pos/barcodes_generate/views/view_product_product.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
Copyright (C) 2016-Today: GRAP (http://www.grap.coop)
@author Sylvain LE GAL (https://twitter.com/legalsylvain)
License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
-->

<openerp><data>

    <record id="view_product_product_form" model="ir.ui.view">
        <field name="model">product.product</field>
        <field name="inherit_id" ref="product.product_normal_form_view"/>
        <field name="arch" type="xml">
            <field name="default_code" position="after">
                <field name="barcode_rule_id"
                    domain="[('is_product_available', '=', True)]"
                    groups="barcodes_generate.generate_product_barcode" colspan="2"
                    attrs="{'readonly': [('ean13', '!=', False)]}"/>
                <field name="barcode_base" attrs="{'invisible': [('barcode_rule_id', '=', False)], 'readonly': [('ean13', '!=', False)]}"
                    groups="barcodes_generate.generate_product_barcode" colspan="2"/>
                <button name="generate_barcode" type="object" string="Generate Barcode"
                    attrs="{'invisible': ['|','|', ('ean13', '!=', False), ('barcode_rule_id', '=', False), ('barcode_base', '=', 0)]}"
                    groups="barcodes_generate.generate_product_barcode" colspan="2"/>
            </field>
        </field>
    </record>

</data></openerp>