wordpress - 如何在自定义walker中返回页面id

Question

我正在尝试使用自定义步行器来使用自定义导航菜单项返回页面缩略图。我的完整walker在下面，看来这一段

$thumbnail = '';
if( $id = has_post_thumbnail( (int)$item->object_id ) ) {
$thumbnail = get_the_post_thumbnail( $id );
}

没有提取页面ID，所以我没有得到缩略图。感谢任何帮助

/*
* Create HTML list of nav menu items.
* Replacement for the native Walker, using the description.
*
* @see    http://wordpress.stackexchange.com/q/14037/
* @author toscho, http://toscho.de
*/
class Thumbnail_Walker extends Walker_Nav_Menu
{
/**
* Start the element output.
*
* @param  string $output Passed by reference. Used to append additional content.
* @param  object $item   Menu item data object.
* @param  int $depth     Depth of menu item. May be used for padding.
* @param  array $args    Additional strings.
* @return void
*/
function start_el(&$output, $item, $depth, $args)
{
$classes     = empty ( $item->classes ) ? array () : (array) $item->classes;

$class_names = join(
    ' '
,   apply_filters(
        'nav_menu_css_class'
    ,   array_filter( $classes ), $item
    )
);

! empty ( $class_names )
    and $class_names = ' class="'. esc_attr( $class_names ) . '"';

$output .= "<li id='menu-item-$item->ID' $class_names>";

$attributes  = '';

! empty( $item->attr_title )
    and $attributes .= ' title="'  . esc_attr( $item->attr_title ) .'"';
! empty( $item->target )
    and $attributes .= ' target="' . esc_attr( $item->target     ) .'"';
! empty( $item->xfn )
    and $attributes .= ' rel="'    . esc_attr( $item->xfn        ) .'"';
! empty( $item->url )
    and $attributes .= ' href="'   . esc_attr( $item->url        ) .'"';

// insert thumbnail
// you may change this
$thumbnail = '';
if( $id = has_post_thumbnail( (int)$item->object_id ) ) {
    $thumbnail = get_the_post_thumbnail( $id );
}

$title = apply_filters( 'the_title', $item->title, $item->ID );

$item_output = $args->before
    . "<a $attributes>"
    . $args->link_before
    . $title
    . '</a> '
    . $args->link_after
    . $thumbnail
    . $args->after;

// Since $output is called by reference we don't need to return anything.
$output .= apply_filters(
    'walker_nav_menu_start_el'
,   $item_output
,   $item
,   $depth
,   $args
);
}
}

Answer 1

根据http://phpdoc.wordpress.org 看起来您可以将 $id 参数添加到 $args 之后的 start_el 函数中，如下所示:

function start_el(&$output, $item, $depth, $args, $id)