silverstripe overwrite function of dataobject - silverstripe

Question

I want to extend the DataObject (EditableDateField) of a module that I use (UserDefinedForms). There I want to overwrite a certain method (getFormField). I was trying to extend with DataExtension. But it does not work.
Here the code...
config.php:
EditableDateField::add_extension("CustomEditableDateField");
CustomEditableDateField:
class CustomEditableDateField extends DataExtension {
public function getFormField() {
//test is function called
echo 'test';
exit();
}
}
Also I tried to use Object::useCustomClass in the config to replace the whole EditableDateField with my CustomClass, but also no success.
What is the best way to do that?
Many thanx,
Florian

Answer 1

To do what you are wanting to achieve, you don't need to extend EditableDateField.
What you are looking for is EditableDateField_FormField which extends DateField. DateField does the heavy lifting for generating the HTML and doing the validation etc. One thing that DateField does have is a static variable called default_config which looks like this:
static $default_config = array(
'showcalendar' => false,
'jslocale' => null,
'dmyfields' => false,
'dmyseparator' => ' <span class="separator">/</span> ',
'dmyplaceholders' => true,
'dateformat' => null,
'datavalueformat' => 'yyyy-MM-dd',
'min' => null,
'max' => null,
);
Using the configuration system in Silverstripe, you can change the default dateformat to your dd.MM.yyyy format by using:
EditableDateField_FormField:
default_config:
'dateformat': 'dd.MM.yyyy'
You will want to use EditableDateField_FormField like my example above rather than change the default_config of DateField itself otherwise you may encounter issues in the CMS.
Technical Description
This works due to the constructor of DateField setting the instance config to the value of the default_config.
Because the value of dateformat is normally NULL in default_config, an if-statement passes which causes dateformat to be set the result from i18n::get_date_format().