hyperlink in openerp tree view

hyperlink in openerp tree view

I want to add a link with ftp url in my tree view. i tested with adding
widget="url" in my xml ,but its not working. Please help my code is
<tree string="File Names" >
<field name="time_created" string="Time Created"/>
<field name="size" string="Size"/>
<field name="file_name"/>
<field name="file_path" widget="url"/>
</tree>
class filedata(osv.osv):
_name = 'filedata'
_log_access = False
_columns = {
'file_name' : fields.char('Name'),
'file_path' : fields.char('File Path'),
'time_created' : fields.datetime('Date Time'),
'size' : fields.char('Size')
}