WP Widget Inheritance

class-bs-recent-category-posts.php

<?php
/**
 * Created by PhpStorm.
 * User: rumur
 * Date: 11/10/16
 * Time: 13:13
 */

class BS_Recent_Category_Posts extends WP_Widget_Recent_Posts {

	protected $textdomain = 'bs';
	protected $class_prefix = 'bs_';
	protected $cat = 0;

	function __construct() {
		$this->textdomain = defined( 'BS_TEXT_DOMAIN' ) ? BS_TEXT_DOMAIN : $this->textdomain;
		$widget_ops = array(
			'classname' => $this->prep_class( 'widget_recent_category_entries' ),
			'description' => __( 'The most recent posts from specific category on your site.', $this->textdomain ),
			'customize_selective_refresh' => true,
		);
		WP_Widget::__construct( 'bs-recent-posts', __( 'Recent Category Posts', $this->textdomain ), $widget_ops );
	}

	protected function prep_class( $class ) {
		return $this->class_prefix . $class;
	}

	public function extends_widget_posts_args( $args ) {
		$args['cat'] = $this->cat;
		return $args;
	}

	public function update( $new_instance, $old_instance ) {
		$instance = parent::update( $new_instance, $old_instance );
		$instance['cat'] = (int) $new_instance['cat'];

		return $instance;
	}

	public function form( $instance ) {
		$cat = isset( $instance['cat'] ) ? $instance['cat'] : 0;
		parent::form( $instance );
		?>
		<p>
			<label>
				<?php _e( 'Category', $this->textdomain ); ?>:
				<?php wp_dropdown_categories( array(
					'name'     => $this->get_field_name( 'cat' ),
					'selected' => $cat
				) ); ?>
			</label>
		</p>
		<?php
	}

	public function widget( $args, $instance ) {
		$this->cat = $instance['cat'];
		add_filter( 'widget_posts_args', array( $this, 'extends_widget_posts_args' ) );
		unset( $instance['cat'] );
		parent::widget( $args, $instance );
		remove_filter( 'widget_posts_args', array( $this, 'extends_widget_posts_args' ) );
	}
}

add_action( 'widgets_init', function() {
	register_widget( 'BS_Recent_Category_Posts' );
});