that is stored in a contact. As explained previously, it is valid for a particular context or set of contexts. A detail may have specific metadata associated with it, such as its sub-type or context, as well as access constraints which may apply to the the detail (such as read-only, irremovable, etc).
There are a number of common details defined in the API which are intended for use by clients, as listed in Contact Details Leaf Classes.
Contacts may participate in relationships with other contacts. The details of any such relationship is stored by the manager which contains the contact. There are several standard relationship types supported by default, and arbitrary relationship types are also allowed if the manager supports that feature. One important relationship is that of group membership. Membership of a contact in a group can be modeled as that group contact participating in a
HasMember relationship with the contact.
Access to contacts is provided by implementations of the Qt Contacts manager API. A manager provides access to zero or more platform-specific datastores. Each datastore may support different capabilities (for example, the ability to store certain datatypes, the ability to natively filter on different details, the provision of locking mechanisms, the provision of changelog information, etc) which are reported by the manager on request. The manager therefore provides access to contacts and relationships stored in different datastores, in a platform and datastore independent manner.
Meta Data API
The API offered by the QContactManager exposes functionality which is implemented by plugins. These plugins may be platform specific, and may be provided by Nokia or by third party developers. As described above, each plugin will have different capabilities and implement the functionality exposed by the Qt Contacts API to a different degree.
The QContactManager class provides a static function QContactManager::availableManagers() which allows clients of the API to determine (at run time) which plugins (managers) are available for use.
Clients of the API also need to be able to determine (at run time) what the capabilities of a given plugin (contact manager) are. The QContactManager class provides an API to query the capabilities of a given manager with the following synchronous functions:
- isFilterSupported(const QContactFilter& filter) const
- isRelationshipTypeSupported(const QString& relationshipType, const QString& contactType = QContactType::TypeContact) const
- supportedDataTypes() const
- supportedContactTypes() const
A given manager is identified by its URI. The URI consists of the manager's name, any relevant parameters which were used during instantiation of the manager, and the version of the manager. While the name of the manager identifies the plugin which provides the functionality, you cannot guarantee that the data available through one manager will be available through another with the same name (for example, if one parameter tells the plugin to store and retrieve contact information from a particular online service or local file).
The synchronous API offered to allow run-time querying of a manager's metadata includes:
- managerName() const
- managerParameters() const
- managerUri() const
- managerVersion() const;
- (static) parseUri(const QString& uri, QString* managerName, QMap<QString, QString>* params)
- (static) buildUri(const QString& managerName, const QMap<QString, QString>& params, int implementationVersion = -1)
The functionality that the above functions provide is only available through synchronous API.
The asynchronous API provides a way to access or modify the contact information managed by a particular backend via non-blocking, asynchronous requests. It is recommended for most applications that the asynchronous API be used where possible.
The asynchronous API is offered through various classes derived from the QContactAbstractRequest class, including QContactIdFetchRequest, QContactFetchRequest, QContactSaveRequest, QContactRemoveRequest, QContactRelationshipFetchRequest, QContactRelationshipSaveRequest, and QContactRelationshipRemoveRequest.
The asynchronous API allows manipulation of contacts and contact relationships, but does not provide manager capability or meta data information reporting.
The synchronous API provides the simplest way to access or modify the contact information managed by a particular backend. It has the disadvantage that calls block the current thread of execution until completion and is therefore most suitable only for applications which interact with local, high-speed datastores, or for applications which do not require a responsive user interface.
The synchronous API is offered through the QContactManager class, and includes manipulation of contacts and contact relationships. As previously described, the meta data reporting and manipulation functions are also provided via synchronous API only.
Clients can perform actions on contacts which support them. Actions are things like Send Email or Dial, and can be provided from various sources including Qt Plugins or the Qt Service Framework. Every action implementation is uniquely identified by a combination of its name, the name of the service which provided the implementation, and the version of the implementation. These pieces of data may be encapsulated in a QContactActionDescriptor which can be used to retrieve an instance of the implementation from a QContactActionFactory.
Different actions will allow (or require) different parameters to invocation. For example, an action which allows clients to send emails to a contact may be able to accept attachments as a parameter to invocation. Each action must be invoked on an action target or list of targets, where a target may be a contact or a specific detail of a particular contact.
The non-client-facing API allows third party developers to implement a manager engine plugin from which clients may request data.
The functionality exposed by the QContactManager class may be implemented by engine plugins which interface directly to a platform-specific backend or provide their own data storage backend. As such, the terms manager, plugin and backend are used interchangeably in this documentation to refer to any engine plugin which implements the functionality exposed by the QContactManager interface. The plugin architecture allows dynamic loading of different manager engines at runtime.
A manager backend may be implemented by subclassing QContactManagerEngine, and providing a QContactManagerEngineFactory which can instantiate it when required.
For more information on the available engines and how to write your own engine, see Qt Contacts Manager Engines.