class-mk-courses-widget.php

<?php

/**
 * A widget that lists all the Courses.
 */
class MK_Courses_Widget extends WP_Widget {

	/**
	 * Sets up the widgets name etc
	 */
	public function __construct() {
		$widget_ops = array( 
			'classname' => 'mk_courses_widget',
			'description' => 'A list of all Courses by Subject',
		);
		parent::__construct( 'mk_courses_widget', 'Courses Widget', $widget_ops );
	}

	/**
	 * Outputs the content of the widget
	 *
	 * @param array $args
	 * @param array $instance
	 */
	public function widget( $args, $instance ) {
		$courses = get_posts( [
			'post_type' => MK_Courses::POST_TYPE,
			'posts_per_page' => -1,
			'post_status' => 'publish',
			'orderby' => 'title',
			'order' => 'ASC',
		] );

		echo $args['before_widget'];
		if ( ! empty( $instance['title'] ) ) {
			echo $args['before_title'] . apply_filters( 'widget_title', $instance['title'] ) . $args['after_title'];
		}
		?>
		<ul>
			<?php foreach ( $courses as $course ): ?>
				<li><a href="<?php the_permalink( $course->ID ) ?>"><?php echo esc_html( $course->post_title ) ?></a></li>
			<?php endforeach ?>
		</ul>
		<?php
		echo $args['after_widget'];
	}

	/**
	 * Outputs the options form on admin
	 *
	 * @param array $instance The widget options
	 */
	public function form( $instance ) {
		$title = ! empty( $instance['title'] ) ? $instance['title'] : esc_html__( 'Courses', 'text_domain' );
		?>
		<p>
			<label for="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>"><?php esc_attr_e( 'Title:', 'text_domain' ); ?></label> 
			<input class="widefat" id="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>" name="<?php echo esc_attr( $this->get_field_name( 'title' ) ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>">
		</p>
		<?php 
	}

	/**
	 * Processing widget options on save
	 *
	 * @param array $new_instance The new options
	 * @param array $old_instance The previous options
	 *
	 * @return array
	 */
	public function update( $new_instance, $old_instance ) {
		$instance = array();
		$instance['title'] = ( ! empty( $new_instance['title'] ) ) ? strip_tags( $new_instance['title'] ) : '';

		return $instance;
	}
}

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