mirror of
https://gitlab.gnome.org/GNOME/glib.git
synced 2024-11-10 19:36:18 +01:00
157f80c244
The GSettings migration docs had a link to the no-longer existing gsettings-tutorial branch of gnome-utils. Remove it. https://bugzilla.gnome.org/show_bug.cgi?id=690043
516 lines
23 KiB
XML
516 lines
23 KiB
XML
<chapter>
|
|
<title>Migrating from GConf to GSettings</title>
|
|
|
|
<section>
|
|
<title>Before you start</title>
|
|
|
|
<para>
|
|
Converting individual applications and their settings from GConf to
|
|
GSettings can be done at will. But desktop-wide settings like font or
|
|
theme settings often have consumers in multiple modules. Therefore,
|
|
some consideration has to go into making sure that all users of a setting
|
|
are converted to GSettings at the same time or that the program
|
|
responsible for configuring that setting continues to update the value in
|
|
both places.
|
|
</para>
|
|
<para>
|
|
It is always a good idea to have a look at how others have handled
|
|
similar problems before.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Conceptual differences</title>
|
|
|
|
<para>
|
|
Conceptually, GConf and GSettings are fairly similar. Both
|
|
have a concept of pluggable backends. Both keep information
|
|
about keys and their types in schemas. Both have a concept of
|
|
mandatory values, which lets you implement lock-down.
|
|
</para>
|
|
<para>
|
|
There are some differences in the approach to schemas. GConf
|
|
installs the schemas into the database and has API to handle
|
|
schema information (gconf_client_get_default_from_schema(),
|
|
gconf_value_get_schema(), etc). GSettings on the other hand
|
|
assumes that an application knows its own schemas, and does
|
|
not provide API to handle schema information at runtime.
|
|
GSettings is also more strict about requiring a schema whenever
|
|
you want to read or write a key. To deal with more free-form
|
|
information that would appear in schema-less entries in GConf,
|
|
GSettings allows for schemas to be 'relocatable'.
|
|
</para>
|
|
<para>
|
|
One difference in the way applications interact with their
|
|
settings is that with GConf you interact with a tree of
|
|
settings (ie the keys you pass to functions when reading
|
|
or writing values are actually paths with the actual name
|
|
of the key as the last element. With GSettings, you create
|
|
a GSettings object which has an implicit prefix that determines
|
|
where the settings get stored in the global tree of settings,
|
|
but the keys you pass when reading or writing values are just
|
|
the key names, not the full path.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>GConfClient (and GConfBridge) API conversion</title>
|
|
|
|
<para>
|
|
Most people use GConf via the high-level #GConfClient API.
|
|
The corresponding API is the #GSettings object. While not
|
|
every GConfClient function has a direct GSettings equivalent,
|
|
many do:
|
|
<table id="gconf-client-vs-gsettings">
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row><entry>GConfClient</entry><entry>GSettings</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row><entry>gconf_client_get_default()</entry><entry>no direct equivalent,
|
|
instead you call g_settings_new() for the schemas you use</entry></row>
|
|
<row><entry>gconf_client_set()</entry><entry>g_settings_set()</entry></row>
|
|
<row><entry>gconf_client_get()</entry><entry>g_settings_get()</entry></row>
|
|
<row><entry>gconf_client_get_bool()</entry><entry>g_settings_get_boolean()</entry></row>
|
|
<row><entry>gconf_client_set_bool()</entry><entry>g_settings_set_boolean()</entry></row>
|
|
<row><entry>gconf_client_get_int()</entry><entry>g_settings_get_int()</entry></row>
|
|
<row><entry>gconf_client_set_int()</entry><entry>g_settings_set_int()</entry></row>
|
|
<row><entry>gconf_client_get_float()</entry><entry>g_settings_get_double()</entry></row>
|
|
<row><entry>gconf_client_set_float()</entry><entry>g_settings_set_double()</entry></row>
