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| author | Leo Tenenbaum <pommicket@gmail.com> | 2018-08-20 21:12:06 -0400 |
|---|---|---|
| committer | Leo Tenenbaum <pommicket@gmail.com> | 2018-08-20 21:12:06 -0400 |
| commit | 63e87c2d0c9d263f14c77b68f85c67d46ece82a9 (patch) | |
| tree | 6260365cbf7d24f37d27669e8538227fcb72e243 /gtk+-mingw/share/gtk-doc/html/gobject/gobject-properties.html | |
| parent | a4460f6d9453bbd7e584937686449cef3e19f052 (diff) | |
Diffstat (limited to 'gtk+-mingw/share/gtk-doc/html/gobject/gobject-properties.html')
| -rw-r--r-- | gtk+-mingw/share/gtk-doc/html/gobject/gobject-properties.html | 272 |
1 files changed, 0 insertions, 272 deletions
diff --git a/gtk+-mingw/share/gtk-doc/html/gobject/gobject-properties.html b/gtk+-mingw/share/gtk-doc/html/gobject/gobject-properties.html deleted file mode 100644 index f4c2b0e..0000000 --- a/gtk+-mingw/share/gtk-doc/html/gobject/gobject-properties.html +++ /dev/null @@ -1,272 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> -<html> -<head> -<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> -<title>Object properties</title> -<meta name="generator" content="DocBook XSL Stylesheets V1.76.1"> -<link rel="home" href="index.html" title="GObject Reference Manual"> -<link rel="up" href="chapter-gobject.html" title="The GObject base class"> -<link rel="prev" href="gobject-memory.html" title="Object memory management"> -<link rel="next" href="chapter-signal.html" title="The GObject messaging system"> -<meta name="generator" content="GTK-Doc V1.18 (XML mode)"> -<link rel="stylesheet" href="style.css" type="text/css"> -</head> -<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> -<table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="2"><tr valign="middle"> -<td><a accesskey="p" href="gobject-memory.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td> -<td><a accesskey="u" href="chapter-gobject.html"><img src="up.png" width="24" height="24" border="0" alt="Up"></a></td> -<td><a accesskey="h" href="index.html"><img src="home.png" width="24" height="24" border="0" alt="Home"></a></td> -<th width="100%" align="center">GObject Reference Manual</th> -<td><a accesskey="n" href="chapter-signal.html"><img src="right.png" width="24" height="24" border="0" alt="Next"></a></td> -</tr></table> -<div class="sect1"> -<div class="titlepage"><div><div><h2 class="title" style="clear: both"> -<a name="gobject-properties"></a>Object properties</h2></div></div></div> -<p> - One of GObject's nice features is its generic get/set mechanism for object - properties. When an object - is instantiated, the object's class_init handler should be used to register - the object's properties with <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-class-install-properties" title="g_object_class_install_properties ()">g_object_class_install_properties</a></code> - (implemented in <code class="filename">gobject.c</code>). - </p> -<p> - The best way to understand how object properties work is by looking at a real example - on how it is used: -</p> -<div class="informalexample"><pre class="programlisting"> -/************************************************/ -/* Implementation */ -/************************************************/ - -enum -{ - PROP_0, - - PROP_MAMAN_NAME, - PROP_PAPA_NUMBER, - - N_PROPERTIES -}; - -static GParamSpec *obj_properties[N_PROPERTIES] = { NULL, }; - -static void -maman_bar_set_property (GObject *object, - guint property_id, - const GValue *value, - GParamSpec *pspec) -{ - MamanBar *self = MAMAN_BAR (object); - - switch (property_id) - { - case PROP_MAMAN_NAME: - g_free (self->priv->name); - self->priv->name = g_value_dup_string (value); - g_print ("maman: %s\n", self->priv->name); - break; - - case PROP_PAPA_NUMBER: - self->priv->papa_number = g_value_get_uchar (value); - g_print ("papa: %u\n", self->priv->papa_number); - break; - - default: - /* We don't have any other property... */ - G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec); - break; - } -} - -static void -maman_bar_get_property (GObject *object, - guint property_id, - GValue *value, - GParamSpec *pspec) -{ - MamanBar *self = MAMAN_BAR (object); - - switch (property_id) - { - case PROP_MAMAN_NAME: - g_value_set_string (value, self->priv->name); - break; - - case PROP_PAPA_NUMBER: - g_value_set_uchar (value, self->priv->papa_number); - break; - - default: - /* We don't have any other property... */ - G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec); - break; - } -} - -static void -maman_bar_class_init (MamanBarClass *klass) -{ - GObjectClass *gobject_class = G_OBJECT_CLASS (klass); - - gobject_class->set_property = maman_bar_set_property; - gobject_class->get_property = maman_bar_get_property; - - obj_properties[PROP_NAME] = - g_param_spec_string ("maman-name", - "Maman construct prop", - "Set maman's name", - "no-name-set" /* default