Hi, was running into problems with the MultiSelectField using pre-selected values. Applying the following fixes helped:

Lines 39-42 of MultiSelectField.php:

foreach($source as $index => $item) {
	$selected = (isset($value[$index])) ? 'selected="selected"' : ''; // added '="selected"', wasn't parsing
	$content .= "<option $selected value=\"$index\">".Convert::raw2xml($item)."</option>"; // converted $item to xml for parsing
}

Also worth having an example of how to pre-select values:

new MultiSelectField('Fruit', 'Favorite Fruit', array('1'=>'apple','2'=>'pear'), array('1'=>true))

Thanks for posting about this problem, rwestera. Unfortunately, your fix didn't do the trick for me. For some reason, I can't seem to set the value of the MultiSelectField until after it has already been initialized, where it looks like this needs to be done during initialization.

If I add a var_dump() to the Field() method in the MultiSelectField class for the selected values, it returns an empty array every time. But if I add the field using the following code:

$oFields->addFieldToTab('Root.PreferredProducts', $oPreferredProducts = new MultiSelectField(
	'PreferredProducts', 
	'Voorkeursproducten', 
	$oProducts->map('ID', 'Title'), 
	$aPreselectedProducts
));

var_dump($oPreferredProducts->getSelected());

The var_dump() returns an array with all of the options I passed (in $aPreselectedProducts), but they aren't selected at all in the HTML or on the screen!

In the end I went the ugly route by using the following code:

$jsSelectOptions = "";
foreach ($oPreferredProducts as $oProduct) {
	// Ugly JS fix
	$jsSelectOptions .= "jQuery('#Root_PreferredProducts select.multiselect-unselected option[value=\"".$oProduct->ID."\"]').attr('selected', 'selected');".chr(10);
}


// Preselect all default products and fire the click event for the "Add" button
Requirements::customScript("
	(function($) {
		".$jsSelectOptions."
		$('#Root_PreferredProducts .multiselect-add').click();
	})(jQuery);
");