|
|
<row><entry>gconf_client_get_string()</entry><entry>g_settings_get_string()</entry></row>
|
|
<row><entry>gconf_client_set_string()</entry><entry>g_settings_set_string()</entry></row>
|
|
<row><entry>gconf_client_get_list()</entry><entry>for string lists, see g_settings_get_strv(), else see g_settings_get_value() and #GVariant API</entry></row>
|
|
<row><entry>gconf_client_set_list()</entry><entry>for string lists, see g_settings_set_strv(), else see g_settings_set_value() and #GVariant API</entry></row>
|
|
<row><entry>gconf_entry_get_is_writable()</entry><entry>g_settings_is_writable()</entry></row>
|
|
<row><entry>gconf_client_notify_add()</entry><entry>not required, the #GSettings::changed signal is emitted automatically</entry></row>
|
|
<row><entry>gconf_client_add_dir()</entry><entry>not required, each GSettings instance automatically watches all keys in its path</entry></row>
|
|
<row><entry>#GConfChangeSet</entry><entry>g_settings_delay(), g_settings_apply()</entry></row>
|
|
<row><entry>gconf_client_get_default_from_schema()</entry><entry>no equivalent, applications are expected to know their schema</entry></row>
|
|
<row><entry>gconf_client_all_entries()</entry><entry>no equivalent, applications are expected to know their schema, and GSettings does not allow schema-less entries</entry></row>
|
|
<row><entry>gconf_client_get_without_default()</entry><entry>no equivalent</entry></row>
|
|
<row><entry>gconf_bridge_bind_property()</entry><entry>g_settings_bind()</entry></row>
|
|
<row><entry>gconf_bridge_bind_property_full()</entry><entry>g_settings_bind_with_mapping()</entry></row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</para>
|
|
<para>
|
|
GConfBridge was a third-party library that used GConf to bind an object property
|
|
to a particular configuration key. GSettings offers this service itself.
|
|
</para>
|
|
<para>
|
|
There is a pattern that is sometimes used for GConf, where a setting can have
|
|
explicit 'value A', explicit 'value B' or 'use the system default'. With GConf,
|
|
'use the system default' is sometimes implemented by unsetting the user value.
|
|
</para>
|
|
<para>
|
|
This is not possible in GSettings, since it does not have API to determine if a value
|
|
is the default and does not let you unset values. The recommended way (and much
|
|
clearer) way in which this can be implemented in GSettings is to have a separate
|
|
'use-system-default' boolean setting.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Change notification</title>
|
|
|
|
<para>
|
|
GConf requires you to call gconf_client_add_dir() and
|
|
gconf_client_notify_add() to get change notification. With
|
|
GSettings, this is not necessary; signals get emitted automatically
|
|
for every change.
|
|
</para>
|
|
<para>
|
|
The #GSettings::changed signal is emitted for each changed key.
|
|
There is also a #GSettings::change-event signal that you can handle
|
|
if you need to see groups of keys that get changed at the same time.
|
|
</para>
|
|
<para>
|
|
GSettings also notifies you about changes in writability of keys,
|
|
with the #GSettings::writable-changed signal (and the
|
|
#GSettings::writable-change-event signal).
|
|
</para>
|
|
</section>
|
|
|
|
<section><title>Change sets</title>
|
|
<para>
|
|
GConf has a a concept of a set of changes which can be applied or reverted
|
|
at once: #GConfChangeSet (GConf doesn't actually apply changes atomically,
|
|
which is one of its shortcomings).
|
|
</para>
|
|
<para>
|
|
Instead of a separate object to represent a change set, GSettings has a
|
|
'delayed-apply' mode, which can be turned on for a GSettings object by
|
|
calling g_settings_delay(). In this mode, changes done to the GSettings
|
|
object are not applied - they are still visible when calling g_settings_get()
|
|
<emphasis>on the same object</emphasis>, but not to other GSettings instances
|
|
or even other processes.
