TYPO3.Flow

note conversion is done in DateTimeConverter

The idea is to have a ViewHelper, which adds an additional hidden signed field which contains the valid date format (e.g. d.m.Y) after sending the form the string is then checked against the formatstring which was set for the field

thanks to Christian Müller (thumbsup) i got the relevant hint on how to do that:

<?php

namespace TYPO3\FLOW\ViewHelpers\Form;

use TYPO3\Fluid\Core\ViewHelper\Exception;

class DateTimeTextfieldViewHelper extends \TYPO3\Fluid\ViewHelpers\Form\AbstractFormFieldViewHelper {
    /**
     * @var string
     */
    protected $tagName = 'input';

    /**
     * Initialize the arguments.
     *
     * @return void
     * @api
     */
    public function initializeArguments() {
        parent::initializeArguments();
        $this->registerTagAttribute('disabled', 'string', 'Specifies that the input element should be disabled when the page loads');
        $this->registerTagAttribute('maxlength', 'int', 'The maxlength attribute of the input field (will not be validated)');
        $this->registerTagAttribute('readonly', 'string', 'The readonly attribute of the input field');
        $this->registerTagAttribute('size', 'int', 'The size of the input field');
        $this->registerTagAttribute('placeholder', 'string', 'Placeholder for the field');
        $this->registerArgument('errorClass', 'string', 'CSS class to set if there are errors for this view helper', FALSE, 'f3-form-error');
        $this->registerArgument('dateFormat', 'string', 'DateTime object attribute', FALSE, 'Y-m-d\TH:i:sP');
        $this->registerUniversalTagAttributes();
    }

    public function render($required = NULL, $type = 'text') {
        $name = $this->getName();
        $this->registerFieldNameForFormTokenGeneration($name);

        $this->tag->addAttribute('type', $type);
        $this->tag->addAttribute('name', $name . '[date]');

        /** @var \DateTime $value */
        $value = $this->getValue(FALSE);
        if(is_a($value, '\\DateTime')) {
            $valueString = $value->format($this->arguments['dateFormat']);
        } else {
            throw new Exception('Expected \\DateTime object, but got ' . gettype($value) . ' for ' . $this->getName());
        }

        if ($value !== NULL) {
            $this->tag->addAttribute('value', $valueString);
        }

        if ($required !== NULL) {
            $this->tag->addAttribute('required', 'required');
        }

        $this->setErrorClassAttribute();

        return $this->tag->render() . '<input type="hidden" value="' . htmlspecialchars($this->arguments['dateFormat']) . '" name="' . $this->getName() . '[dateFormat]" />';
    }
}