cooperative-market/beesdoo_purchase_manual_date_planned/views/purchase_order.xml

<openerp>
    <data>
        <record model="ir.ui.view" id="beesdoo_purchase_order_form_view">
            <field name="name">beesdoo.purchase.order.form.view</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form" />
            <field name="arch" type="xml">
                <xpath expr="//field[@name='date_planned']/../../div" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>
                <xpath expr="//label[@for='date_planned']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>
                <xpath expr="//tree/field[@name='date_planned']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>
                <field name="date_order" position="after">
                    <field name="manual_date_planned" attrs="{'readonly': [('state', 'not in', ('draft', 'sent'))]}" />
                </field>
            </field>
        </record>
    </data>
</openerp>