|
|
</para>
|
|
<para>
|
|
To apply the pending changes all at once (GSettings <emphasis>does</emphasis>
|
|
atomicity here), call g_settings_apply(). To revert the pending changes,
|
|
call g_settings_revert() or just drop the reference to the #GSettings object.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Schema conversion</title>
|
|
|
|
<para>
|
|
If you are porting your application from GConf, most likely you already
|
|
have a GConf schema. GConf comes with a commandline tool
|
|
gsettings-schema-convert that can help with the task of converting
|
|
a GConf schema into an equivalent GSettings schema. The tool is not
|
|
perfect and may need assistence in some cases.
|
|
</para>
|
|
<example><title>An example for using gsettings-schema-convert</title>
|
|
<para>Running <userinput>gsettings-schema-convert --gconf --xml --schema-id "org.gnome.font-rendering" --output org.gnome.font-rendering.gschema.xml destop_gnome_font_rendering.schemas</userinput> on the following <filename>desktop_gnome_font_rendering.schemas</filename> file:
|
|
<programlisting>
|
|
<![CDATA[
|
|
<?xml version="1.0"?>
|
|
<gconfschemafile>
|
|
<schemalist>
|
|
<schema>
|
|
<key>/schemas/desktop/gnome/font_rendering/dpi</key>
|
|
<applyto>/desktop/gnome/font_rendering/dpi</applyto>
|
|
<owner>gnome</owner>
|
|
<type>int</type>
|
|
<default>96</default>
|
|
<locale name="C">
|
|
<short>DPI</short>
|
|
<long>The resolution used for converting font sizes to pixel sizes, in dots per inch.</long>
|
|
</locale>
|
|
</schema>
|
|
</schemalist>
|
|
</gconfschemafile>
|
|
]]>
|
|
</programlisting>
|
|
produces a <filename>org.gnome.font-rendering.gschema.xml</filename> file with the following content:
|
|
<programlisting>
|
|
<![CDATA[
|
|
<schemalist>
|
|
<schema id="org.gnome.font-rendering" path="/desktop/gnome/font_rendering/">
|
|
<key name="dpi" type="i">
|
|
<default>96</default>
|
|
<summary>DPI</summary>
|
|
<description>The resolution used for converting font sizes to pixel sizes, in dots per inch.</description>
|
|
</key>
|
|
</schema>
|
|
</schemalist>
|
|
]]>
|
|
</programlisting>
|
|
</para>
|
|
</example>
|
|
|
|
<para>
|
|
GSettings schemas are identified at runtime by their id (as specified
|
|
in the XML source file). It is recommended to use a dotted name as schema
|
|
id, similar in style to a D-Bus bus name, e.g. "org.gnome.SessionManager".
|
|
In cases where the settings are general and not specific to one application,
|
|
the id should not use StudlyCaps, e.g. "org.gnome.font-rendering".
|
|
The filename used for the XML schema source is immaterial, but
|
|
schema compiler expects the files to have the extension
|
|
<filename>.gschema.xml</filename>. It is recommended to simply
|
|
use the schema id as the filename, followed by this extension,
|
|
e.g. <filename>org.gnome.SessionManager.gschema.xml</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
The XML source file for your GSettings schema needs to get installed
|
|
into <filename>$datadir/glib-2.0/schemas</filename>, and needs to be
|
|
compiled into a binary form. At runtime, GSettings looks for compiled
|
|
schemas in the <filename>glib-2.0/schemas</filename> subdirectories
|
|
of all <envar>XDG_DATA_DIRS</envar> directories, so if you install
|
|
your schema in a different location, you need to set the
|
|
<envar>XDG_DATA_DIRS</envar> environment variable appropriately.
|
|
</para>
|
|
<para>
|
|
Schemas are compiled into binary form by the
|
|
<link linkend="glib-compile-schemas">glib-compile-schemas</link> utility.
