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Add an optional PropertiesChanged() signal

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Some notes about this new signal

 - The PropertiesChanged() signal is optional. An application can
   convey support for this signal by either including or excluding it
   from the returned introspection data much like apps not supporting
   (or predating) the GetAll() method does not include GetAll() in the
   introspection data.

 - An object can use PropertiesChanged() but opt out of using it for
   one or more properties by using the

     org.freedesktop.DBus.Properties.EmitsChangedSignal

   annotation on the properties in question

 - Applications can start using this new signal without breaking
   compatibility with clients relying on existing D-Bus API.

The intent of the patch is simply to standardize existing behavior

 - EggDBus has a very similar signal called EggDBusPropertiesChanged()
   (also on the org.freedesktop.DBus.Properties interface)

 - NetworkManager has a PropertiesChanged() signal on each different
   interface (e.g. not org.fd.D.P) that it implements

 - GDBus, an implementation of the D-Bus protocol in GLib, already
   implements this signal

Signed-off-by: David Zeuthen <davidz@redhat.com>
This commit is contained in:
David Zeuthen 2010-05-07 12:50:47 -04:00
parent 1af558a620
commit 2541e86615
1 changed files with 32 additions and 2 deletions
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34
doc/dbus-specification.xml
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@ -7,8 +7,8 @@
<article id="index">
<articleinfo>
<title>D-Bus Specification</title>
<releaseinfo>Version 0.13</releaseinfo>
<date>23 Dezember 2009</date>
<releaseinfo>Version 0.14</releaseinfo>
<date>May 12, 2010</date>
<authorgroup>
<author>
<firstname>Havoc</firstname>
@ -2757,6 +2757,31 @@
deterministic rule, or returning an error, are the reasonable
possibilities).
</para>
<para>
If one or more properties change on an object, the
<literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
signal may be emitted (this signal was added in 0.14):
</para>
<para>
<programlisting>
org.freedesktop.DBus.Properties.PropertiesChanged (STRING interface_name,
DICT&lt;STRING,VARIANT&gt; changed_properties);
</programlisting>
</para>
<para>
where <literal>changed_properties</literal> is a dictionary
containing the changed properties and the new values.
</para>
<para>
Whether the <literal>PropertiesChanged</literal> signal is
supported can be determined by calling
<literal>org.freedesktop.DBus.Introspectable.Introspect</literal>. If
the signal is supported for an object but not used for one or
more properties (for e.g. performance reasons), each such
property must be annotated with the
<literal>org.freedesktop.DBus.Properties.EmitsChangedSignal</literal>
annotation.
</para>
</sect2>
</sect1>
@ -2887,6 +2912,11 @@
<entry>true,false</entry>
<entry>If set, don't expect a reply to the method call; defaults to false.</entry>
</row>
<row>
<entry>org.freedesktop.DBus.Properties.EmitsChangedSignal</entry>
<entry>true,true_no_value,false</entry>
<entry>If set to false, the <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal> signal, see <xref linkend="standard-interfaces-properties"/>, is not emitted if the property changes. If set to true_no_value the signal is emitted but the value is no included in the signal. Defaults to true.</entry>
</row>
</tbody>
</tgroup>
</informaltable>