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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html> <head> <title> Writing a GtkWidget </title> <meta name="GENERATOR" content= "Modular DocBook HTML Stylesheet Version 1.45"> <link rel="HOME" title="GTK+ / Gnome Application Development" href="ggad.html"> <link rel="UP" title="Advanced GTK+/Gnome Techniques" href= "advanced.html"> <link rel="PREVIOUS" title="GtkStyle and Themes" href= "sec-style.html"> <link rel="NEXT" title="The GtkWidget Base Class" href= "z144.html"> </head> <body bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink= "#840084" alink="#0000FF"> <div class="NAVHEADER"> <table width="100%" border="0" bgcolor="#ffffff" cellpadding= "1" cellspacing="0"> <tr> <th colspan="4" align="center"> <font color="#000000" size="2">GTK+ / Gnome Application Development</font> </th> </tr> <tr> <td width="25%" bgcolor="#ffffff" align="left"> <a href="sec-style.html"><font color="#0000ff" size= "2"><b><<< Previous</b></font></a> </td> <td width="25%" colspan="2" bgcolor="#ffffff" align= "center"> <font color="#0000ff" size="2"><b><a href="ggad.html"> <font color="#0000ff" size="2"><b> Home</b></font></a></b></font> </td> <td width="25%" bgcolor="#ffffff" align="right"> <a href="z144.html"><font color="#0000ff" size="2"><b> Next >>></b></font></a> </td> </tr> </table> </div> <div class="CHAPTER"> <h1> <a name="CHA-WIDGET">Writing a <tt class="CLASSNAME"> GtkWidget</tt></a> </h1> <div class="TOC"> <dl> <dt> <b>Table of Contents</b> </dt> <dt> <a href="cha-widget.html#Z141">Overview</a> </dt> <dt> <a href="z144.html">The <tt class="CLASSNAME"> GtkWidget</tt> Base Class</a> </dt> <dt> <a href="z147.html">An Example: The <tt class= "CLASSNAME">GtkEv</tt> Widget</a> </dt> <dt> <a href="sec-widgetindetail.html"><tt class= "CLASSNAME">GtkWidget</tt> In Detail</a> </dt> <dt> <a href="z166.html"><tt class="CLASSNAME">GtkVBox</tt>: A Windowless Container</a> </dt> <dt> <a href="z170.html"><tt class="CLASSNAME"> GnomeAppBar</tt>: A Trivial Composite Widget</a> </dt> <dt> <a href="z171.html">Other Examples</a> </dt> </dl> </div> <p> This chapter describes how to write a new <tt class= "CLASSNAME">GtkWidget</tt>. A widget is any <span class= "STRUCTNAME">GtkObject</span> that derives from <tt class= "CLASSNAME">GtkWidget</tt>; before reading this chapter, you should be familiar with <a href="cha-objects.html">the chapter called <i>The GTK+ Object and Type System</i></a>. This chapter will discuss the details of <tt class= "CLASSNAME">GtkWidget</tt>, but will not re-explain <span class="STRUCTNAME">GtkObject</span> in general. You will also need to know something about GDK to write a widget; be sure to skim <a href="cha-gdk.html">the chapter called <i> GDK Basics</i></a> if you haven't. </p> <p> Widgets are easy to create; you only need to cut-and-paste the usual <span class="STRUCTNAME">GtkObject</span> boilerplate (instance and class initializers, a <span class="STRUCTNAME">get_type()</span> function, and so on), and then implement your widget's functionality. Writing new widgets is an important application development technique. </p> <p> After a brief overview, this chapter jumps straight to the implementation of a very simple widget called <tt class= "CLASSNAME">GtkEv</tt>. Then it takes a step back, describing widget implementation more systematically. It ends with more examples, taken from GTK+ itself. (It pays to become familiar with the GTK+ source code: often the easiest way to implement a widget is to subclass or slightly modify the most similar stock GTK+ widget. Of course, you must comply with the terms of GTK+'s license if you cut-and-paste code from the library.) </p> <div class="SECT1"> <h1 class="SECT1"> <a name="Z141">Overview</a> </h1> <p> This section gives a brief overview, including the different kinds of widget you might encounter, and the general functionality a <tt class="CLASSNAME"> GtkWidget</tt> is required to have. </p> <div class="SECT2"> <h2 class="SECT2"> <a name="Z142">Kinds of Widget</a> </h2> <p> The term "widget" is really very broad, since it encompasses any object that implements the <tt class= "CLASSNAME">GtkWidget</tt> interface. There are many ways to classify widgets: </p> <ul> <li> <p> <i class="FIRSTTERM">Containers</i> are widgets that store other widgets inside, such as the boxes and tables described in <a href="cha-gtk.html">the chapter called <i>GTK+ Basics</i></a>. As <a href= "cha-gtk.html">the chapter called <i>GTK+ Basics</i></a> discussed, containers can be subdivided into those that add functionality to a single child (<tt class="CLASSNAME">GtkButton</tt>, <tt class="CLASSNAME">GtkFrame</tt>, <tt class= "CLASSNAME">GtkEventBox</tt>, etc.), and those that manage layout for multiple children (<tt class= "CLASSNAME">GtkBox</tt>, <tt class="CLASSNAME"> GtkTable</tt>, etc.). Container widgets are harder to implement than "plain" widgets