|
|
GIO provides a <literal>glib_compile_schemas</literal>
|
|
variable for the schema compiler.
|
|
</para>
|
|
<para>
|
|
You can ignore all of this by using the provided m4 macros. To
|
|
do this, add to your <filename>configure.ac</filename>:
|
|
<programlisting>
|
|
GLIB_GSETTINGS
|
|
</programlisting>
|
|
The corresponding <filename>Makefile.am</filename> fragment looks like
|
|
this:
|
|
<programlisting>
|
|
# gsettings_SCHEMAS is a list of all the schemas you want to install
|
|
gsettings_SCHEMAS = my.app.gschema.xml
|
|
|
|
# include the appropriate makefile rules for schema handling
|
|
@GSETTINGS_RULES@
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
This is not sufficient on its own. You need to mention what the source
|
|
of the <filename>my.app.gschema.xml</filename> file is. If the schema
|
|
file is distributed directly with your project's tarball then a mention
|
|
in <varname>EXTRA_DIST</varname> is appropriate. If the schema file is
|
|
generated from another source then you will need the appropriate rule
|
|
for that, plus probably an item in <varname>EXTRA_DIST</varname> for the
|
|
source files used by that rule.
|
|
</para>
|
|
|
|
<para>
|
|
One possible pitfall in doing schema conversion is that the default
|
|
values in GSettings schemas are parsed by the #GVariant parser.
|
|
This means that strings need to include quotes in the XML. Also note
|
|
that the types are now specified as #GVariant type strings.
|
|
<programlisting>
|
|
<![CDATA[
|
|
<type>string</type>
|
|
<default>rgb</default>
|
|
]]>
|
|
</programlisting>
|
|
becomes
|
|
<programlisting>
|
|
<![CDATA[
|
|
<key name="rgba-order" type="s">
|
|
<default>'rgb'</default> <!-- note quotes -->
|
|
</key>
|
|
]]>
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Another possible complication is that GConf specifies full paths
|
|
for each key, while a GSettings schema has a 'path' attribute that
|
|
contains the prefix for all the keys in the schema, and individual
|
|
keys just have a simple name. So
|
|
<programlisting>
|
|
<![CDATA[
|
|
<key>/schemas/desktop/gnome/font_rendering/antialiasing</key>
|
|
]]>
|
|
</programlisting>
|
|
becomes
|
|
<programlisting>
|
|
<![CDATA[
|
|
<schema id="org.gnome.font" path="/desktop/gnome/font_rendering/">
|
|
<key name="antialiasing" type="s">
|
|
]]>
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Default values can be localized in both GConf and GSettings schemas,
|
|
but GSettings uses gettext for the localization. You can specify
|
|
the gettext domain to use in the <tag class="attribute">gettext-domain</tag>
|
|
attribute. Therefore, when converting localized defaults in GConf,
|
|
<programlisting>
|
|
<![CDATA[
|
|
<key>/schemas/apps/my_app/font_size</key>
|
|
<locale name="C">
|
|
<default>18</default>
|
|
</locale>
|
|
<locale name="be">
|
|
<default>24</default>
|
|
</locale>
|
|
</key>
|
|
]]>
|
|
</programlisting>
|
|
becomes
|
|
<programlisting>
|
|
<![CDATA[
|
|
<schema id="..." gettext-domain="your-domain">
|
|
...
|
|
<key name="font-size" type="i">
|
|
<default l10n="messages" context="font_size">18</default>
|
|
</key>
|
|
]]>
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
GSettings uses gettext for translation of default values.
|
|
The string that is translated is exactly the string that appears
|
|
inside of the <tag class='starttag'>default</tag> element. This
|
|
includes the quotation marks that appear around strings.
