GSettingsBackend

GSettingsBackend — an interface for settings backend implementations

Synopsis

#include <gio/gsettingsbackend.h>

                    GSettingsBackend;
                    GSettingsBackendClass;
#define             G_SETTINGS_BACKEND_EXTENSION_POINT_NAME
void                g_settings_backend_changed          (GSettingsBackend *backend,
                                                         const gchar *key,
                                                         gpointer origin_tag);
void                g_settings_backend_path_changed     (GSettingsBackend *backend,
                                                         const gchar *path,
                                                         gpointer origin_tag);
void                g_settings_backend_keys_changed     (GSettingsBackend *backend,
                                                         const gchar *path,
                                                         gchar const * const *items,
                                                         gpointer origin_tag);
void                g_settings_backend_path_writable_changed
                                                        (GSettingsBackend *backend,
                                                         const gchar *path);
void                g_settings_backend_writable_changed (GSettingsBackend *backend,
                                                         const gchar *key);
void                g_settings_backend_changed_tree     (GSettingsBackend *backend,
                                                         GTree *tree,
                                                         gpointer origin_tag);

void                g_settings_backend_setup            (const gchar *context,
                                                         GSettingsBackend *backend);
void                g_settings_backend_setup_keyfile    (const gchar *context,
                                                         const gchar *filename);

Object Hierarchy

  GObject
   +----GSettingsBackend

Properties

  "context"                  gchar*                : Read / Write / Construct Only

Description

The GSettingsBackend interface defines a generic interface for non-strictly-typed data that is stored in a hierarchy. To implement an alternative storage backend for GSettings, you need to implement the GSettingsBackend interface and then make it implement the extension point G_SETTINGS_BACKEND_EXTENSION_POINT_NAME.

The interface defines methods for reading and writing values, a method for determining if writing of certain values will fail (lockdown) and a change notification mechanism.

The semantics of the interface are very precisely defined and implementations must carefully adhere to the expectations of callers that are documented on each of the interface methods.

Some of the GSettingsBackend functions accept or return a GTree. These trees always have strings as keys and GVariant as values. g_settings_backend_create_tree() is a convenience function to create suitable trees.

Note

The GSettingsBackend API is exported to allow third-party implementations, but does not carry the same stability guarantees as the public GIO API. For this reason, you have to define the C preprocessor symbol G_SETTINGS_ENABLE_BACKEND before including gio/gsettingsbackend.h

Details

GSettingsBackend

typedef struct _GSettingsBackend GSettingsBackend;

An implementation of a settings storage repository.


GSettingsBackendClass

typedef struct {
  GObjectClass parent_class;

  gboolean      (*supports_context) (const gchar         *context);

  GVariant *    (*read)             (GSettingsBackend    *backend,
                                     const gchar         *key,
                                     const GVariantType  *expected_type,
                                     gboolean             default_value);
  gchar **      (*list)             (GSettingsBackend    *backend,
                                     const gchar         *path,
                                     gchar              **resets,
                                     gsize                n_resets,
                                     gsize               *length);
  gboolean      (*write)            (GSettingsBackend    *backend,
                                     const gchar         *key,
                                     GVariant            *value,
                                     gpointer             origin_tag);
  gboolean      (*write_keys)       (GSettingsBackend    *backend,
                                     GTree               *tree,
                                     gpointer             origin_tag);
  void          (*reset)            (GSettingsBackend    *backend,
                                     const gchar         *key,
                                     gpointer             origin_tag);
  void          (*reset_path)       (GSettingsBackend    *backend,
                                     const gchar         *path,
                                     gpointer             origin_tag);
  gboolean      (*get_writable)     (GSettingsBackend    *backend,
                                     const gchar         *key);
  void          (*subscribe)        (GSettingsBackend    *backend,
                                     const gchar         *name);
  void          (*unsubscribe)      (GSettingsBackend    *backend,
                                     const gchar         *name);
  void          (*sync)             (GSettingsBackend    *backend);

  GPermission * (*get_permission)   (GSettingsBackend    *backend,
                                     const gchar         *path);

  gpointer padding[7];
} GSettingsBackendClass;


G_SETTINGS_BACKEND_EXTENSION_POINT_NAME

#define G_SETTINGS_BACKEND_EXTENSION_POINT_NAME "gsettings-backend"

Extension point for GSettingsBackend functionality.


g_settings_backend_changed ()

void                g_settings_backend_changed          (GSettingsBackend *backend,
                                                         const gchar *key,
                                                         gpointer origin_tag);

Signals that a single key has possibly changed. Backend implementations should call this if a key has possibly changed its value.

key must be a valid key (ie: starting with a slash, not containing '//', and not ending with a slash).

The implementation must call this function during any call to g_settings_backend_write(), before the call returns (except in the case that no keys are actually changed and it cares to detect this fact). It may not rely on the existence of a mainloop for dispatching the signal later.

The implementation may call this function at any other time it likes in response to other events (such as changes occuring outside of the program). These calls may originate from a mainloop or may originate in response to any other action (including from calls to g_settings_backend_write()).

