The gio.settings.Settings class provides a convenient API for storing and retrieving
application settings.
Reads and writes can be considered to be non-blocking. Reading
settings with gio.settings.Settings is typically extremely fast: on
approximately the same order of magnitude (but slower than) a
glib.hash_table.HashTable lookup. Writing settings is also extremely fast in
terms of time to return to your application, but can be extremely expensive
for other threads and other processes. Many settings backends
(including dconf) have lazy initialisation which means in the common
case of the user using their computer without modifying any settings
a lot of work can be avoided. For dconf, the D-Bus service doesn’t
even need to be started in this case. For this reason, you should
only ever modify gio.settings.Settings keys in response to explicit user action.
Particular care should be paid to ensure that modifications are not
made during startup — for example, when setting the initial value
of preferences widgets. The built-in gio.settings.Settings.bind
functionality is careful not to write settings in response to notify signals
as a result of modifications that it makes to widgets.
When creating a gio.settings.Settings instance, you have to specify a schema
that describes the keys in your settings and their types and default
values, as well as some other information.
Normally, a schema has a fixed path that determines where the settings
are stored in the conceptual global tree of settings. However, schemas
can also be ‘relocatable’, i.e. not equipped with
a fixed path. This is
useful e.g. when the schema describes an ‘account’, and you want to be
able to store a arbitrary number of accounts.
Paths must start with and end with a forward slash character (/)
and must not contain two sequential slash characters. Paths should
be chosen based on a domain name associated with the program or
library to which the settings belong. Examples of paths are
/org/gtk/settings/file-chooser/ and /ca/desrt/dconf-editor/.
Paths should not start with /apps/, /desktop/ or /system/ as
they often did in GConf.
Unlike other configuration systems (like GConf), GSettings does not
restrict keys to basic types like strings and numbers. GSettings stores
values as glib.variant.VariantG, and allows any glib.variant_type.VariantType for
keys. Key names are restricted to lowercase characters, numbers and -.
Furthermore, the names must begin with a lowercase character, must not end
with a -, and must not contain consecutive dashes.
Similar to GConf, the default values in GSettings schemas can be
localized, but the localized values are stored in gettext catalogs
and looked up with the domain that is specified in the
gettext-domain attribute of the <schemalist> or <schema>
elements and the category that is specified in the l10n attribute of
the <default> element. The string which is translated includes all text in
the <default> element, including any surrounding quotation marks.
The l10n attribute must be set to messages or time, and sets the
[locale category for
translation](https://www.gnu.org/software/gettext/manual/html_node/Aspects.html#index-locale-categories-1).
The messages category should be used by default; use time for
translatable date or time formats. A translation comment can be added as an
XML comment immediately above the <default> element — it is recommended to
add these comments to aid translators understand the meaning and
implications of the default value. An optional translation context
attribute can be set on the <default> element to disambiguate multiple
defaults which use the same string.
For example:
<!-- Translators: A list of words which are not allowed to be typed, in
GVariant serialization syntax.
See: https://developer.gnome.org/glib/stable/gvariant-text.html --><defaultl10n='messages'context='Banned words'>['bad', 'words']</default>
Translations of default values must remain syntactically valid serialized
glib.variant.VariantGs (e.g. retaining any surrounding quotation marks) or
runtime errors will occur.
GSettings uses schemas in a compact binary form that is created
by the `glib-compile-schemas`
utility. The input is a schema description in an XML format.
A DTD for the gschema XML format can be found here:
gschema.dtd
The `glib-compile-schemas` tool expects schema
files to have the extension .gschema.xml.
At runtime, schemas are identified by their ID (as specified in the
id attribute of the <schema> element). The convention for schema
IDs is to use a dotted name, similar in style to a D-Bus bus name,
e.g. org.gnome.SessionManager. In particular, if the settings are
for a specific service that owns a D-Bus bus name, the D-Bus bus name
and schema ID should match. For schemas which deal with settings not
associated with one named application, the ID should not use
StudlyCaps, e.g. org.gnome.font-rendering.
<schemalist><schemaid="org.gtk.Test"path="/org/gtk/Test/"gettext-domain="test"><keyname="greeting"type="s"><defaultl10n="messages">"Hello, earthlings"</default><summary>A greeting</summary><description>
Greeting of the invading martians
</description></key><keyname="box"type="(ii)"><default>(20,30)</default></key><keyname="empty-string"type="s"><default>""</default><summary>Empty strings have to be provided in GVariant form</summary></key></schema></schemalist>
An example for ranges, choices and enumerated types:
Default values are defined in the schemas that get installed by
an application. Sometimes, it is necessary for a vendor or distributor
to adjust these defaults. Since patching the XML source for the schema
is inconvenient and error-prone,
`glib-compile-schemas` reads so-called ‘vendor
override’ files. These are keyfiles in the same directory as the XML
schema sources which can override default values. The schema ID serves
as the group name in the key file, and the values are expected in
serialized glib.variant.VariantG form, as in the following example:
[org.gtk.Example]
key1='string'
key2=1.5
glib-compile-schemas expects schema files to have the extension
.gschema.override.