|
|
Default values must be marked with the <varname>l10n</varname>
|
|
attribute in the <tag class='starttag'>default</tag> tag, which
|
|
should be set as equal to <literal>'messages'</literal> or
|
|
<literal>'time'</literal> depending on the desired category. An
|
|
optional translation context can also be specified with the
|
|
<varname>context</varname> attribute, as in the example. This
|
|
is usually recommended, since the string "<literal>18</literal>"
|
|
is not particularly easy to translate without context. The
|
|
translated version of the default value should be stored in the
|
|
specified <varname>gettext-domain</varname>. Care must be taken
|
|
during translation to ensure that all translated values remain
|
|
syntactically valid; mistakes here will cause runtime errors.
|
|
</para>
|
|
<para>
|
|
GSettings schemas have optional <tag class="starttag">summary</tag> and
|
|
<tag class="starttag">description</tag> elements for each key which
|
|
correspond to the <tag class="starttag">short</tag> and
|
|
<tag class="starttag">long</tag> elements in the GConf schema and
|
|
will be used in similar ways by a future gsettings-editor, so you
|
|
should use the same conventions for them: The summary is just a short
|
|
label with no punctuation, the description can be one or more complete
|
|
sentences. If multiple paragraphs are desired for the description, the
|
|
paragraphs should be separated by a completely empty line.
|
|
</para>
|
|
<para>
|
|
Translations for these strings will also be handled
|
|
via gettext, so you should arrange for these strings to be
|
|
extracted into your gettext catalog. One way to do that is to use
|
|
intltool. Since intltool 0.50.1, schema files are
|
|
supported, so all you have to do is to add your .gschema.xml
|
|
files to <filename>POTFILES.in</filename> with a line like
|
|
<programlisting>
|
|
[type: gettext/gsettings]data/org.foo.MyApp.gschema.xml
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
GSettings is a bit more restrictive about key names than GConf. Key
|
|
names in GSettings can be at most 32 characters long, and must only
|
|
consist of lowercase characters, numbers and dashes, with no
|
|
consecutive dashes. The first character must not be a number or dash,
|
|
and the last character cannot be '-'.
|
|
</para>
|
|
<para>
|
|
If you are using the GConf backend for GSettings during the
|
|
transition, you may want to keep your key names the same they
|
|
were in GConf, so that existing settings in the users GConf
|
|
database are preserved. You can achieve this by using the
|
|
<option>--allow-any-name</option> with the
|
|
<link linkend="glib-compile-schemas">glib-compile-schemas</link> schema
|
|
compiler. Note that this option is only meant
|
|
to ease the process of porting your application, allowing parts
|
|
of your application to continue to access GConf and parts to use
|
|
GSettings. By the time you have finished porting your application
|
|
you must ensure that all key names are valid.
|
|
</para>
|
|
</section>
|
|
|
|
<section><title>Data conversion</title>
|
|
<para>
|
|
GConf comes with a GSettings backend that can be used to
|
|
facility the transition to the GSettings API until you are
|
|
ready to make the jump to a different backend (most likely
|
|
dconf). To use it, you need to set the <envar>GSETTINGS_BACKEND</envar>
|
|
to 'gconf', e.g. by using
|
|
<programlisting>
|
|
g_setenv ("GSETTINGS_BACKEND", "gconf", TRUE);
|
|
</programlisting>
|
|
early on in your program. Note that this backend is meant purely
|
|
as a transition tool, and should not be used in production.
|
|
</para>
|
|
<para>
|
|
GConf also comes with a utility called
|
|
<command>gsettings-data-convert</command>, which is designed to help
|
|
with the task of migrating user settings from GConf into another
|
|
GSettings backend. It can be run manually, but it is designed to be
|
|
executed automatically, every time a user logs in. It keeps track of
|
|
the data migrations that it has already done, and it is harmless to
|
|
run it more than once.