In the case that this call is in response to a call to g_settings_backend_write() then origin_tag must be set to the same value that was passed to that call.

backend :

a GSettingsBackend implementation

key :

the name of the key

origin_tag :

the origin tag

Since 2.26


g_settings_backend_path_changed ()

void                g_settings_backend_path_changed     (GSettingsBackend *backend,
                                                         const gchar *path,
                                                         gpointer origin_tag);

Signals that all keys below a given path may have possibly changed. Backend implementations should call this if an entire path of keys have possibly changed their values.

path must be a valid path (ie: starting and ending with a slash and not containing '//').

The meaning of this signal is that any of the key which has a name starting with path may have changed.

The same rules for when notifications must occur apply as per g_settings_backend_changed(). This call might be an appropriate reasponse to a 'reset' call but implementations are also free to explicitly list the keys that were affected by that call if they can easily do so.

For efficiency reasons, the implementation should strive for path to be as long as possible (ie: the longest common prefix of all of the keys that were changed) but this is not strictly required. As an example, if this function is called with the path of "/" then every single key in the application will be notified of a possible change.

backend :

a GSettingsBackend implementation

path :

the path containing the changes

origin_tag :

the origin tag

Since 2.26


g_settings_backend_keys_changed ()

void                g_settings_backend_keys_changed     (GSettingsBackend *backend,
                                                         const gchar *path,
                                                         gchar const * const *items,
                                                         gpointer origin_tag);

Signals that a list of keys have possibly changed. Backend implementations should call this if keys have possibly changed their values.

path must be a valid path (ie: starting and ending with a slash and not containing '//'). Each string in items must form a valid key name when path is prefixed to it (ie: each item must not start or end with '/' and must not contain '//').

The meaning of this signal is that any of the key names resulting from the contatenation of path with each item in items may have changed.

The same rules for when notifications must occur apply as per g_settings_backend_changed(). These two calls can be used interchangeably if exactly one item has changed (although in that case g_settings_backend_changed() is definitely preferred).

For efficiency reasons, the implementation should strive for path to be as long as possible (ie: the longest common prefix of all of the keys that were changed) but this is not strictly required.

backend :

a GSettingsBackend implementation

path :

the path containing the changes

items :

the NULL-terminated list of changed keys

origin_tag :

the origin tag

Since 2.26


g_settings_backend_path_writable_changed ()

void                g_settings_backend_path_writable_changed
                                                        (GSettingsBackend *backend,
                                                         const gchar *path);

Signals that the writability of all keys below a given path may have changed.

Since GSettings performs no locking operations for itself, this call will always be made in response to external events.

backend :

a GSettingsBackend implementation

path :

the name of the path

Since 2.26


g_settings_backend_writable_changed ()

void                g_settings_backend_writable_changed (GSettingsBackend *backend,
                                                         const gchar *key);

Signals that the writability of a single key has possibly changed.

Since GSettings performs no locking operations for itself, this call will always be made in response to external events.

backend :

a GSettingsBackend implementation

key :

the name of the key

Since 2.26


g_settings_backend_changed_tree ()

void                g_settings_backend_changed_tree     (GSettingsBackend *backend,
                                                         GTree *tree,
                                                         gpointer origin_tag);

This call is a convenience wrapper. It gets the list of changes from tree, computes the longest common prefix and calls g_settings_backend_changed().

backend :

a GSettingsBackend implementation

tree :

a GTree containing the changes

origin_tag :

the origin tag

Since 2.26


g_settings_backend_setup ()

void                g_settings_backend_setup            (const gchar *context,
                                                         GSettingsBackend *backend);

Sets up backend for use with GSettings.

If you create a GSettings with its context property set to context then it will use the backend given to this function. See g_settings_new_with_context().

The backend must be set up before any settings objects are created for the named context.

It is not possible to specify a backend for the default context.

This function takes a reference on backend and never releases it.

context :

a context string (not NULL or "")

backend :

a GSettingsBackend

Since 2.26


g_settings_backend_setup_keyfile ()

void                g_settings_backend_setup_keyfile    (const gchar *context,
                                                         const gchar *filename);

Sets up a keyfile for use with GSettings.

If you create a GSettings with its context property set to context then the settings will be stored in the keyfile at filename. See g_settings_new_with_context().

The keyfile must be setup before any settings objects are created for the named context.

It is not possible to specify a keyfile for the default context.

If the path leading up to filename does not exist, it will be recursively created with user-only permissions. If the keyfile is not writable, any GSettings objects created using context will return FALSE for any calls to g_settings_is_writable() and any attempts to write will fail.

context :

a context string (not NULL or "")

filename :

a filename

Since 2.26

Property Details

The "context" property

  "context"                  gchar*                : Read / Write / Construct Only

The "context" property gives a hint to the backend as to what storage to use. It is up to the implementation to make use of this information.

E.g. DConf supports "user", "system", "defaults" and "login" contexts.

If your backend supports different contexts, you should also provide an implementation of the supports_context() class function in GSettingsBackendClass.

Default value: ""

See Also

GSettings, GIOExtensionPoint