How do you set an ID for FieldGroup???
This doesnt work: (and neigther FieldGroup::create)

$CFGroup = new FieldGroup(
						new SliderField('BN', 'Brightness', -100, 100),
						new SliderField('R', 'R', 0, 255),
						new SliderField('G', 'G', 0, 255),
						new SliderField('B', 'B', 0, 255)
		);
		$CFGroup->setID('CFGroup');
		$CFGroup->setTitle('Custom Colorize');

thank.timo

If you're referring to the HTML ID attribute, then setAttribute('ID', 'CFGroup') is probably what you're after.

::create() isn't anything special over new (in terms of output) it simply returns a newly constructed object. The advantage is in dependency injection and that you can from chain it.

ie. new FormField()->setID() will give issues.
FormField::create()->setID() will be fine.

It's syntactic sugar for most people, until you start wanting to get a bit advanced with DI. It's recommended because without it there's no chance of DI in the future.

Hi Pyromanik
ive tested your suggestion but this also doesnt set an ID.
it would be handy to have an id on that field to use it in jquery.

class MyImageDecorator extends DataExtension :

function getCustomFields(){
		
		Requirements::javascript('mysite/javascript/ImageDecorator.js');
		Requirements::css("mysite/css/ImageDecorator.css");
		
		$previewSrc = $this->owner->getMyCMSFilter() ? $this->owner->GetMyCMSFilter()->SetHeight(100)->Link() : $this->owner->SetHeight(100)->Link();
		$size = $this->owner->getMyCMSFilter() ? $this->format_size(filesize($this->owner->GetMyCMSFilter()->getFullPath())) : $this->format_size(filesize($this->owner->getFullPath()));
		//$size = ceil(filesize($this->owner->GetMyCMSFilter()->getFullPath()) / 1024).' KB';
		$urlField = new FieldGroup( 
			new LiteralField('', '<div style="height: 100px;">
									<img id="loader" src="'.PROJECT_DIR.'/img/loading.gif"/>
									<img id="preview" style="display:none;" src="'.$previewSrc.'"/>
									</div>'
			),
			new LiteralField('',$size)
		);
		
		$urlField->setTitle('Preview');
		
		
		$selectionGroup = new OptionsetField(
					   $name = "Rotate",
					   $title = "Rotate",
					   $source = array(
						  "1" => "90º CW",
						  "2" => "90º CCW",
						  "3" => "180º"
					   ),
					   $value = ""
					);
		
		$filter = new OptionsetField(
					$name = "Filter",
					$title = "Filter",
					$source = array(
						"Colorize,100,10,10" => "Colorize Red",
						"Greyscale,0,0,255" => "Greyscale",
						"Colorize,10,100,10" => "Colorize Green",
						"Sepia" => "Sepia",
						"Colorize,10,10,100" => "Colorize Blue",
						"Custom" => "Custom Colorize",
						"" => "REMOVE FILTER"
					),
					$value = ""
		);
					
		$CFGroup = FieldGroup::create(
			new SliderField('BN', 'Brightness', -100, 100),
			new SliderField('R', 'Red', 0, 255),
			new SliderField('G', 'Green', 0, 255),
			new SliderField('B', 'Blue', 0, 255)
		)->setAttribute('ID', 'CFGroup');
		//$CFGroup->setID('CFGroup');
		//$CFGroup->setAttribute('ID', 'CFGroup');
		
					
		$fields = new FieldList();
		if($this->owner->getMyCMSFilter() || isset($_POST['Rotate'])){ 
			$fields->push($urlField);
		}
		$fields->push($selectionGroup);
		$fields->push($filter);
		$fields->push($CFGroup);
		
		
		return $fields;
    }

(function($) {
	$.entwine('ss',function($) {
		
		$('input[name=Filter]').entwine({  
		
			onmatch: function() {
				
				$active = $('input[name=Filter]:checked').val();
				$('#Filter').next().css({'display' : 'none'});  // ID ???? !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
				if($active == 'Custom'){
					$('#Filter').next().css( {'display' : 'block'} );
				}
			},
			onchange: function() {
				var radiovalue = $(this).val();
				if(radiovalue == 'Custom'){
					$('#Filter').next().css( {'display' : 'block'} );
				}else{
					$('#Filter').next().css( {'display' : 'none'} );
				}
			}
		});
	});
})(jQuery);

OK. Solved.

$CFGroup->setName('CFGroup');

sets an id.
is this documented anywhere? or am i too dumb?

timo.

The HTML id attribute is generated from the Field Name, yes.
Or more specifically a combination of the Form name (function that creates it/it submits to) and the Field name (FormField::create($name, $title, $value)).

So whatfor is : ->setID() ?
if it doesnt do what i exspect it does?

Nothing, looks like code rot from 2.4 days, when forms weren't nearly as flexible as they are now.
https://github.com/silverstripe/silverstripe-framework/blob/2.4/forms/CompositeField.php#L83
vs
https://github.com/silverstripe/silverstripe-framework/blob/3.1/templates/forms/CompositeField_holder.ss (furthermore this is why setAttribute() did nothing for you - CompositeField's template doesn't make use of attributes at all it seems, only $extraClass. setAttribute() is what you're after with most FormFields)

->setAttribute('ID', 'CFGroup');

also doesnt work
i really have hard times to read and undestand the api docs.