我正在尝试添加list table 到自定义管理页。我一直在跟踪this guide 和this reference implementation.

不幸的是，当我定义$this->items 要添加数据，nothing 显示在管理页面（甚至列表表周围的html）中，并且没有错误消息。如果我将该行注释掉（第行135), 然后，除了明显缺乏数据外，它还能工作。

我的代码：

<?php

add_action(\'admin_menu\', \'add_example_menues\');

function add_example_menues() {
    add_menu_page(\'test\', \'test\', \'administrator\', \'test-top\', \'build_test_page\');
    add_submenu_page(\'test-top\', \'All tests\', \'All tests\', \'administrator\', \'test-top\');
}

if(!class_exists(\'WP_List_Table\')){
    require_once( ABSPATH . \'wp-admin/includes/class-wp-list-table.php\' );
}

class test_List_Table extends WP_List_Table {
    function __construct() {
        parent::__construct( array(
            \'singular\' => \'test\',
            \'plural\' => \'tests\',
            \'ajax\' => false
        ));
    }


    function extra_tablenav ($which) {
        if ($which == "top") {
            echo "Top";
        }
        if ($which == "bottom") {
            echo "Bottom";
        }
    }

    function get_columns() {
        $columns = array(
            \'id\'    => \'ID\',
            \'title\'     => \'Title\',
            \'user_id\'   => \'User ID\',
            \'description\'   => \'Description\'
        );
        return $columns;
    }

    function get_sortable_columns() {
        return $sortable = array(
            \'id\'        => array(\'id\',false),
            \'title\'         => array(\'title\',false),
            \'user_id\'       => array(\'user_id\',false)
        );
    }

    function prepare_items() {
        global $wpdb;

        //data normally gotten from non-wp database. Wordpress db user has access, as per this SE post:
        //http://wordpress.stackexchange.com/questions/1604/using-wpdb-to-connect-to-a-separate-database
        $query = "SELECT `id`, `title`, `user_id`, `description` FROM otherdb.example_table";

        //pagination stuff
        $orderby = !empty($_GET["orderby"]) ? mysql_real_escape_string($_GET["orderby"]) : \'ASC\';
        $order = !empty($_GET["order"]) ? mysql_real_escape_string($_GET["order"]) : \'\';
        if(!empty($orderby) & !empty($order)){ $query.=\' ORDER BY \'.$orderby.\' \'.$order; }
        $totalitems = $wpdb->query($query);
        echo "$totalitems";
        $per_page = 5;
        $paged = !empty($_GET["paged"]) ? mysql_real_escape_string($_GET["paged"]) : \'\';
        if(empty($paged) || !is_numeric($paged) || $paged<=0 ){ $paged=1; }
        $totalpages = ceil($totalitems/$perpage);
        if(!empty($paged) && !empty($perpage)){
            $offset=($paged-1)*$perpage;
            $query.=\' LIMIT \'.(int)$offset.\',\'.(int)$perpage;
        }
        $this->set_pagination_args( array(
            "total_items" => 4,
            "total_pages" => 1,
            "per_page" => 5,
        ) );


        $columns = $this->get_columns();
        $hidden = array();
        $sortable = $this->get_sortable_columns();

        $this->_column_headers = array($columns, $hidden, $sortable);

        //actual data gotten from database, but for SE use hardcoded array
        //$data = $wpdb->get_results($query, ARRAY_N);

        $example_data = array(
                array(
                        \'id\'        => 1,
                        \'title\'     => \'nonsense\',
                        \'user_id\'    => 1,
                        \'description\'  => \'asdf\'
                ),
                array(
                        \'id\'        => 2,
                        \'title\'     => \'notanumber\',
                        \'user_id\'    => 2,
                        \'description\'  => \'404\'
                ),
                array(
                        \'id\'        => 3,
                        \'title\'     => \'I Am A Title\',
                        \'user_id\'    => 3,
                        \'description\'  => \'desc\'
                ),
                array(
                        \'id\'        => 4,
                        \'title\'     => \'Example\',
                        \'user_id\'    => 4,
                        \'description\'  => \'useless\'
                ),
                array(
                        \'id\'        => 5,
                        \'title\'     => \'aeou\',
                        \'user_id\'    => 5,
                        \'description\'  => \'keyboard layouts\'
                ),
                array(
                        \'id\'        => 6,
                        \'title\'     => \'example data\',
                        \'user_id\'    => 6,
                        \'description\'  => \'data example\'
                ),
                array(
                        \'id\'        => 7,
                        \'title\'     => \'last one\',
                        \'user_id\'       => 7,
                        \'description\'  => \'done\'
                )
            );


        //This is the line:
        $this->items = $example_data;
        //When the above line is commented, it works as expected (except for the lack of data, of course)
    }
}


function build_test_page() {

    $testListTable = new test_List_Table();
    $testListTable->prepare_items();

?>
<div class="wrap">

    <div id="icon-users" class="icon32"><br/></div>
    <h2>List Table Test</h2>

    <?php $testListTable->display() ?>

</div>
<?php
}
?>

我正在使用wordpress 4.1.1

这是怎么回事？为什么所有的东西都消失了，没有错误？