This makes it very easy to hook up a preferences dialog to the
underlying settings. To make this even more convenient, GSettings
looks for a boolean property with the name sensitivity and
automatically binds it to the writability of the bound setting.
If this ‘magic’ gets in the way, it can be suppressed with the
gio.types.SettingsBindFlags.NoSensitivity flag.
A relocatable schema is one with no path attribute specified on its
<schema> element. By using gio.settings.Settings.newWithPath, a gio.settings.Settings
object can be instantiated for a relocatable schema, assigning a path to the
instance. Paths passed to gio.settings.Settings.newWithPath will typically be
constructed dynamically from a constant prefix plus some form of instance
identifier; but they must still be valid GSettings paths. Paths could also
be constant and used with a globally installed schema originating from a
dependency library.
For example, a relocatable schema could be used to store geometry information
for different windows in an application. If the schema ID was
org.foo.MyApp.Window, it could be instantiated for paths
/org/foo/MyApp/main/, /org/foo/MyApp/document-1/,
/org/foo/MyApp/document-2/, etc. If any of the paths are well-known
they can be specified as <child> elements in the parent schema, e.g.:
GSettings comes with autotools integration to simplify compiling and
installing schemas. To add GSettings support to an application, add the
following to your configure.ac:
GLIB_GSETTINGS
In the appropriate Makefile.am, use the following snippet to compile and
install the named schema:
No changes are needed to the build system to mark a schema XML file for
translation. Assuming it sets the gettext-domain attribute, a schema may
be marked for translation by adding it to POTFILES.in, assuming gettext
0.19 is in use (the preferred method for translation):
GSettings will use gettext to look up translations for the <summary> and
<description> elements, and also any <default> elements which have a
l10n attribute set. Translations must not be included in the .gschema.xml
file by the build system, for example by using intltool XML rules with a
.gschema.xml.in template.
If an enumerated type defined in a C header file is to be used in a GSettings
schema, it can either be defined manually using an <enum> element in the
schema XML, or it can be extracted automatically from the C header. This
approach is preferred, as it ensures the two representations are always
synchronised. To do so, add the following to the relevant Makefile.am:
gsettings_ENUM_NAMESPACE specifies the schema namespace for the enum files,
which are specified in gsettings_ENUM_FILES. This will generate a
org.foo.MyApp.enums.xml file containing the extracted enums, which will be
automatically included in the schema compilation, install and uninstall
rules. It should not be committed to version control or included in
EXTRA_DIST.
The gio.settings.Settings class provides a convenient API for storing and retrieving application settings.
Reads and writes can be considered to be non-blocking. Reading settings with gio.settings.Settings is typically extremely fast: on approximately the same order of magnitude (but slower than) a glib.hash_table.HashTable lookup. Writing settings is also extremely fast in terms of time to return to your application, but can be extremely expensive for other threads and other processes. Many settings backends (including dconf) have lazy initialisation which means in the common case of the user using their computer without modifying any settings a lot of work can be avoided. For dconf, the D-Bus service doesn’t even need to be started in this case. For this reason, you should only ever modify gio.settings.Settings keys in response to explicit user action. Particular care should be paid to ensure that modifications are not made during startup — for example, when setting the initial value of preferences widgets. The built-in gio.settings.Settings.bind functionality is careful not to write settings in response to notify signals as a result of modifications that it makes to widgets.
When creating a gio.settings.Settings instance, you have to specify a schema that describes the keys in your settings and their types and default values, as well as some other information.
Normally, a schema has a fixed path that determines where the settings are stored in the conceptual global tree of settings. However, schemas can also be ‘relocatable’, i.e. not equipped with a fixed path. This is useful e.g. when the schema describes an ‘account’, and you want to be able to store a arbitrary number of accounts.
Paths must start with and end with a forward slash character (/) and must not contain two sequential slash characters. Paths should be chosen based on a domain name associated with the program or library to which the settings belong. Examples of paths are /org/gtk/settings/file-chooser/ and /ca/desrt/dconf-editor/. Paths should not start with /apps/, /desktop/ or /system/ as they often did in GConf.
Unlike other configuration systems (like GConf), GSettings does not restrict keys to basic types like strings and numbers. GSettings stores values as glib.variant.VariantG, and allows any glib.variant_type.VariantType for keys. Key names are restricted to lowercase characters, numbers and -. Furthermore, the names must begin with a lowercase character, must not end with a -, and must not contain consecutive dashes.
Similar to GConf, the default values in GSettings schemas can be localized, but the localized values are stored in gettext catalogs and looked up with the domain that is specified in the gettext-domain attribute of the <schemalist> or <schema> elements and the category that is specified in the l10n attribute of the <default> element. The string which is translated includes all text in the <default> element, including any surrounding quotation marks.
