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<th width="60%" align="center">Chapter 26. Gtk::Builder</th>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-builder-accessing-widgets"></a>Accessing widgets</h2></div></div></div>
<p>
To access a widget, for instance to show a dialog, use
the <code class="methodname">get_widget()</code> method, providing the widget's name.
This name should be specified in the <span class="application">Cambalache</span>
window. If the widget could not be found, or is of the wrong type, then the
pointer will be set to <code class="literal">nullptr</code>.
</p>
<p>
The dialogs in this chapter are derived from <code class="classname">Gtk::Window</code>
because <code class="classname">Gtk::Dialog</code> is deprecated since <span class="application">gtkmm</span> 4.10.
</p>
<pre class="programlisting"><code class="code">auto pDialog = builder->get_widget<Gtk::Window>("DialogBasic");
</code></pre>
<p>
<code class="classname">Gtk::Builder</code> checks for a null pointer, and checks
that the widget is of the expected type, and will show warnings on the command
line about these.
</p>
<p>
Remember that you are not instantiating a widget with
<code class="methodname">get_widget()</code>, you are just obtaining a pointer to one that
already exists. You will always receive a pointer to the same instance when you
call <code class="methodname">get_widget()</code> on the same
<code class="classname">Gtk::Builder</code>, with the same widget name. The
widgets are instantiated during <code class="methodname">Gtk::Builder::create_from_file()</code>.
</p>
<p>
<code class="methodname">get_widget()</code> returns child widgets that are
<code class="function">manage()</code>ed (see the <a class="link" href="chapter-memory.html" title="Chapter 25. Memory management">Memory
Management</a> chapter), so they will be deleted when their parent
container is deleted. <code class="classname">Window</code>s (such as <code class="classname">Dialog</code>s)
cannot be managed because they have no parent container, so you must delete them at
some point. The documentation of <code class="classname">Gtk::Builder</code> has more to say
about the memory management of different kinds of objects.
</p>
<p><a class="ulink" href="https://gnome.pages.gitlab.gnome.org/gtkmm/classGtk_1_1Builder.html" target="_top">Reference</a></p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="builder-example-basic"></a>Example</h3></div></div></div>
<p>
This simple example shows how to load a <code class="filename">.ui</code>
file at runtime and access the widgets with <code class="classname">Gtk::Builder</code>.
</p>
<p><a class="ulink" href="https://gitlab.gnome.org/GNOME/gtkmm-documentation/tree/master/examples/book/builder/basic" target="_top">Source Code</a></p>
<p>File: <code class="filename">main.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#include <gtkmm.h>
#include <iostream>
namespace
{
Gtk::Window* pDialog = nullptr;
Glib::RefPtr<Gtk::Application> app;
void on_button_clicked()
{
if (pDialog)
pDialog->set_visible(false); // set_visible(false) will cause Gtk::Application::run() to end.
}
void on_app_activate()
{
// Load the GtkBuilder file and instantiate its widgets:
auto refBuilder = Gtk::Builder::create();
try
{
refBuilder->add_from_file("basic.ui");
}
catch(const Glib::FileError& ex)
{
std::cerr << "FileError: " << ex.what() << std::endl;
return;
}
catch(const Glib::MarkupError& ex)
{
std::cerr << "MarkupError: " << ex.what() << std::endl;
return;
}
catch(const Gtk::BuilderError& ex)
{
std::cerr << "BuilderError: " << ex.what() << std::endl;
return;
}
// Get the GtkBuilder-instantiated dialog:
pDialog = refBuilder->get_widget<Gtk::Window>("DialogBasic");
if (!pDialog)
{
std::cerr << "Could not get the dialog" << std::endl;
return;
}
// Get the GtkBuilder-instantiated button, and connect a signal handler:
auto pButton = refBuilder->get_widget<Gtk::Button>("quit_button");
if (pButton)
pButton->signal_clicked().connect([] () { on_button_clicked(); });
// It's not possible to delete widgets after app->run() has returned.
// Delete the dialog with its child widgets before app->run() returns.
pDialog->signal_hide().connect([] () { delete pDialog; });
app->add_window(*pDialog);
pDialog->set_visible(true);
}
} // anonymous namespace
int main(int argc, char** argv)
{
app = Gtk::Application::create("org.gtkmm.example");
// Instantiate a dialog when the application has been activated.
// This can only be done after the application has been registered.
// It's possible to call app->register_application() explicitly, but
// usually it's easier to let app->run() do it for you.
app->signal_activate().connect([] () { on_app_activate(); });
return app->run(argc, argv);
}
</code></pre>
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