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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/howto-gobject-chainup.html | |
| parent | a4460f6d9453bbd7e584937686449cef3e19f052 (diff) | |
Diffstat (limited to 'gtk+-mingw/share/gtk-doc/html/gobject/howto-gobject-chainup.html')
| -rw-r--r-- | gtk+-mingw/share/gtk-doc/html/gobject/howto-gobject-chainup.html | 100 |
1 files changed, 0 insertions, 100 deletions
diff --git a/gtk+-mingw/share/gtk-doc/html/gobject/howto-gobject-chainup.html b/gtk+-mingw/share/gtk-doc/html/gobject/howto-gobject-chainup.html deleted file mode 100644 index 8118c27..0000000 --- a/gtk+-mingw/share/gtk-doc/html/gobject/howto-gobject-chainup.html +++ /dev/null @@ -1,100 +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>Chaining up</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="howto-gobject.html" title="How to define and implement a new GObject"> -<link rel="prev" href="howto-gobject-methods.html" title="Object methods"> -<link rel="next" href="howto-interface.html" title="How to define and implement interfaces"> -<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="howto-gobject-methods.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td> -<td><a accesskey="u" href="howto-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="howto-interface.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="howto-gobject-chainup"></a>Chaining up</h2></div></div></div> -<p>Chaining up is often loosely defined by the following set of - conditions: - </p> -<div class="itemizedlist"><ul class="itemizedlist" type="disc"> -<li class="listitem"><p>Parent class A defines a public virtual method named <code class="function">foo</code> and - provides a default implementation.</p></li> -<li class="listitem"><p>Child class B re-implements method <code class="function">foo</code>.</p></li> -<li class="listitem"><p>In the method B::foo, the child class B calls its parent class method A::foo.</p></li> -</ul></div> -<p> - There are many uses to this idiom: - </p> -<div class="itemizedlist"><ul class="itemizedlist" type="disc"> -<li class="listitem"><p>You need to change the behaviour of a class without modifying its code. You create - a subclass to inherit its implementation, re-implement a public virtual method to modify the behaviour - slightly and chain up to ensure that the previous behaviour is not really modified, just extended. - </p></li> -<li class="listitem"><p>You are lazy, you have access to the source code of the parent class but you don't want - to modify it to add method calls to new specialized method calls: it is faster to hack the child class - to chain up than to modify the parent to call down.</p></li> -<li class="listitem"><p>You need to implement the Chain Of Responsibility pattern: each object of the inheritance - tree chains up to its parent (typically, at the beginning or the end of the method) to ensure that - they each handler is run in turn.</p></li> -</ul></div> -<p> - I am personally not really convinced any of the last two uses are really a good idea but since this - programming idiom is often used, this section attempts to explain how to implement it. - </p> -<p> - To explicitly chain up to the implementation of the virtual method in the parent class, - you first need a handle to the original parent class structure. This pointer can then be used to - access the original class function pointer and invoke it directly. - <sup>[<a name="idp21694112" href="#ftn.idp21694112" class="footnote">11</a>]</sup> - </p> -<p>The function <code class="function"><a class="link" href="gobject-Type-Information.html#g-type-class-peek-parent" title="g_type_class_peek_parent ()">g_type_class_peek_parent</a></code> is used to access the original parent - class structure. Its input is a pointer to the class of the derived object and it returns a pointer - to the original parent class structure. The code below shows how you could use it: -</p> -<pre class="programlisting"> -static void -b_method_to_call (B *obj, int a) -{ - BClass *klass; - AClass *parent_class; - - klass = B_GET_CLASS (obj); - parent_class = g_type_class_peek_parent (klass); - - /* do stuff before chain up */ - - parent_class->method_to_call (obj, a); - - /* do stuff after chain up */ -} -</pre> -<p> - </p> -<div class="footnotes"> -<br><hr width="100" align="left"> -<div class="footnote"><p><sup>[<a id="ftn.idp21694112" href="#idp21694112" class="para">11</a>] </sup> - The <span class="emphasis"><em>original</em></span> adjective used in this sentence is not innocuous. To fully - understand its meaning, you need to recall how class structures are initialized: for each object type, - the class structure associated to this object is created by first copying the class structure of its - parent type (a simple <code class="function">memcpy</code>) and then by invoking the class_init callback on - the resulting class structure. Since the class_init callback is responsible for overwriting the class structure - with the user re-implementations of the class methods, we cannot merely use the modified copy of the parent class - structure stored in our derived instance. We want to get a copy of the class structure of an instance of the parent - class. - </p></div> -</div> -</div> -<div class="footer"> -<hr> - Generated by GTK-Doc V1.18</div> -</body> -</html>
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