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cleaning under doxygen control: one_rule/algebra
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<section id="widget-templates">
<h1>Widget Templates<a class="headerlink" href="#widget-templates" title="Permalink to this headline">#</a></h1>
<p>GTK provides a way to describe UIs using definition files and the
<a class="reference external" href="https://docs.gtk.org/gtk4/class.Builder.html">GtkBuilder</a> API. Typically
you will need to create a <code class="docutils literal notranslate"><span class="pre">GtkBuilder</span></code> object instance and load the UI
definition XML file, extract the generated objects, and store references to
them inside your own types and data structures.</p>
<p>To automate this work, GTK also provides <em>templates</em>: a way to automatically
load the UI definition of a GTK widget type, bind the objects described in the
XML to fields in the widget instance, and automatically manage their lifetime.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>UI definitions can describe any object type that inherits from GObject.
Only widgets can have templates, but templates can contain any object.</p>
</div>
<section id="using-a-template">
<h2>Using a template<a class="headerlink" href="#using-a-template" title="Permalink to this headline">#</a></h2>
<p>Templates are bound to a type, and are loaded whenever a new instance of that
type is created.</p>
<p>In order to use a template you will need to register it at class initialization
time. Typically you will have your UI definition file bundled with your binary
using <a class="reference external" href="https://docs.gtk.org/gio/struct.Resource.html">GResource</a>, in order
to reliably access it from your project.</p>
<p>As an example, we have a composite widget type that contains two children:</p>
<ul class="simple">
<li><p>an entry</p></li>
<li><p>a button</p></li>
</ul>
<p>Its UI definition file is going to be:</p>
<div class="highlight-xml notranslate"><div class="highlight"><pre><span></span><span class="nt">&lt;interface&gt;</span>
<span class="nt">&lt;template</span> <span class="na">class=</span><span class="s">&quot;ExampleWidget&quot;</span> <span class="na">parent=</span><span class="s">&quot;GtkWidget&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkEntry&quot;</span> <span class="na">id=</span><span class="s">&quot;entry&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;/object&gt;</span>
<span class="nt">&lt;/child&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkButton&quot;</span> <span class="na">id=</span><span class="s">&quot;button&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">&quot;label&quot;</span><span class="nt">&gt;</span>Hello<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;/object&gt;</span>
<span class="nt">&lt;/child&gt;</span>
<span class="nt">&lt;/template&gt;</span>
<span class="nt">&lt;/interface&gt;</span>
</pre></div>
</div>
<p>and it is going to be saved as a <code class="docutils literal notranslate"><span class="pre">GResource</span></code> under the <code class="docutils literal notranslate"><span class="pre">/com/example/widget.ui</span></code>
path.</p>
<div class="sphinx-tabs docutils container">
<div aria-label="Tabbed content" class="closeable" role="tablist"><button aria-controls="panel-0-0-0" aria-selected="true" class="sphinx-tabs-tab" id="tab-0-0-0" name="0-0" role="tab" tabindex="0">C</button></div><div aria-labelledby="tab-0-0-0" class="sphinx-tabs-panel" id="panel-0-0-0" name="0-0" role="tabpanel" tabindex="0"><ol class="arabic simple">
<li><p>Add the template registration to your <code class="docutils literal notranslate"><span class="pre">class_init</span></code> function</p></li>
</ol>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">G_DECLARE_FINAL_TYPE</span><span class="w"> </span><span class="p">(</span><span class="n">ExampleWidget</span><span class="p">,</span><span class="w"> </span><span class="n">example_widget</span><span class="p">,</span><span class="w"> </span><span class="n">EXAMPLE</span><span class="p">,</span><span class="w"> </span><span class="n">WIDGET</span><span class="p">,</span><span class="w"> </span><span class="n">GtkWidget</span><span class="p">)</span><span class="w"></span>
<span class="k">struct</span><span class="w"> </span><span class="nc">_ExampleWidget</span><span class="w"></span>
<span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">GtkWidget</span><span class="w"> </span><span class="n">parent_type</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="n">GtkWidget</span><span class="w"> </span><span class="o">*</span><span class="n">entry</span><span class="p">;</span><span class="w"></span>
<span class="w"> </span><span class="n">GtkWidget</span><span class="w"> </span><span class="o">*</span><span class="n">button</span><span class="p">;</span><span class="w"></span>
<span class="p">};</span><span class="w"></span>
<span class="n">G_DEFINE_TYPE</span><span class="w"> </span><span class="p">(</span><span class="n">ExampleWidget</span><span class="p">,</span><span class="w"> </span><span class="n">example_widget</span><span class="p">,</span><span class="w"> </span><span class="n">GTK_TYPE_WIDGET</span><span class="p">)</span><span class="w"></span>
<span class="k">static</span><span class="w"> </span><span class="kt">void</span><span class="w"></span>
<span class="n">example_widget_class_init</span><span class="w"> </span><span class="p">(</span><span class="n">ExampleWidgetClass</span><span class="w"> </span><span class="o">*</span><span class="n">klass</span><span class="p">)</span><span class="w"></span>
<span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">GtkWidgetClass</span><span class="w"> </span><span class="o">*</span><span class="n">widget_class</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">GTK_WIDGET_CLASS</span><span class="w"> </span><span class="p">(</span><span class="n">klass</span><span class="p">);</span><span class="w"></span>
