我想向媒体上载程序添加自定义图像大小：

为了做到这一点，我使用以下代码（为了方便起见，这里有注释）：

// this function adds the custom image sizes to the media uploader
function my_insert_custom_image_sizes( $sizes ) {
    // get the custom image sizes
    global $_wp_additional_image_sizes;
    // if there are none, just return the built-in sizes
    if ( empty( $_wp_additional_image_sizes ) )
        return $sizes;

    // add all the custom sizes to the built-in sizes
    foreach ( $_wp_additional_image_sizes as $id => $data ) {
        // take the size ID (e.g., \'my-name\'), replace hyphens with spaces,
        // and capitalise the first letter of each word
        if ( !isset($sizes[$id]) )
            $sizes[$id] = ucfirst( str_replace( \'-\', \' \', $id ) );
    }

    return $sizes;
}

// define the init function next, which sets up all the necessary stuff
function custom_image_setup () {
    add_theme_support( \'post-thumbnails\' );
    add_image_size( \'my-size1\', 250, 250 );
    add_image_size( \'my-size2\', 350, 350 );
    add_image_size( \'my-size3\', 450, 450 );
    add_filter( \'image_size_names_choose\', \'my_insert_custom_image_sizes\' );
}

// attach that init function to the \'after_setup_theme\' hook
// so it runs on each page load once your theme\'s been loaded
add_action( \'after_setup_theme\', \'custom_image_setup\' );

此代码工作正常。还有一个问题：上载图像时，如果图像小于最小自定义图像大小的尺寸，则会出现以下错误：Invalid argument supplied for foreach().

我想问题来自my_insert_custom_image_sizes 作用因此，基本上，当没有生成自定义图像时，会出现错误。我怎样才能解决这个问题？我有一种感觉，问题很简单，我忽略了，但我迷路了。。。

如果要复制此错误，只需将上述代码粘贴到函数中，然后上载一个smaller 大于250x250像素。

UPDATE: 经过进一步研究，该错误似乎与我的JPEG压缩函数中的foreach有关：

// Set JPEG compression quality
add_filter(\'jpeg_quality\', create_function(\'$quality\', \'return 100;\'));
add_action(\'added_post_meta\', \'ad_update_jpeg_quality\', 10, 4);

function ad_update_jpeg_quality($meta_id, $attach_id, $meta_key, $attach_meta) {

    if ($meta_key == \'_wp_attachment_metadata\') {

        $post = get_post($attach_id);

        if ($post->post_mime_type == \'image/jpeg\') {

            $pathinfo = pathinfo($attach_meta[\'file\']);
            $uploads = wp_upload_dir();
            $dir = $uploads[\'basedir\'] . \'/\' . $pathinfo[\'dirname\'];

            foreach ($attach_meta[\'sizes\'] as $size => $value) {

                $image = $dir . \'/\' . $value[\'file\'];
                $resource = imagecreatefromjpeg($image);

                if ($size == \'large\') {
                    // set the jpeg quality for \'large\' size
                    imagejpeg($resource, $image, 35);
                } elseif ($size == \'medium\') {
                    // set the jpeg quality for the \'medium\' size
                    imagejpeg($resource, $image, 35);
                } elseif ($size == \'small\') {
                    // set the jpeg quality for the \'small\' size
                    imagejpeg($resource, $image, 40);
                } else {
                    // set the jpeg quality for the rest of sizes
                    imagejpeg($resource, $image, 90);
                }

                imagedestroy($resource);
            }
        }
    }
}

有什么想法吗？有什么问题吗？

foreach ( (array) $attach_meta[\'sizes\'] as $size => $value ) {