Exposing GTK3 custom widget properties in glade

Question

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.

Answer 1

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.