<span class="hll"><span class="w"> </span><span class="n">gtk_widget_class_set_template_from_resource</span><span class="w"> </span><span class="p">(</span><span class="n">widget_class</span><span class="p">,</span><span class="w"></span>
</span><span class="hll"><span class="w"> </span><span class="s">&quot;/com/example/widget.ui&quot;</span><span class="p">);</span><span class="w"></span>
</span><span class="p">}</span><span class="w"></span>
</pre></div>
</div>
<ol class="arabic simple" start="2">
<li><p>Bind the widgets defined inside the template file to the corresponding
members of the widget’s instance data structure</p></li>
</ol>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="kt">void</span><span class="w"></span>
<span class="nf">example_widget_class_init</span><span class="w"> </span><span class="p">(</span><span class="n">ExampleWidgetClass</span><span class="w"> </span><span class="o">*</span><span class="n">klass</span><span class="p">)</span><span class="w"></span>
<span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">GtkWidgetClass</span><span class="w"> </span><span class="o">*</span><span class="n">widget_class</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">GTK_WIDGET_CLASS</span><span class="w"> </span><span class="p">(</span><span class="n">klass</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">gtk_widget_class_set_template_from_resource</span><span class="w"> </span><span class="p">(</span><span class="n">widget_class</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="s">&quot;/com/example/widget.ui&quot;</span><span class="p">);</span><span class="w"></span>
<span class="hll"><span class="w"> </span><span class="n">gtk_widget_class_bind_template_child</span><span class="w"> </span><span class="p">(</span><span class="n">widget_class</span><span class="p">,</span><span class="w"> </span><span class="n">ExampleWidget</span><span class="p">,</span><span class="w"> </span><span class="n">entry</span><span class="p">);</span><span class="w"></span>
</span><span class="hll"><span class="w"> </span><span class="n">gtk_widget_class_bind_template_child</span><span class="w"> </span><span class="p">(</span><span class="n">widget_class</span><span class="p">,</span><span class="w"> </span><span class="n">ExampleWidget</span><span class="p">,</span><span class="w"> </span><span class="n">button</span><span class="p">);</span><span class="w"></span>
</span><span class="p">}</span><span class="w"></span>
</pre></div>
</div>
<ol class="arabic simple" start="3">
<li><p>Initialize the template children when initializing the widgdet instance</p></li>
</ol>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="kt">void</span><span class="w"></span>
<span class="nf">example_widget_init</span><span class="w"> </span><span class="p">(</span><span class="n">ExampleWidget</span><span class="w"> </span><span class="o">*</span><span class="n">self</span><span class="p">)</span><span class="w"></span>
<span class="p">{</span><span class="w"></span>
<span class="hll"><span class="w"> </span><span class="n">gtk_widget_init_template</span><span class="w"> </span><span class="p">(</span><span class="n">GTK_WIDGET</span><span class="w"> </span><span class="p">(</span><span class="n">self</span><span class="p">));</span><span class="w"></span>
</span>
<span class="w"> </span><span class="c1">// It is now possible to access self-&gt;entry and self-&gt;button</span>
<span class="p">}</span><span class="w"></span>
</pre></div>
</div>
<ol class="arabic simple" start="4">
<li><p>Clear the template children when disposing the widget instance</p></li>
</ol>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="hll"><span class="k">static</span><span class="w"> </span><span class="kt">void</span><span class="w"></span>
</span><span class="hll"><span class="nf">example_widget_dispose</span><span class="w"> </span><span class="p">(</span><span class="n">GObject</span><span class="w"> </span><span class="o">*</span><span class="n">gobject</span><span class="p">)</span><span class="w"></span>
</span><span class="hll"><span class="p">{</span><span class="w"></span>
</span><span class="hll"><span class="w"> </span><span class="n">gtk_widget_dispose_template</span><span class="w"> </span><span class="p">(</span><span class="n">GTK_WIDGET</span><span class="w"> </span><span class="p">(</span><span class="n">gobject</span><span class="p">),</span><span class="w"> </span><span class="n">EXAMPLE_TYPE_WIDGET</span><span class="p">);</span><span class="w"></span>
</span><span class="hll">
</span><span class="hll"><span class="w"> </span><span class="n">G_OBJECT_CLASS</span><span class="w"> </span><span class="p">(</span><span class="n">example_widget_parent_class</span><span class="p">)</span><span class="o">-&gt;</span><span class="n">dispose</span><span class="w"> </span><span class="p">(</span><span class="n">gobject</span><span class="p">);</span><span class="w"></span>
</span><span class="hll"><span class="p">}</span><span class="w"></span>
</span>
<span class="k">static</span><span class="w"> </span><span class="kt">void</span><span class="w"></span>
<span class="nf">example_widget_class_init</span><span class="w"> </span><span class="p">(</span><span class="n">ExampleWidgetClass</span><span class="w"> </span><span class="o">*</span><span class="n">klass</span><span class="p">)</span><span class="w"></span>
<span class="p">{</span><span class="w"></span>
<span class="hll"><span class="w"> </span><span class="n">G_OBJECT_CLASS</span><span class="w"> </span><span class="p">(</span><span class="n">klass</span><span class="p">)</span><span class="o">-&gt;</span><span class="n">dispose</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">example_widget_dispose</span><span class="p">;</span><span class="w"></span>