because the <tt class="CLASSNAME">GtkContainer</tt> interface must be implemented in addition to the <tt class= "CLASSNAME">GtkWidget</tt> interface. </p> </li> <li> <p> <i class="FIRSTTERM">Composite</i> widgets are containers that already contain a useful collection of child widgets in a nice package. For example, the <span class="STRUCTNAME"> GtkFileSelection</span> widget is a subclass of <span class="STRUCTNAME">GtkWindow</span> that already contains a list widget to show files, dialog buttons, and so on. Widgets like this are easy to write, and are a convenient way to code applications. You could write a "MainWindow" widget for your main application window, for example, and then create a new instance of the widget whenever the user opens a new document. <tt class= "CLASSNAME">GnomeApp</tt> and <tt class= "CLASSNAME">GnomeDialog</tt> are two important composite widgets in Gnome. </p> </li> <li> <p> Non-container widgets can be actual controls (buttons, scroll bars, etc.), information displays (<tt class="CLASSNAME">GtkLabel</tt>), or decorative flourishes (<tt class= "CLASSNAME">GtkSeparator</tt>, for example). As <a href="cha-gtk.html">the chapter called <i>GTK+ Basics</i></a> briefly mentioned, there are two major ways to implement widgets: most widgets (those that need to receive events or draw their own background) have an associated <span class= "STRUCTNAME">GdkWindow</span>; "no window" widgets draw on their parent container. Widgets without windows are implemented slightly differently. All containers have a <span class="STRUCTNAME"> GdkWindow</span> (since widgets without one might need to draw on it, among other reasons). </p> </li> </ul> <p> This chapter presents several widgets as examples, including a <tt class="CLASSNAME">GtkEv</tt> widget written especially for this book, <tt class= "CLASSNAME">GtkVBox</tt> from GTK+, and <tt class= "CLASSNAME">GnomeAppBar</tt> from <tt class= "APPLICATION">libgnomeui</tt>. </p> </div> <div class="SECT2"> <h2 class="SECT2"> <a name="Z143">What a Widget Does</a> </h2> <p> A minimal widget implements the following (though <tt class="CLASSNAME">GtkWidget</tt>'s default implementation may be sufficient in many cases): </p> <ul> <li> <p> Creation and destruction; this means the usual <span class="STRUCTNAME">GtkObject</span> boilerplate (instance and class initializers, shutdown, destroy and finalize methods). See <a href="cha-objects.html">the chapter called <i>The GTK+ Object and Type System</i></a>, especially <a href="cha-objects.html#SEC-OBJECTSTRUCTS">the section called <i>Object and Class Structures</i> in the chapter called <i>The GTK+ Object and Type System</i></a> and <a href="sec-finalization.html"> the section called <i>Object Finalization</i> in the chapter called <i>The GTK+ Object and Type System</i></a>. Also see <a href= "z57.html#WIDGETLIFECYCLE">the section called <i> Widget Life Cycle</i> in the chapter called <i>GTK+ Basics</i></a>. </p> </li> <li> <p> The realize/map/unmap/unrealize cycle discussed in <a href="z57.html#SEC-REALIZINGSHOWING">the section called <i>Realizing, Mapping, and Showing</i> in the chapter called <i>GTK+ Basics</i></a>. Widgets must be able to create and uncreate their associated X resources any number of times, and they must be able to show and hide themselves any number of times. </p> </li> <li> <p> Geometry negotiation, discussed in <a href= "sec-containers.html#SEC-SIZENEGOTIATION">the section called <i>Size Allocation</i> in the chapter called <i>GTK+ Basics</i></a>. Your widget must respond to size requests, and honor size allocations. </p> </li> <li> <p> Drawing; widgets must be able to draw themselves on the screen. For container widgets, the widget itself may be invisible but it must ensure child widgets are drawn. </p> </li> <li> <p> The widget's unique functionality. Typically this means implementing handlers for some of the widget's event signals. </p> </li> </ul> </div> </div> </div> <div class="NAVFOOTER"> <br> <br> <table width="100%" border="0" bgcolor="#ffffff" cellpadding= "1" cellspacing="0"> <tr> <td width="25%" bgcolor="#ffffff" align="left"> <a href="sec-style.html"><font color="#0000ff" size= "2"><b><<< Previous</b></font></a> </td> <td width="25%" colspan="2" bgcolor="#ffffff" align= "center"> <font color="#0000ff" size="2"><b><a href="ggad.html"> <font color="#0000ff" size="2"><b> Home</b></font></a></b></font> </td> <td width="25%" bgcolor="#ffffff" align="right"> <a href="z144.html"><font color="#0000ff" size="2"><b> Next >>></b></font></a> </td> </tr> <tr> <td colspan="2" align="left"> <font color="#000000" size="2"><b><span class= "STRUCTNAME">GtkStyle</span> and Themes</b></font> </td> <td colspan="2" align="right"> <font color="#000000" size="2"><b>The <tt class= "CLASSNAME">GtkWidget</tt> Base Class</b></font> </td> </tr> </table> </div> </body></html>⌨️ 快捷键说明
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