praiadeseselle/wire/modules/Inputfield/InputfieldSelectMultiple.module

<?php namespace ProcessWire;

/**
 * Select Multiple Inputfield
 * 
 * An Inputfield for handling multiple selection using HTML `<select multiple>`.
 * Also a base type for other multiple selection types (checkboxes, asmSelect, etc.)
 * 
 * ProcessWire 3.x, Copyright 2022 by Ryan Cramer
 * https://processwire.com
 *
 * @property int $size
 * 
 */

class InputfieldSelectMultiple extends InputfieldSelect implements InputfieldHasArrayValue {

	/**
	 * Default 'size' attribute value
	 * 
	 */
	const defaultSize = 10;

	/**
	 * Get module info
	 * 
	 * @return array
	 * 
	 */
	public static function getModuleInfo() {
		return array(
			'title' => __('Select Multiple', __FILE__), // Module Title
			'summary' => __('Select multiple items from a list', __FILE__), // Module Summary
			'version' => 101,
			'permanent' => true, 
		);
	}

	/**
	 * Construct
	 * 
	 */
	public function __construct() {
		parent::__construct();
		$this->setAttribute('multiple', 'multiple'); 
		$this->setAttribute('size', self::defaultSize); 
	}

	/**
	 * Add options only if they are non-blank
	 *
	 * We don't need blank options in a select multiple since the unselected state involves no selected options
	 * 
	 * @param string|int $value
	 * @param string|null $label
	 * @param array|null $attributes
	 * @return InputfieldSelect|InputfieldSelectMultiple|self
	 *
	 */
	public function addOption($value, $label = null, array $attributes = null) {
		if(is_null($value) || (is_string($value) && !strlen($value))) return $this; 
		return parent::addOption($value, $label, $attributes); 
	}

	/**
	 * Configure Inputfield
	 * 
	 * @return InputfieldWrapper
	 * 
	 */
	public function ___getConfigInputfields() {
		$inputfields = parent::___getConfigInputfields();	
		if($this->className() === 'InputfieldSelectMultiple') {
			// descending classes may null out the 'size' attribute if they don't need it
			/** @var InputfieldInteger $f */
			$f = $this->wire()->modules->get('InputfieldInteger'); 
			$f->label = $this->_('Size: number of rows visible at once in the select multiple'); 
			$f->attr('name', 'size'); 
			$f->attr('value', (int) $this->attr('size')); 
			$inputfields->add($f);
		}
		return $inputfields; 
	}
}