</span>
<span class="w"> </span><span class="n">GtkWidgetClass</span><span class="w"> </span><span class="o">*</span><span class="n">widget_class</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">GTK_WIDGET_CLASS</span><span class="w"> </span><span class="p">(</span><span class="n">klass</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">gtk_widget_class_set_template_from_resource</span><span class="w"> </span><span class="p">(</span><span class="n">widget_class</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="s">&quot;/com/example/widget.ui&quot;</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">gtk_widget_class_bind_template_child</span><span class="w"> </span><span class="p">(</span><span class="n">widget_class</span><span class="p">,</span><span class="w"> </span><span class="n">ExampleWidget</span><span class="p">,</span><span class="w"> </span><span class="n">entry</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="n">gtk_widget_class_bind_template_child</span><span class="w"> </span><span class="p">(</span><span class="n">widget_class</span><span class="p">,</span><span class="w"> </span><span class="n">ExampleWidget</span><span class="p">,</span><span class="w"> </span><span class="n">button</span><span class="p">);</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</pre></div>
</div>
</div></div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>It is not necessary to bind all the template children defined in the UI
file. You can use <code class="docutils literal notranslate"><span class="pre">gtk_widget_get_template_child()</span></code> to access a named
template child at run time. If you find yourself accessing the same
template child multiple times, it is more efficient to store the reference
inside your instance data structure.</p>
</div>
</section>
<section id="when-to-use-templates">
<h2>When to use templates<a class="headerlink" href="#when-to-use-templates" title="Permalink to this headline">#</a></h2>
<p>Templates are useful as a way to keep code maintainable, and reduce the size
of UI definition files. If your UI definitions become increasingly complex or
include too many levels of nested widgets, then you should consider moving
blocks of functionality and related widgets into their own composite template,
and then instantiate the template widget from their parent’s UI definition. For
instance, given this UI definition:</p>
<div class="highlight-xml notranslate"><div class="highlight"><pre><span></span><span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkStack&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkStackPage&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">&quot;child&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">&quot;orientation&quot;</span><span class="nt">&gt;</span>vertical<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkButton&quot;</span><span class="nt">&gt;</span>
<span class="cm">&lt;!-- ... --&gt;</span>
</pre></div>
</div>
<p>You may want to move the <code class="docutils literal notranslate"><span class="pre">GtkBox</span></code> that is the child of the stack page into
its own composite widget:</p>
<div class="highlight-xml notranslate"><div class="highlight"><pre><span></span><span class="nt">&lt;template</span> <span class="na">class=</span><span class="s">&quot;ButtonsPage&quot;</span> <span class="na">parent=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">&quot;orientation&quot;</span><span class="nt">&gt;</span>vertical<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkButton&quot;</span><span class="nt">&gt;</span>
<span class="cm">&lt;!-- ... --&gt;</span>
</pre></div>
</div>
<p>And then reference it from the main UI definition:</p>
<div class="highlight-xml notranslate"><div class="highlight"><pre><span></span><span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkStack&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkStackPage&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">&quot;child&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;ButtonsPage&quot;</span><span class="nt">&gt;</span>
<span class="cm">&lt;!-- ... --&gt;</span>
</pre></div>
</div>
<p>After that, you may want to move the box with the stack into its own composite
widget:</p>
<div class="highlight-xml notranslate"><div class="highlight"><pre><span></span><span class="nt">&lt;template</span> <span class="na">class=</span><span class="s">&quot;StackBox&quot;</span> <span class="na">parent=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkStack&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkStackPage&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">&quot;child&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;ButtonsPage&quot;</span><span class="nt">&gt;</span>
<span class="cm">&lt;!-- ... --&gt;</span>
</pre></div>
</div>
<p>And reference it from the main UI definition:</p>
<div class="highlight-xml notranslate"><div class="highlight"><pre><span></span><span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;GtkBox&quot;</span><span class="nt">&gt;</span>
<span class="nt">&lt;child&gt;</span>
<span class="nt">&lt;object</span> <span class="na">class=</span><span class="s">&quot;StackBox&quot;</span><span class="nt">&gt;</span>
</pre></div>
</div>
<p>This way we have replace one big UI definition file with three smaller ones.</p>
</section>
</section>
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<ul>
<li><a class="reference internal" href="#">Widget Templates</a><ul>
<li><a class="reference internal" href="#using-a-template">Using a template</a></li>
<li><a class="reference internal" href="#when-to-use-templates">When to use templates</a></li>
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