Lookup by widget id in Widget template - gtk3

Question

There's a way of lookup by widget's id in widget template ?
by "widget template" I mean gtk_widget_class_set_template_from_resource
I've tried define following function in window class:
GtkWidget *
lookup_widget (CustomAppWindow *win,
const char *name)
{
return GTK_WIDGET (gtk_widget_get_template_child (GTK_WIDGET (win),
GTK_TYPE_WIDGET,
name));
}
but the gtk_widget_get_template_child always returns null.

Answer 1

calling gtk_widget_get_template_child() should never return NULL — but you should rarely have to call that function in the first place.
the correct way to access objects defined with GTK widget templates is to add a member to your instance data structure with the same name as in the XML definition, and then call gtk_widget_class_bind_template_child().
for instance, given the following XML description:
<interface>
<template class="FooWidget" parent="GtkBox">
<property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
<property name="spacing">4</property>
<child>
<object class="GtkButton" id="hello_button">
<property name="label">Hello World</property>
<signal name="clicked" handler="hello_button_clicked" object="FooWidget" swapped="yes"/>
</object>
</child>
<child>
<object class="GtkButton" id="goodbye_button">
<property name="label">Goodbye World</property>
</object>
</child>
</template>
</interface>
when creating your widget instance you typically will add two GtkWidget members in the instance data structure, such as:
typedef struct _FooWidget {
GtkBox parent_instance;
GtkWidget *hello_button;
GtkWidget *goodbye_button;
} FooWidget;
from your class initialization function, you will have to call the gtk_widget_class_bind_template_child() function after setting the template:
static void
foo_widget_class_init (FooWidgetClass *klass)
{
// ...
gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (klass),
"/com/example/foo/widget.ui");
gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (klass),
FooWidget, hello_button);
gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (klass),
FooWidget, goodbye_button);
}
the template machinery inside GTK+ will ensure that the fields are set on instance initialization, and unset on instance finalization. this means that you can access those fields from your instance init right after you called gtk_widget_init_template():
static void
foo_widget_init (FooWidget *self)
{
gtk_widget_init_template (GTK_WIDGET (self));
// now you can access self->hello_button and self->goodbye_button
}
if you are not writing an application, or you want to hide the components of your composite widget from your instance structure, you can use a private structure and call gtk_widget_class_bind_template_private_child() instead.
remember you can also bind functions defined in your local scope to signal handlers defined in the XML, using gtk_widget_class_bind_template_callback().