plugin development - How does update method in Widget class saves $instance array from Select tag?

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Following a tutorial and it works fine. I just can't understand how update method saves $instance array in the database from Select tag? You can choose default or full, slick save in the admin area and it saves in the db.

   public function widget( $args, $instance ) {
      echo $args['before_widget'];

          echo '<div class="g-ytsubscribe"       
              data-layout="'.$instance['data_layout'].'" 
              data-count="default">
            </div>';
      
      echo $args['after_widget'];
    }

    public function form( $instance ) {
      $data_layout = ! empty( $instance['data_layout'] ) ? $instance['data_layout'] : esc_html__( 'default', 'yts_domain' );
      ?>
      
      
      <select class="widefat" 
        <option value="default" <?php echo ($data_layout == 'default' ? 'selected' : ''); ?>>Default</option>
        <option value="full" <?php echo ($data_layout == 'full' ? 'selected' : ''); ?>>Full</option>
      </select>
      
      }
      
    public function update( $new_instance, $old_instance ) {
      $instance = array();

      $instance['data_layout'] = ( ! empty( $new_instance['data_layout'] ) ) ? sanitize_text_field( $new_instance['data_layout'] ) : '';

      return $instance;
    }

Following a tutorial and it works fine. I just can't understand how update method saves $instance array in the database from Select tag? You can choose default or full, slick save in the admin area and it saves in the db.

   public function widget( $args, $instance ) {
      echo $args['before_widget'];

          echo '<div class="g-ytsubscribe"       
              data-layout="'.$instance['data_layout'].'" 
              data-count="default">
            </div>';
      
      echo $args['after_widget'];
    }

    public function form( $instance ) {
      $data_layout = ! empty( $instance['data_layout'] ) ? $instance['data_layout'] : esc_html__( 'default', 'yts_domain' );
      ?>
      
      
      <select class="widefat" 
        <option value="default" <?php echo ($data_layout == 'default' ? 'selected' : ''); ?>>Default</option>
        <option value="full" <?php echo ($data_layout == 'full' ? 'selected' : ''); ?>>Full</option>
      </select>
      
      }
      
    public function update( $new_instance, $old_instance ) {
      $instance = array();

      $instance['data_layout'] = ( ! empty( $new_instance['data_layout'] ) ) ? sanitize_text_field( $new_instance['data_layout'] ) : '';

      return $instance;
    }

• plugin-development
• widgets

Share Improve this question edited May 12, 2021 at 18:08 Marina Dunst asked May 11, 2021 at 20:14 Marina DunstMarina Dunst 15955 bronze badges 1

• So my guess is that it looks at the form and collects values using their Ids. For example I have an input field and select field. It looks at whatever values are present at the time when you click Save, updates $instance array and calls update with new and old data. – Marina Dunst Commented May 12, 2021 at 18:38

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1 Answer 1

Sorted by: Reset to default 0

When you create a widget you're extending the WP_Widget class:

class Foo_Widget extends WP_Widget {

The actual saving of the values in the database is handled by the parent class, in the update_callback() method.

So all your widget needs to do is tell it the new values, which you do by defining the update() method.

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