GSettingsBackend

GSettingsBackend — Interface for settings backend implementations

Object Hierarchy

    GObject
    ╰── GSettingsBackend

Includes

#include <gio/gsettingsbackend.h>

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.

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.

Functions

g_settings_backend_get_default ()

GSettingsBackend *
g_settings_backend_get_default (void);

Returns the default GSettingsBackend. It is possible to override the default by setting the GSETTINGS_BACKEND environment variable to the name of a settings backend.

The user gets a reference to the backend.

Returns

the default GSettingsBackend.

[transfer full]

Since: 2.28


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 occurring 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.

Parameters

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.

Parameters

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.

Parameters

backend

a GSettingsBackend implementation

 

path

the path containing the changes

 

items

the NULL-terminated list of changed keys.

[array zero-terminated=1]

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.

Parameters

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.

Parameters

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().

Parameters

backend

a GSettingsBackend implementation

 

tree

a GTree containing the changes

 

origin_tag

the origin tag

 

Since: 2.26


g_settings_backend_flatten_tree ()

void
g_settings_backend_flatten_tree (GTree *tree,
                                 gchar **path,
                                 const gchar ***keys,
                                 GVariant ***values);

Calculate the longest common prefix of all keys in a tree and write out an array of the key names relative to that prefix and, optionally, the value to store at each of those keys.

You must free the value returned in path , keys and values using g_free(). You should not attempt to free or unref the contents of keys or values .

Parameters

tree

a GTree containing the changes

 

path

the location to save the path.

[out]

keys

the location to save the relative keys.

[out][transfer container][array zero-terminated=1]

values

the location to save the values, or NULL.

[out][optional][transfer container][array zero-terminated=1]

Since: 2.26


g_keyfile_settings_backend_new ()

GSettingsBackend *
g_keyfile_settings_backend_new (const gchar *filename,
                                const gchar *root_path,
                                const gchar *root_group);

Creates a keyfile-backed GSettingsBackend.

The filename of the keyfile to use is given by filename .

All settings read to or written from the backend must fall under the path given in root_path (which must start and end with a slash and not contain two consecutive slashes). root_path may be "/".

If root_group is non-NULL then it specifies the name of the keyfile group used for keys that are written directly below root_path . For example, if root_path is "/apps/example/" and root_group is "toplevel", then settings the key "/apps/example/enabled" to a value of TRUE will cause the following to appear in the keyfile:

1
2
[toplevel]
enabled=true

If root_group is NULL then it is not permitted to store keys directly below the root_path .

For keys not stored directly below root_path (ie: in a sub-path), the name of the subpath (with the final slash stripped) is used as the name of the keyfile group. To continue the example, if "/apps/example/profiles/default/font-size" were set to 12 then the following would appear in the keyfile:

1
2
[profiles/default]
font-size=12

The backend will refuse writes (and return writability as being FALSE) for keys outside of root_path and, in the event that root_group is NULL, also for keys directly under root_path . Writes will also be refused if the backend detects that it has the inability to rewrite the keyfile (ie: the containing directory is not writable).

There is no checking done for your key namespace clashing with the syntax of the key file format. For example, if you have '[' or ']' characters in your path names or '=' in your key names you may be in trouble.

Parameters

filename

the filename of the keyfile

 

root_path

the path under which all settings keys appear

 

root_group

the group name corresponding to root_path , or NULL.

[nullable]

Returns

a keyfile-backed GSettingsBackend.

[transfer full]


g_memory_settings_backend_new ()

GSettingsBackend *
g_memory_settings_backend_new (void);

Creates a memory-backed GSettingsBackend.

This backend allows changes to settings, but does not write them to any backing storage, so the next time you run your application, the memory backend will start out with the default values again.

Returns

a newly created GSettingsBackend.

[transfer full]

Since: 2.28


g_null_settings_backend_new ()

GSettingsBackend *
g_null_settings_backend_new (void);

Creates a readonly GSettingsBackend.

This backend does not allow changes to settings, so all settings will always have their default values.

Returns

a newly created GSettingsBackend.

[transfer full]

Since: 2.28

Types and Values

GSettingsBackend

typedef struct _GSettingsBackend GSettingsBackend;

An implementation of a settings storage repository.


struct GSettingsBackendClass

struct GSettingsBackendClass {
  GObjectClass parent_class;

  GVariant *    (*read)             (GSettingsBackend    *backend,
                                     const gchar         *key,
                                     const GVariantType  *expected_type,
                                     gboolean             default_value);

  gboolean      (*get_writable)     (GSettingsBackend    *backend,
                                     const gchar         *key);

  gboolean      (*write)            (GSettingsBackend    *backend,
                                     const gchar         *key,
                                     GVariant            *value,
                                     gpointer             origin_tag);
  gboolean      (*write_tree)       (GSettingsBackend    *backend,
                                     GTree               *tree,
                                     gpointer             origin_tag);
  void          (*reset)            (GSettingsBackend    *backend,
                                     const gchar         *key,
                                     gpointer             origin_tag);

  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);

  GVariant *    (*read_user_value)  (GSettingsBackend    *backend,
                                     const gchar         *key,
                                     const GVariantType  *expected_type);
};

Class structure for GSettingsBackend.

Members

read ()

virtual method to read a key's value

 

get_writable ()

virtual method to get if a key is writable

 

write ()

virtual method to change key's value

 

write_tree ()

virtual method to change a tree of keys

 

reset ()

virtual method to reset state

 

subscribe ()

virtual method to subscribe to key changes

 

unsubscribe ()

virtual method to unsubscribe to key changes

 

sync ()

virtual method to sync state

 

get_permission ()

virtual method to get permission of a key

 

read_user_value ()

virtual method to read user's key value

 

G_SETTINGS_BACKEND_EXTENSION_POINT_NAME

#define G_SETTINGS_BACKEND_EXTENSION_POINT_NAME "gsettings-backend"

Extension point for GSettingsBackend functionality.