AdwToolbarView needs special child types
AdwToolbarView has a property for content and two child with type top and bottom. Now when adding a child there is no option to change the child type.
<object class="AdwToolbarView">
<child type="top">
<object class="AdwHeaderBar"/>
</child>
<property name="content">
<object class="AdwPreferencesPage">
<!-- ... -->
</object>
</property>
<child type="bottom">
<object class="GtkBox"/>
</child>
</object>
Thank you for the great work!