Date popup form field doesn't show the default value correctly

Question

I am creating a custom form with "date_popup" form fields.
The only issue I have is that the default_value for the date popup form field shows only the first digit of the year, not the whole date.

Can anyone help with this?

Answer 1

Clive was absolutely right: The default value MUST be set using the date format "Y-m-d", such as with date('Y-m-d', $date).

The difference is that I used "Y-M-d" instead of "Y-m-d" for #default_value.

Answer 2

For Drupal 8:

use Drupal\Core\Datetime\DrupalDateTime;

$form['mydatefield']['widget'][0]['value']['#default_value'] = DrupalDateTime::createFromTimestamp(strtotime($mydatestring));