Exposing GTK3 custom widget properties in glade

I can add a custom widget to GTK, as shown here. Now I'd like to add properties to the custom widget and have them show up in glade. Is this possible?

I have added properties to the custom widget as shown here but the properties do not show up in glade.

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Update

It appears that the glade catalogue supports a <parameter-spec> element that can be used to define properties to be exposed within glade as shown below.

<glade-widget-class title="Awesome TextView" name="AwesomeTextView" generic-name="awesome_text_view">
    <properties>
        <property id="num_fidgets" name="Number of fidgets" default="4" save="False" custom-layout="True">
        <parameter-spec>
            <type>GParamInt</type>
            <min>4</min>
        </parameter-spec>
        <tooltip>The number of fidgets</tooltip>
        </property>
    </properties>
</glade-widget-class>

I have defined one such property but it does not show in glade. Rather I get the error message:

GLib-GObject-CRITICAL **: 16:07:45.433: g_object_set_is_valid_property: object class 'AwesomeTextView' has no property named 'num-fidgets'

Where the custom widget AwesomeTextView is essentially defined as:

class AwesomeTextView (Gtk.TextView):
    __gtype_name__ = 'AwesomeTextView'
    
    num_fidgets = GObject.Property(type=int, default='4', nick='num_Fidgets')

The <parameter-spec>s appear to be undocumented. Thankfully though there are examples of the the supported <type>s in the glade repo.

Correction: <parameter-spec>s are documented. This documentation can be supplemented with examples of the supported <type>s in the glade repo.

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Update2

Found the cause of the error. The default argument has the wrong type -- str instead of int. The property should be:

num_fidgets = GObject.Property(type=int, default=4, nick='num_Fidgets')

Glade no longer emits an error. But the property does not show up in the UI.

Overly complicated solution (See update for simpler solution)

Found the final piece. Do not set the <property> attribute custom-layout to "True" -- unless you know what are doing i.e. you know how to layout the property, properly (I don't, at least not yet). My advise, set custom-layout="False" in the updated catalogue shown below:

<glade-catalog name="awesome_text_view" library="gladepython" domain="glade-3" depends="gtk+">
    <init-function>glade_python_init</init-function>

    <glade-widget-classes>
        <glade-widget-class title="Awesome TextView" name="AwesomeTextView" generic-name="awesome_text_view">
            <properties>
                <property id="num_fidgets" name="Number of fidgets" default="4" save="True" custom-layout="False">
                    <parameter-spec>
                        <type>GParamInt</type>
                        <min>4</min>
                    </parameter-spec>
                    <tooltip>The number of fidgets</tooltip>
                </property>
            </properties>
        </glade-widget-class>
    </glade-widget-classes>

    <glade-widget-group name="Python" title="Python">
        <glade-widget-class-ref name="AwesomeTextView"/>
    </glade-widget-group>
</glade-catalog>

Result:

For completeness here is the sample custom widget class

import gi
gi.require_version("Gtk", "3.0")
from gi.repository import GObject
from gi.repository import Gtk

class AwesomeTextView(Gtk.TextView):
    __gtype_name__ = 'AwesomeTextView'
    num_fidgets = GObject.Property(type=int, default=4, nick='num_fidgets')

    def __init__(self):
        Gtk.TextView.__init__(self)

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Update

Turns out the nick argument in the property declaration

num_fidgets = GObject.Property(type=int, default=4, nick='num_fidgets')

is all that's required to for the property to show up in the glade UI. The element <properties> would be more appropriate for more complicated values e.g. enums. I'm leaving the more complicated answer in place in the event that its of use to anyone.