get_avatar() 是 WordPress 默认获取的 Gravatar 头像的函数，函数通过用户 ID 或邮件地址获取用户头像，同时如果要正确显示头像需要将设置/讨论面板下的“显示头像”给勾选上。该函数的定义位于 wp-includes 文件夹下的 pluggable.php 中
相关代码如下：
if ( !function_exists( \'get_avatar\' ) ) :
/**
* Retrieve the avatar `<img>` tag for a user, email address, MD5 hash, comment, or post.
*
* @since 2.5.0
* @since 4.2.0 Optional `$args` parameter added.
*
* @param mixed $id_or_email The Gravatar to retrieve. Accepts a user_id, gravatar md5 hash,
* user email, WP_User object, WP_Post object, or WP_Comment object.
* @param int $size Optional. Height and width of the avatar image file in pixels. Default 96.
* @param string $default Optional. URL for the default image or a default type. Accepts \'404\'
* (return a 404 instead of a default image), \'retro\' (8bit), \'monsterid\'
* (monster), \'wavatar\' (cartoon face), \'indenticon\' (the \"quilt\"),
* \'mystery\', \'mm\', or \'mysteryman\' (The Oyster Man), \'blank\' (transparent GIF),
* or \'gravatar_default\' (the Gravatar logo). Default is the value of the
* \'avatar_default\' option, with a fallback of \'mystery\'.
* @param string $alt Optional. Alternative text to use in <img> tag. Default empty.
* @param array $args {
* Optional. Extra arguments to retrieve the avatar.
*
* @type int $height Display height of the avatar in pixels. Defaults to $size.
* @type int $width Display width of the avatar in pixels. Defaults to $size.
* @type bool $force_default Whether to always show the default image, never the Gravatar. Default false.
* @type string $rating What rating to display avatars up to. Accepts \'G\', \'PG\', \'R\', \'X\', and are
* judged in that order. Default is the value of the \'avatar_rating\' option.
* @type string $scheme URL scheme to use. See set_url_scheme() for accepted values.
* Default null.
* @type array|string $class Array or string of additional classes to add to the <img> element.
* Default null.
* @type bool $force_display Whether to always show the avatar - ignores the show_avatars option.
* Default false.
* @type string $extra_attr HTML attributes to insert in the IMG element. Is not sanitized. Default empty.
* }
* @return false|string `<img>` tag for the user\'s avatar. False on failure.
*/
function get_avatar( $id_or_email, $size = 96, $default = \'\', $alt = \'\', $args = null ) {
$defaults = array(
// get_avatar_data() args.
\'size\' => 96,
\'height\' => null,
\'width\' => null,
\'default\' => get_option( \'avatar_default\', \'mystery\' ),
\'force_default\' => false,
\'rating\' => get_option( \'avatar_rating\' ),
\'scheme\' => null,
\'alt\' => \'\',
\'class\' => null,
\'force_display\' => false,
\'extra_attr\' => \'\',
);
if ( empty( $args ) ) {
$args = array();
}
$args[\'size\'] = (int) $size;
$args[\'default\'] = $default;
$args[\'alt\'] = $alt;
$args = wp_parse_args( $args, $defaults );
if ( empty( $args[\'height\'] ) ) {
$args[\'height\'] = $args[\'size\'];
}
if ( empty( $args[\'width\'] ) ) {
$args[\'width\'] = $args[\'size\'];
}
if ( is_object( $id_or_email ) && isset( $id_or_email->comment_ID ) ) {
$id_or_email = get_comment( $id_or_email );
}
/**
* Filters whether to retrieve the avatar URL early.
*
* Passing a non-null value will effectively short-circuit get_avatar(), passing
* the value through the {@see \'get_avatar\'} filter and returning early.
*
* @since 4.2.0
*
* @param string $avatar HTML for the user\'s avatar. Default null.
* @param mixed $id_or_email The Gravatar to retrieve. Accepts a user_id, gravatar md5 hash,
* user email, WP_User object, WP_Post object, or WP_Comment object.
* @param array $args Arguments passed to get_avatar_url(), after processing.
