我有AJAX图像上传功能attachment_id 价值我想将其保存为全局变量，并在不同的函数中使用它，该函数用于设置存在后缩略图时的状态。

这就是我到目前为止所做的，但没有工作。

Image upload

function write_here_featured_image_upload() {
    //var_dump($_FILES);

    // Temporary post id
    $post_id = 0;

    // These files need to be included as dependencies when on the front end.
    require_once( ABSPATH . \'wp-admin/includes/image.php\' );
    require_once( ABSPATH . \'wp-admin/includes/file.php\' );
    require_once( ABSPATH . \'wp-admin/includes/media.php\' );

    // Let WordPress handle the upload.
    global $attachment_id;
    $attachment_id = media_handle_upload(\'file\' , $post_id );
    $image_attributes = wp_get_attachment_image_src( $attachment_id, \'thumbnail\' );

    echo $image_attributes[0];

    die();
}
add_action( \'wp_ajax_write_here_img_upload\', \'write_here_featured_image_upload\' );

Add post function

function write_here_add_new_post() {
    $post_id = wp_insert_post($new_post);
    //echo "Post Added ".$post_id;

    if(isset($attachment_id)){
        set_post_thumbnail( $post_id, $attachment_id );
    }
}