|
|
</para>
|
|
<para>
|
|
To make use of this utility, you must install a keyfile in the
|
|
directory <filename>/usr/share/GConf/gsettings</filename> which
|
|
lists the GSettings keys and GConf paths to map to each other, for
|
|
each schema that you want to migrate user data for.
|
|
</para>
|
|
<para>
|
|
Here is an example:
|
|
<programlisting>
|
|
<![CDATA[
|
|
[org.gnome.fonts]
|
|
antialiasing = /desktop/gnome/font_rendering/antialiasing
|
|
dpi = /desktop/gnome/font_rendering/dpi
|
|
hinting = /desktop/gnome/font_rendering/hinting
|
|
rgba-order = /desktop/gnome/font_rendering/rgba_order
|
|
|
|
[apps.myapp:/path/to/myapps/]
|
|
some-odd-key1 = /apps/myapp/some_ODD-key1
|
|
]]>
|
|
</programlisting>
|
|
The last key demonstrates that it may be necessary to modify the key
|
|
name to comply with stricter GSettings key name rules. Of course,
|
|
that means your application must use the new key names when looking
|
|
up settings in GSettings.
|
|
</para>
|
|
<para>
|
|
The last group in the example also shows how to handle the case
|
|
of 'relocatable' schemas, which don't have a fixed path. You can
|
|
specify the path to use in the group name, separated by a colon.
|
|
</para>
|
|
<para>
|
|
There are some limitations: <command>gsettings-data-convert</command>
|
|
does not do any transformation of the values. And it does not handle
|
|
complex GConf types other than lists of strings or integers.
|
|
</para>
|
|
<para>
|
|
Don't forget to require GConf 2.31.1 or newer in your configure
|
|
script if you are making use of the GConf backend or the conversion
|
|
utility.
|
|
</para>
|
|
|
|
<para>
|
|
If, as an application developer, you are interested in manually
|
|
ensuring that <command>gsettings-data-convert</command> has been
|
|
invoked (for example, to deal with the case where the user is
|
|
logged in during a distribution upgrade or for non-XDG desktop
|
|
environments which do not run the command as an autostart) you
|
|
may invoke it manually during your program initialisation. This
|
|
is not recommended for all application authors -- it is your
|
|
choice if this use case concerns you enough.
|
|
</para>
|
|
<para>
|
|
Internally, <command>gsettings-data-convert</command> uses a
|
|
keyfile to track which settings have been migrated. The
|
|
following code fragment will check that keyfile to see if your
|
|
data conversion script has been run yet and, if not, will
|
|
attempt to invoke the tool to run it. You should adapt it to
|
|
your application as you see fit.
|
|
</para>
|
|
<para>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void
|
|
ensure_migrated (const gchar *name)
|
|
{
|
|
gboolean needed = TRUE;
|
|
GKeyFile *kf;
|
|
gchar **list;
|
|
gsize i, n;
|
|
|
|
kf = g_key_file_new ();
|
|
|
|
g_key_file_load_from_data_dirs (kf, "gsettings-data-convert",
|
|
NULL, G_KEY_FILE_NONE, NULL);
|
|
list = g_key_file_get_string_list (kf, "State", "converted", &n, NULL);
|
|
|
|
if (list)
|
|
{
|
|
for (i = 0; i < n; i++)
|
|
if (strcmp (list[i], name) == 0)
|
|
{
|
|
needed = FALSE;
|
|
break;
|
|
}
|
|
|
|
g_strfreev (list);
|
|
}
|
|
|
|
g_key_file_free (kf);
|
|
|
|
if (needed)
|
|
g_spawn_command_line_sync ("gsettings-data-convert",
|
|
NULL, NULL, NULL, NULL);
|
|
}
|
|
|
|
]]>
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Although there is the possibility that the
|
|
<command>gsettings-data-convert</command> script will end up
|
|
running multiple times concurrently with this approach, it is
|
|
believed that this is safe.
|
|
</para>
|
|
</section>
|
|
</chapter>
|