The l10n attribute must be set to messages or time, and sets the [locale category for translation](https://www.gnu.org/software/gettext/manual/html_node/Aspects.html#index-locale-categories-1). The messages category should be used by default; use time for translatable date or time formats. A translation comment can be added as an XML comment immediately above the <default> element — it is recommended to add these comments to aid translators understand the meaning and implications of the default value. An optional translation context attribute can be set on the <default> element to disambiguate multiple defaults which use the same string.
For example:
Translations of default values must remain syntactically valid serialized glib.variant.VariantGs (e.g. retaining any surrounding quotation marks) or runtime errors will occur.
GSettings uses schemas in a compact binary form that is created by the `glib-compile-schemas` utility. The input is a schema description in an XML format.
A DTD for the gschema XML format can be found here: gschema.dtd
The `glib-compile-schemas` tool expects schema files to have the extension .gschema.xml.
At runtime, schemas are identified by their ID (as specified in the id attribute of the <schema> element). The convention for schema IDs is to use a dotted name, similar in style to a D-Bus bus name, e.g. org.gnome.SessionManager. In particular, if the settings are for a specific service that owns a D-Bus bus name, the D-Bus bus name and schema ID should match. For schemas which deal with settings not associated with one named application, the ID should not use StudlyCaps, e.g. org.gnome.font-rendering.
In addition to glib.variant.VariantG types, keys can have types that have enumerated types. These can be described by a <choice>, <enum> or <flags> element, as seen in the second example below. The underlying type of such a key is string, but you can use gio.settings.Settings.getEnum, gio.settings.Settings.setEnum, gio.settings.Settings.getFlags, gio.settings.Settings.setFlags access the numeric values corresponding to the string value of enum and flags keys.
An example for default value:
An example for ranges, choices and enumerated types:
Vendor overrides
Default values are defined in the schemas that get installed by an application. Sometimes, it is necessary for a vendor or distributor to adjust these defaults. Since patching the XML source for the schema is inconvenient and error-prone, `glib-compile-schemas` reads so-called ‘vendor override’ files. These are keyfiles in the same directory as the XML schema sources which can override default values. The schema ID serves as the group name in the key file, and the values are expected in serialized glib.variant.VariantG form, as in the following example:
glib-compile-schemas expects schema files to have the extension .gschema.override.
Binding
A very convenient feature of GSettings lets you bind gobject.object.ObjectG properties directly to settings, using gio.settings.Settings.bind. Once a gobject.object.ObjectG property has been bound to a setting, changes on either side are automatically propagated to the other side. GSettings handles details like mapping between gobject.object.ObjectG and glib.variant.VariantG types, and preventing infinite cycles.
This makes it very easy to hook up a preferences dialog to the underlying settings. To make this even more convenient, GSettings looks for a boolean property with the name sensitivity and automatically binds it to the writability of the bound setting. If this ‘magic’ gets in the way, it can be suppressed with the gio.types.SettingsBindFlags.NoSensitivity flag.
Relocatable schemas
A relocatable schema is one with no path attribute specified on its <schema> element. By using gio.settings.Settings.newWithPath, a gio.settings.Settings object can be instantiated for a relocatable schema, assigning a path to the instance. Paths passed to gio.settings.Settings.newWithPath will typically be constructed dynamically from a constant prefix plus some form of instance identifier; but they must still be valid GSettings paths. Paths could also be constant and used with a globally installed schema originating from a dependency library.
For example, a relocatable schema could be used to store geometry information for different windows in an application. If the schema ID was org.foo.MyApp.Window, it could be instantiated for paths /org/foo/MyApp/main/, /org/foo/MyApp/document-1/, /org/foo/MyApp/document-2/, etc. If any of the paths are well-known they can be specified as <child> elements in the parent schema, e.g.:
Build system integration
GSettings comes with autotools integration to simplify compiling and installing schemas. To add GSettings support to an application, add the following to your configure.ac:
In the appropriate Makefile.am, use the following snippet to compile and install the named schema:
No changes are needed to the build system to mark a schema XML file for translation. Assuming it sets the gettext-domain attribute, a schema may be marked for translation by adding it to POTFILES.in, assuming gettext 0.19 is in use (the preferred method for translation):
Alternatively, if intltool 0.50.1 is in use:
GSettings will use gettext to look up translations for the <summary> and <description> elements, and also any <default> elements which have a l10n attribute set. Translations must not be included in the .gschema.xml file by the build system, for example by using intltool XML rules with a .gschema.xml.in template.
If an enumerated type defined in a C header file is to be used in a GSettings schema, it can either be defined manually using an <enum> element in the schema XML, or it can be extracted automatically from the C header. This approach is preferred, as it ensures the two representations are always synchronised. To do so, add the following to the relevant Makefile.am:
gsettings_ENUM_NAMESPACE specifies the schema namespace for the enum files, which are specified in gsettings_ENUM_FILES. This will generate a org.foo.MyApp.enums.xml file containing the extracted enums, which will be automatically included in the schema compilation, install and uninstall rules. It should not be committed to version control or included in EXTRA_DIST.