*/
$avatar = apply_filters( \'pre_get_avatar\', null, $id_or_email, $args );
if ( ! is_null( $avatar ) ) {
/** This filter is documented in wp-includes/pluggable.php */
return apply_filters( \'get_avatar\', $avatar, $id_or_email, $args[\'size\'], $args[\'default\'], $args[\'alt\'], $args );
}
if ( ! $args[\'force_display\'] && ! get_option( \'show_avatars\' ) ) {
return false;
}
$url2x = get_avatar_url( $id_or_email, array_merge( $args, array( \'size\' => $args[\'size\'] * 2 ) ) );
$args = get_avatar_data( $id_or_email, $args );
$url = $args[\'url\'];
if ( ! $url || is_wp_error( $url ) ) {
return false;
}
$class = array( \'avatar\', \'avatar-\' . (int) $args[\'size\'], \'photo\' );
if ( ! $args[\'found_avatar\'] || $args[\'force_default\'] ) {
$class[] = \'avatar-default\';
}
if ( $args[\'class\'] ) {
if ( is_array( $args[\'class\'] ) ) {
$class = array_merge( $class, $args[\'class\'] );
} else {
$class[] = $args[\'class\'];
}
}
$avatar = sprintf(
\"<img alt=\'%s\' src=\'%s\' srcset=\'%s\' class=\'%s\' height=\'%d\' width=\'%d\' %s/>\",
esc_attr( $args[\'alt\'] ),
esc_url( $url ),
esc_url( $url2x ) . \' 2x\',
esc_attr( join( \' \', $class ) ),
(int) $args[\'height\'],
(int) $args[\'width\'],
$args[\'extra_attr\']
);
/**
* Filters the avatar to retrieve.
*
* @since 2.5.0
* @since 4.2.0 The `$args` parameter was added.
*
* @param string $avatar <img> tag for the user\'s avatar.
* @param mixed $id_or_email The Gravatar to retrieve. Accepts a user_id, gravatar md5 hash,
* user email, WP_User object, WP_Post object, or WP_Comment object.
* @param int $size Square avatar width and height in pixels to retrieve.
* @param string $default URL for the default image or a default type. Accepts \'404\', \'retro\', \'monsterid\',
* \'wavatar\', \'indenticon\',\'mystery\' (or \'mm\', or \'mysteryman\'), \'blank\', or \'gravatar_default\'.
* Default is the value of the \'avatar_default\' option, with a fallback of \'mystery\'.
* @param string $alt Alternative text to use in the avatar image tag. Default empty.
* @param array $args Arguments passed to get_avatar_data(), after processing.
*/
return apply_filters( \'get_avatar\', $avatar, $id_or_email, $args[\'size\'], $args[\'default\'], $args[\'alt\'], $args );
}
endif;
使用 get_avatar() 函数
对于 get_avatar() 函数的使用我们一般可以通过以下方式调用：
<?php echo get_avatar( $id_or_email, $size, $default, $alt, $args ); ?>$id_or_email：必填（整型/字符串/对象）。用户 ID 、邮件地址或者评论区评论对象。
$size：选填（整型）。要返回的 Gravatar 头像的大小，最大为 512 默认 96 。
$default：选填（字符串）。自定义的默认头像地址，默认“神秘人物”头像。
$alt：选填（字符串）。img 标签的 alt 属性值，图像的替换文本，默认为空。
$args：选填（数组）。设置新的参数以替换 get_avatar中 的默认参数。
$args 可设置的参数
如果要设置新的参数以替换 get_avatar中 的默认参数，必须在调用 get_avatar 之前声明新的参数，否则它们将不会生效。以下参数均为可选参数，由于使用较少，此处仅简单说下，具体内容请参阅文后官方文档！
size（整型、大小）、height（整型、高度）、width（整型、宽度）、default（字符串、默认头像）、force_default（布尔型、强制使用默认头像）、rating（字符串、头像等级 ‘G’, ‘PG’, ‘R’, ‘X’）、scheme（字符串，设置 URL 的 Scheme）、class（数组或字符串，设置 img 标签的 class 属性）、force_display（布尔型、是否强制显示 Gravatar 头像即使未勾选“显示头像”）、extra_attr（字符串，设置头像的 attributes 属性）。
官方文档：https://codex.wordpress.org/Function_Reference/get_avatar
