我正在为广告商的show name创建一个WordPress小部件。

当我尝试激活插件时，出现了一个错误

The plugin generated 3 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.

1-删除PHP打开或关闭标记前后的空白

2-将编码更改为UTF8-BOM

<?php
class adsMain extends WP_Widget {

    public function __construct() {

        parent::__construct(
            \'adsMain\',
            __( \'تبلیغات\', \'text\' ),
            array(
                \'classname\'   => \'adsMain\',
                \'description\' => __( \'برای ایجاد تبلیغات جدید این کادر را به مکان دلخواه خود بکشید.\', \'text\' )
            )
        ); 
    }
    /**  
     * Front-end display of widget.
     *
     * @see WP_Widget::widget()
     *
     * @param array $args     Widget arguments.
     * @param array $instance Saved values from database.
     */
    public function widget( $args, $instance ) {

        extract( $args );

        $advertiser = apply_filters( \'widget_title\', $instance[\'advertiser\'] );

        echo $advertiser;

    }

    /**
      * Sanitize widget form values as they are saved.
      *
      * @see WP_Widget::update()
      *
      * @param array $new_instance Values just sent to be saved.
      * @param array $old_instance Previously saved values from database.
      *
      * @return array Updated safe values to be saved.
      */
    public function update( $new_instance, $old_instance ) {

        $instance = $old_instance;

        $instance[\'advertiser\'] = strip_tags( $new_instance[\'advertiser\'] );

        return $instance;

    }

    /**
      * Back-end widget form.
      *
      * @see WP_Widget::form()
      *
      * @param array $instance Previously saved values from database.
      */
    public function form( $instance ) {

        $advertiser = ( isset($instance[\'advertiser\']) ? esc_attr ( $instance[\'advertiser\'] ) : \'\' );
?>

        <p>
            <label for="<?php echo $this->get_field_id(\'advertiser\'); ?>"><?php _e(\'نام شخص / شرکت تبلیغ دهنده:\'); ?></label>
            <input class="widefat" id="<?php echo $this->get_field_id(\'advertiser\'); ?>" name="<?php echo $this->get_field_name(\'advertiser\'); ?>" type="text" value="<?php echo $advertiser; ?>" />
        </p>
<?php
    }

}

/* Register uploader */
add_action (\'admin_enqueue_scripts\', function () {
    wp_register_script(\'adsMain-script\' , plugins_url( \'/js/adsMain-script.js\', __FILE__ ), array( \'jquery\' ), \'20160904\', true );
    wp_enqueue_script(\'adsMain-script\');
    wp_enqueue_media();
});

/* Register the widget */
add_action(\'widgets_init\', function() {
     register_widget( \'adsMain\' );
});
?>