Silverstripe add UploadField to ModelAdmin failed

Question

I am trying to add an UploadField to ModelAdmin by creating an extension, after the GridFieldList. But I always get an error " Call to a member function FormAction() on a non-object in ..../framework/forms/FormField.php on line 161". I can add TextField,DropdownField without any problems, but no luck with UploadField. Did I miss something?

<code>
    class MyExtension extends Extension{
        public static $has_one = array(
            'ImportCSV' => 'File'
        );
        public function updateEditForm($form){
            $fields = $form->Fields();
            $fields->push(
                new TextField('Title', 'Title')
            );//This one works
            $fields->push(
                new UploadField('ImportCSV', 'Import CSV')
            );//This one not working
        }
    }
</code>

Answer 1

If you're writing an Extension (Specifically a DataExtension) then you'd use updateCMSFields($fields) which is passed an instance of FieldList by reference.

But to add the UploadField as I think you want, either add it to a DataExtension that extends (decorates) File in a call to updateCMSFields() or change extends Extension to extends DataExtension in your example above, and run dev/build flush=all