I always move my filters inside my query, this will inhibit them from showing anything when my query returns no results. You just need to move the following
echo $args[ 'before_widget' ];
if ( !empty( $title ) )
echo $args['before_title'] . $title . $args['after_title'];
to just after this line
if ( $related_posts ) { ?>
EDIT
I have quickly rewritten one of my widgets to accommodate my related posts function. I have commented a few places where there was issues. Hope this help
<?php
/**
* Related_Posts_Widget widget class
*
* Displays posts from a selected category
*
* @since 1.0.0
*/
class Related_Posts_Widget extends WP_Widget
{
public function __construct()
{
parent::__construct(
'widget_related_posts',
_x( 'Related Posts Widget', 'Related Posts Widget' ),
[ 'description' => __( 'Display a list of related posts.' ) ]
);
$this->alt_option_name="widget_related_posts";
add_action( 'save_post', [$this, 'flush_widget_cache'] );
add_action( 'deleted_post', [$this, 'flush_widget_cache'] );
add_action( 'switch_theme', [$this, 'flush_widget_cache'] );
}
public function widget( $args, $instance )
{
$cache = [];
if ( ! $this->is_preview() ) {
$cache = wp_cache_get( 'widget_rel_posts', 'widget' );
}
if ( ! is_array( $cache ) ) {
$cache = [];
}
if ( ! isset( $args['widget_id'] ) ) {
$args['widget_id'] = $this->id;
}
if ( isset( $cache[ $args['widget_id'] ] ) ) {
echo $cache[ $args['widget_id'] ];
return;
}
ob_start();
$title = ( ! empty( $instance['title'] ) ) ? $instance['title'] : __( 'Related Posts' );
/** This filter is documented in wp-includes/default-widgets.php */
$title = apply_filters( 'widget_title', $title, $instance, $this->id_base );
$number = ( ! empty( $instance['number'] ) ) ? absint( $instance['number'] ) : 5;
if ( ! $number ) {
$number = 5;
}
$cat_id = $instance['cat_id'];
$thumbnail = $instance['thumbnail'] ? true : false;
/**
* Filter the arguments for the Related Posts Widget.
*
* @since 1.0.0
*
*/
$cat_select = [
'numberposts' => $number,
'cat' => $cat,
];
if ( function_exists( 'get_related_posts' ) ) { // This line was wrong, get_related_posts_widget should be get_related_posts
$related_posts = get_related_posts( 'authors', $cat_select );
if ( $related_posts ) {
echo $args['before_widget'];
if ( $title ) { // This should not be !$title
echo $args['before_title'] . $title . $args['after_title'];
}
?>
<ul class="related-cat">
<?php foreach ( $related_posts as $post ) {
setup_postdata( $post ); ?>
<li>
<?php if ( $thumbnail ) : ?>
<figure class="post-thumbnail">
<?php the_post_thumbnail( 'tie-large' ); ?>
</figure>
<?php endif; ?>
<h3><a href="https://wordpress.stackexchange.com/questions/195844/<?php echo get_the_permalink( $post->ID ); ?>"> <?php echo get_the_title( $post->ID );?> </a></h3>
</li>
<?php } //foreach ( $related_posts as $post ) ?>
</ul>
<?php
} // end if
wp_reset_postdata(); // You forgot this, this is very very very important
echo $args['after_widget'];
}
if ( ! $this->is_preview() ) {
$cache[ $args['widget_id'] ] = ob_get_flush();
wp_cache_set( 'widget_rel_posts', $cache, 'widget' );
} else {
ob_end_flush();
}
}
public function update( $new_instance, $old_instance )
{
$instance = $old_instance;
$instance['title'] = strip_tags( $new_instance['title'] );
$instance['number'] = (int) $new_instance['number'];
$instance['cat_id'] = (int) $new_instance['cat_id'];
$instance['thumbnail'] = $new_instance['thumbnail'];
$this->flush_widget_cache();
$alloptions = wp_cache_get( 'alloptions', 'options' );
if ( isset($alloptions['widget_related_posts']) )
delete_option('widget_related_posts');
return $instance;
}
public function flush_widget_cache()
{
wp_cache_delete('widget_rel_posts', 'widget');
}
public function form( $instance )
{
$title = isset( $instance['title'] ) ? esc_attr( $instance['title'] ) : '';
$number = isset( $instance['number'] ) ? absint( $instance['number'] ) : 5;
$cat_id = isset( $instance['cat_id'] ) ? absint( $instance['cat_id'] ) : 1;
$thumbnail = isset( $instance['thumbnail'] ) ? $instance['thumbnail'] : false;
?>
<p>
<label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo $title; ?>" />
</p>
<p>
<label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of posts to show:' ); ?></label>
<input id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="text" value="<?php echo $number; ?>" size="3" />
</p>
<p>
<label for="<?php echo $this->get_field_id('cat_id'); ?>"><?php _e( 'Category Name:' )?></label>
<select id="<?php echo $this->get_field_id('cat_id'); ?>" name="<?php echo $this->get_field_name('cat_id'); ?>">
<?php
$this->categories = get_categories();
foreach ( $this->categories as $cat ) {
$selected = ( $cat->term_id == esc_attr( $cat_id ) ) ? ' selected = "selected" ' : '';
$option = '<option '.$selected .'value="' . $cat->term_id;
$option = $option .'">';
$option = $option .$cat->name;
$option = $option .'</option>';
echo $option;
}
?>
</select>
</p>
<p>
<label for="<?php echo $this->get_field_id('thumbnail'); ?>"><?php _e( 'Hide post thumbnail' ); ?></label>
<?php $checked = ( $thumbnail ) ? ' checked=\"checked\" ' : ''; ?>
<input type="checkbox" id="<?php echo $this->get_field_id( 'thumbnail' ); ?>" name="<?php echo $this->get_field_name( 'thumbnail' ); ?>" value="true" <?php echo $checked; ?> />
</p>
<?php
}
}
add_action( 'widgets_init', function ()
{
register_widget( 'Related_Posts_Widget' );
});