Site-Specific WordPress Plugin Template (widgets)

plugin-template(widget).php

<?php
/*
Plugin Name: Template Site Plugin for example.com
Description: Site specific plugin template for example.com, in this case we are creating a widget
*/
////////////////////////////////////////////
// Start Adding Functions Below this Line //
////////////////////////////////////////////

// Create a widget
class prefixname_widget extends WP_Widget {

  function __construct() {
    parent::__construct(
      // Base ID of the widget
      'prefixname_widget',

      // Widget name will appear in UI
      __('Widget Name', 'prefixname_widget_domain'),

      // Widget description
      array( 'description' => __( 'Sample widget', 'prefixname_widget_domain' ), )
    );
  }

  // Creating widget front-end
  // This is where the action happens
  public function widget( $args, $instance ) {
    $title = apply_filters( 'widget_title', $instance['title'] );
    // before and after widget arguments are defined by themes
    echo $args['before_widget'];
    if ( ! empty( $title ) )
    echo $args['before_title'] . $title . $args['after_title'];

    // This is where you run the code and display the output
    echo __( 'Hello, World!', 'prefixname_widget_domain' );
    echo $args['after_widget'];
  }

  // Widget Backend
  public function form( $instance ) {
    if ( isset( $instance[ 'title' ] ) ) {
      $title = $instance[ 'title' ];
    }
    else {
      $title = __( 'New title', 'prefixname_widget_domain' );
    }
    // Widget admin form
  ?>
    <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 esc_attr( $title ); ?>" />
    </p>
  <?php
  }

  // Updating widget replacing old instances with new
  public function update( $new_instance, $old_instance ) {
  $instance = array();
  $instance['title'] = ( ! empty( $new_instance['title'] ) ) ? strip_tags( $new_instance['title'] ) : '';
    return $instance;
  }
}

// Register and load the widget
function prefixname_load_widget() {
  register_widget( 'prefixname_widget' );
}
add_action( 'widgets_init', 'prefixname_load_widget' );

///////////////////////////////////////////
// Stop adding functions below this line //
///////////////////////////////////////////
?>