value */, - G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE); - - obj_properties[PROP_NUMBER] = - g_param_spec_uchar ("papa-number", - "Number of current Papa", - "Set/Get papa's number", - 0 /* minimum value */, - 10 /* maximum value */, - 2 /* default value */, - G_PARAM_READWRITE); - - g_object_class_install_properties (gobject_class, - N_PROPERTIES, - obj_properties); -} - -/************************************************/ -/* Use */ -/************************************************/ - -GObject *bar; -GValue val = G_VALUE_INIT; - -bar = g_object_new (MAMAN_TYPE_SUBBAR, NULL); - -g_value_init (&val, G_TYPE_CHAR); -g_value_set_char (&val, 11); - -g_object_set_property (G_OBJECT (bar), "papa-number", &val); - -g_value_unset (&val); -</pre></div> -<p> - The client code just above looks simple but a lot of things happen under the hood: - </p> -<p> - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set-property" title="g_object_set_property ()">g_object_set_property</a></code> first ensures a property - with this name was registered in bar's class_init handler. If so it walks the class hierarchy, - from bottom, most derived type, to top, fundamental type to find the class - which registered that property. It then tries to convert the user-provided GValue - into a GValue whose type is that of the associated property. - </p> -<p> - If the user provides a signed char GValue, as is shown - here, and if the object's property was registered as an unsigned int, - <code class="function"><a class="link" href="gobject-Generic-values.html#g-value-transform" title="g_value_transform ()">g_value_transform</a></code> will try to transform the input signed char into - an unsigned int. Of course, the success of the transformation depends on the availability - of the required transform function. In practice, there will almost always be a transformation - <sup>[<a name="idp10972864" href="#ftn.idp10972864" class="footnote">4</a>]</sup> - which matches and conversion will be carried out if needed. - </p> -<p> - After transformation, the <a class="link" href="gobject-Generic-values.html#GValue" title="GValue"><span class="type">GValue</span></a> is validated by - <code class="function"><a class="link" href="gobject-GParamSpec.html#g-param-value-validate" title="g_param_value_validate ()">g_param_value_validate</a></code> which makes sure the user's - data stored in the <a class="link" href="gobject-Generic-values.html#GValue" title="GValue"><span class="type">GValue</span></a> matches the characteristics specified by - the property's <a class="link" href="gobject-GParamSpec.html#GParamSpec" title="struct GParamSpec"><span class="type">GParamSpec</span></a>. - Here, the <a class="link" href="gobject-GParamSpec.html#GParamSpec" title="struct GParamSpec"><span class="type">GParamSpec</span></a> we - provided in class_init has a validation function which makes sure that the GValue - contains a value which respects the minimum and maximum bounds of the - <a class="link" href="gobject-GParamSpec.html#GParamSpec" title="struct GParamSpec"><span class="type">GParamSpec</span></a>. In the example above, the client's GValue does not - respect these constraints (it is set to 11, while the maximum is 10). As such, the - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set-property" title="g_object_set_property ()">g_object_set_property</a></code> function will return with an error. - </p> -<p> - If the user's GValue had been set to a valid value, <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set-property" title="g_object_set_property ()">g_object_set_property</a></code> - would have proceeded with calling the object's set_property class method. Here, since our - implementation of Foo did override this method, the code path would jump to - <code class="function">foo_set_property</code> after having retrieved from the - <a class="link" href="gobject-GParamSpec.html#GParamSpec" title="struct GParamSpec"><span class="type">GParamSpec</span></a> the <span class="emphasis"><em>param_id</em></span> - <sup>[<a name="idp10984640" href="#ftn.idp10984640" class="footnote">5</a>]</sup> - which had been stored by - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-class-install-property" title="g_object_class_install_property ()">g_object_class_install_property</a></code>. - </p> -<p> - Once the property has been set by the object's set_property class method, the code path - returns to <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set-property" title="g_object_set_property ()">g_object_set_property</a></code> which makes sure that - the "notify" signal is emitted on the object's instance with the changed property as - parameter unless notifications were frozen by <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-freeze-notify" title="g_object_freeze_notify ()">g_object_freeze_notify</a></code>. - </p> -<p> - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-thaw-notify" title="g_object_thaw_notify ()">g_object_thaw_notify</a></code> can be used to re-enable notification of - property modifications through the "notify" signal. It is important to remember that - even if properties are changed while property change notification is frozen, the "notify" - signal will be emitted once for each of these changed properties as soon as the property - change notification is thawed: no property change is lost for the "notify" signal. Signal - can only be delayed by the notification freezing mechanism. - </p> -<p> - It sounds like a tedious task to set up GValues every time when one wants to modify a property. - In practice one will rarely do this. The functions <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set-property" title="g_object_set_property ()">g_object_set_property</a></code> - and <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-get-property" title="g_object_get_property ()">g_object_get_property</a></code> - are meant to be used by language bindings. For application there is an easier way and - that is described next. - </p> -<div class="sect2"> -<div class="titlepage"><div><div><h3 class="title"> -<a name="gobject-multi-properties"></a>Accessing multiple properties at once</h3></div></div></div> -<p> - It is interesting to note that the <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set" title="g_object_set ()">g_object_set</a></code> and - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set-valist" title="g_object_set_valist ()">g_object_set_valist</a></code> (vararg version) functions can be used to set - multiple properties at once. The client code shown above can then be re-written as: -</p> -<pre class="programlisting"> -MamanBar *foo; -foo = /* */; -g_object_set (G_OBJECT (foo), - "papa-number", 2, - "maman-name", "test", - NULL); -</pre> -<p> - This saves us from managing the GValues that we were needing to handle when using - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set-property" title="g_object_set_property ()">g_object_set_property</a></code>. - The code above will trigger one notify signal emission for each property modified. - </p> -<p> - Of course, the _get versions are also available: <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-get" title="g_object_get ()">g_object_get</a></code> - and <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-get-valist" title="g_object_get_valist ()">g_object_get_valist</a></code> (vararg version) can be used to get numerous - properties at once. - </p> -<p> - These high level functions have one drawback - they don't provide a return result. - One should pay attention to the argument types and ranges when using them. - A known source of errors is to e.g. pass a gfloat instead of a gdouble and thus - shifting all subsequent parameters by four bytes. Also forgetting the terminating - NULL will lead to unexpected behaviour. - </p> -<p> - Really attentive readers now understand how <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-new" title="g_object_new ()">g_object_new</a></code>, - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-newv" title="g_object_newv ()">g_object_newv</a></code> and <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-new-valist" title="g_object_new_valist ()">g_object_new_valist</a></code> - work: they parse the user-provided variable number of parameters and invoke - <code class="function"><a class="link" href="gobject-The-Base-Object-Type.html#g-object-set" title="g_object_set ()">g_object_set</a></code> on the parameters only after the object has been successfully constructed. - Of course, the "notify" signal will be emitted for each property set. - </p> -</div> -<div class="footnotes"> -<br><hr width="100" align="left"> -<div class="footnote"><p><sup>[<a id="ftn.idp10972864" href="#idp10972864" class="para">4</a>] </sup>Its behaviour might not be what you expect but it is up to you to actually avoid - relying on these transformations. - </p></div> -<div class="footnote"><p><sup>[<a id="ftn.idp10984640" href="#idp10984640" class="para">5</a>] </sup> - It should be noted that the param_id used here need only to uniquely identify each - <a class="link" href="gobject-GParamSpec.html#GParamSpec" title="struct GParamSpec"><span class="type">GParamSpec</span></a> within the <span class="type">FooClass</span> such that the switch - used in the set and get methods actually works. Of course, this locally-unique - integer is purely an optimization: it would have been possible to use a set of - <span class="emphasis"><em>if (strcmp (a, b) == 0) {} else if (strcmp (a, b) == 0) {}</em></span> statements. - </p></div> -</div> -</div> -<div class="footer"> -<hr> - Generated by GTK-Doc V1.18</div> -</body> -</html>
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