title: Function on_change openerp8 not work
body: <p>I want to add a column where I calculate the sum of the two columns but it doesn't work here is my code</p>
  
  <p>test.py:</p>
  
  <pre><code>from openerp.osv import fields, osv
  class sale_order_line(osv.osv):
  _inherit = 'account.bank.statement.line'
  _name = 'account.bank.statement.line'
  _columns = {
  'colx': fields.float(),
  'coly': fields.float(),
  }
  def onchange_result(self, cr, uid, ids, colx, amount, context=None):
      res = {}
      if amount and colx:
          res['coly'] = amount + colx
      return {'value': res}
  </code></pre>
  
  <p>test.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;openerp&gt;
     &lt;data&gt;
        &lt;record model="ir.ui.view" id="account_statement_instructor1_form_viewfzz"&gt;
          &lt;field name="name"&gt;account.statement.form.viewfzz&lt;/field&gt;
          &lt;field name="model"&gt;account.bank.statement&lt;/field&gt;
          &lt;field name="inherit_id" ref="account.view_bank_statement_formfz"/&gt;
          &lt;field name="arch" type="xml"&gt;
              &lt;xpath expr="//sheet/notebook/page/field[@name='line_ids']/tree/field[@name='date']" position="after"&gt;
              &lt;field name="colx" on_change="onchange_result(amount, colx)"/&gt;
              &lt;field name="amount" on_change="onchange_result(amount, colx)"/&gt;
              &lt;field name="coly"/&gt;
             &lt;/xpath&gt;
          &lt;/field&gt;
        &lt;/record&gt;&lt;/data&gt;&lt;/openerp&gt;
  </code></pre>
  
  <p>Thank you </p>