The Glib.Settings_Schema_Source.Gsettings_Schema_Source and Glib.Settings_Schema.Gsettings_Schema APIs provide a mechanism for advanced control over the loading of schemas and a mechanism for introspecting their content.
Plugin loading systems that wish to provide plugins a way to access settings face the problem of how to make the schemas for these settings visible to GSettings. Typically, a plugin will want to ship the schema along with itself and it won't be installed into the standard system directories for schemas.
Glib.Settings_Schema_Source.Gsettings_Schema_Source provides a mechanism for dealing with this by allowing the creation of a new 'schema source' from which schemas can be acquired. This schema source can then become part of the metadata associated with the plugin and queried whenever the plugin requires access to some settings.
Consider the following example:
typedef struct
{
...
GSettingsSchemaSource *schema_source;
...
} Plugin;
Plugin *
initialise_plugin (const gchar *dir)
{
Plugin *plugin;
...
plugin->schema_source =
g_settings_schema_source_new_from_directory (dir,
g_settings_schema_source_get_default (), FALSE, NULL);
...
return plugin;
}
...
GSettings *
plugin_get_settings (Plugin *plugin,
const gchar *schema_id)
{
GSettingsSchema *schema;
if (schema_id == NULL)
schema_id = plugin->identifier;
schema = g_settings_schema_source_lookup (plugin->schema_source,
schema_id, FALSE);
if (schema == NULL)
{
... disable the plugin or abort, etc ...
}
return g_settings_new_full (schema, NULL, NULL);
}
The code above shows how hooks should be added to the code that initialises (or enables) the plugin to create the schema source and how an API can be added to the plugin system to provide a convenient way for the plugin to access its settings, using the schemas that it ships.
From the standpoint of the plugin, it would need to ensure that it ships a gschemas.compiled file as part of itself, and then simply do the following:
{
GSettings *settings;
gint some_value;
settings = plugin_get_settings (self, NULL);
some_value = g_settings_get_int (settings, "some-value");
...
}
It's also possible that the plugin system expects the schema source files (ie: .gschema.xml files) instead of a gschemas.compiled file. In that case, the plugin loading system must compile the schemas for itself before attempting to create the settings source.
<group>GIO</group> <gtkada_demo>create_settings.adb</gtkada_demo>
function From_Object (Object : System.Address) return Gsettings_Schema
function From_Object_Free (B : access Gsettings_Schema'Class) return Gsettings_Schema
function Get_Id (Self : Gsettings_Schema) return UTF8_String
Get the ID of Schema.
the ID
function Get_Key
(Self : Gsettings_Schema;
Name : UTF8_String)
return Glib.Settings_Schema_Key.Gsettings_Schema_Key
Gets the key named Name from Schema. It is a programmer error to request a key that does not exist. See Glib.Settings_Schema.List_Keys. Since: gtk+ 2.40
the name of a key
the Glib.Settings_Schema_Key.Gsettings_Schema_Key for Name. Has transfer-ownership='full'.
function Get_Path (Self : Gsettings_Schema) return UTF8_String
Gets the path associated with Schema, or null. Schemas may be single-instance or relocatable. Single-instance schemas correspond to exactly one set of keys in the backend database: those located at the path returned by this function. Relocatable schemas can be referenced by other schemas and can therefore describe multiple sets of keys at different locations. For relocatable schemas, this function will return null. Since: gtk+ 2.32
the path of the schema, or null
function Get_Type return Glib.GType
type Gsettings_Schema is new Glib.C_Boxed with null record;
function Has_Key
(Self : Gsettings_Schema;
Name : UTF8_String) return Boolean
Checks if Schema has a key named Name. Since: gtk+ 2.40
the name of a key
True if such a key exists
function List_Children
(Self : Gsettings_Schema) return GNAT.Strings.String_List
Gets the list of children in Schema. You should free the return value with g_strfreev when you are done with it. Since: gtk+ 2.44
a list of the children on Settings, in no defined order
function List_Keys
(Self : Gsettings_Schema) return GNAT.Strings.String_List
Introspects the list of keys on Schema. You should probably not be calling this function from "normal" code (since you should already know what keys are in your schema). This function is intended for introspection reasons. Since: gtk+ 2.46
a list of the keys on Schema, in no defined order
Null_Gsettings_Schema : constant Gsettings_Schema;
function Ref (Self : Gsettings_Schema) return Gsettings_Schema
Increase the reference count of Schema, returning a new reference. Since: gtk+ 2.32
a new reference to Schema. Has transfer-ownership='full'.
procedure Unref (Self : Gsettings_Schema)
Decrease the reference count of Schema, possibly freeing it. Since: gtk+ 2.32