wp_dropdown_users( array|string $args = '' )

创建用户的下拉HTML内容。
Create dropdown HTML content of users.

说明（Description）

可以显示内容（默认情况下是这样），也可以通过设置“echo”参数来检索内容。不需要使用“include”和“exclude”参数；在这种情况下，将显示所有用户。只能使用一个“include”或“exclude”，但不能同时使用这两个。可用参数如下：

源码（Source）

/**
 * Create dropdown HTML content of users.
 *
 * The content can either be displayed, which it is by default or retrieved by
 * setting the 'echo' argument. The 'include' and 'exclude' arguments do not
 * need to be used; all users will be displayed in that case. Only one can be
 * used, either 'include' or 'exclude', but not both.
 *
 * The available arguments are as follows:
 *
 * @since 2.3.0
 *
 * @global wpdb $wpdb WordPress database object for queries.
 * @global int  $blog_id
 *
 * @param array|string $args {
 *     Optional. Array or string of arguments to generate a drop-down of users.
 *     {@see WP_User_Query::prepare_query() for additional available arguments.
 *
 *     @type string       $show_option_all         Text to show as the drop-down default (all).
 *                                                 Default empty.
 *     @type string       $show_option_none        Text to show as the drop-down default when no
 *                                                 users were found. Default empty.
 *     @type int|string   $option_none_value       Value to use for $show_option_non when no users
 *                                                 were found. Default -1.
 *     @type string       $hide_if_only_one_author Whether to skip generating the drop-down
 *                                                 if only one user was found. Default empty.
 *     @type string       $orderby                 Field to order found users by. Accepts user fields.
 *                                                 Default 'display_name'.
 *     @type string       $order                   Whether to order users in ascending or descending
 *                                                 order. Accepts 'ASC' (ascending) or 'DESC' (descending).
 *                                                 Default 'ASC'.
 *     @type array|string $include                 Array or comma-separated list of user IDs to include.
 *                                                 Default empty.
 *     @type array|string $exclude                 Array or comma-separated list of user IDs to exclude.
 *                                                 Default empty.
 *     @type bool|int     $multi                   Whether to skip the ID attribute on the 'select' element.
 *                                                 Accepts 1|true or 0|false. Default 0|false.
 *     @type string       $show                    User table column to display. If the selected item is empty
 *                                                 then the 'user_login' will be displayed in parentheses.
 *                                                 Accepts user fields. Default 'display_name'.
 *     @type int|bool     $echo                    Whether to echo or return the drop-down. Accepts 1|true (echo)
 *                                                 or 0|false (return). Default 1|true.
 *     @type int          $selected                Which user ID should be selected. Default 0.
 *     @type bool         $include_selected        Whether to always include the selected user ID in the drop-
 *                                                 down. Default false.
 *     @type string       $name                    Name attribute of select element. Default 'user'.
 *     @type string       $id                      ID attribute of the select element. Default is the value of $name.
 *     @type string       $class                   Class attribute of the select element. Default empty.
 *     @type int          $blog_id                 ID of blog (Multisite only). Default is ID of the current blog.
 *     @type string       $who                     Which type of users to query. Accepts only an empty string or
 *                                                 'authors'. Default empty.
 * }
 * @return string String of HTML content.
 */
function wp_dropdown_users( $args = '' ) {
	$defaults = array(
		'show_option_all' => '', 'show_option_none' => '', 'hide_if_only_one_author' => '',
		'orderby' => 'display_name', 'order' => 'ASC',
		'include' => '', 'exclude' => '', 'multi' => 0,
		'show' => 'display_name', 'echo' => 1,
		'selected' => 0, 'name' => 'user', 'class' => '', 'id' => '',
		'blog_id' => $GLOBALS['blog_id'], 'who' => '', 'include_selected' => false,
		'option_none_value' => -1
	);

	$defaults['selected'] = is_author() ? get_query_var( 'author' ) : 0;

	$r = wp_parse_args( $args, $defaults );
	$show = $r['show'];
	$show_option_all = $r['show_option_all'];
	$show_option_none = $r['show_option_none'];
	$option_none_value = $r['option_none_value'];

	$query_args = wp_array_slice_assoc( $r, array( 'blog_id', 'include', 'exclude', 'orderby', 'order', 'who' ) );
	$query_args['fields'] = array( 'ID', 'user_login', $show );
	$users = get_users( $query_args );

	$output = '';
	if ( ! empty( $users ) && ( empty( $r['hide_if_only_one_author'] ) || count( $users ) > 1 ) ) {
		$name = esc_attr( $r['name'] );
		if ( $r['multi'] && ! $r['id'] ) {
			$id = '';
		} else {
			$id = $r['id'] ? " id='" . esc_attr( $r['id'] ) . "'" : " id='$name'";
		}
		$output = "
";

		if ( $show_option_all ) {
			$output .= "	$show_option_all
";
		}

		if ( $show_option_none ) {
			$_selected = selected( $option_none_value, $r['selected'], false );
			$output .= "	$show_option_none
";
		}

		$found_selected = false;
		foreach ( (array) $users as $user ) {
			$user->ID = (int) $user->ID;
			$_selected = selected( $user->ID, $r['selected'], false );
			if ( $_selected ) {
				$found_selected = true;
			}
			$display = ! empty( $user->$show ) ? $user->$show : '('. $user->user_login . ')';
			$output .= "	" . esc_html( $display ) . "
";
		}

		if ( $r['include_selected'] && ! $found_selected && ( $r['selected'] > 0 ) ) {
			$user = get_userdata( $r['selected'] );
			$_selected = selected( $user->ID, $r['selected'], false );
			$display = ! empty( $user->$show ) ? $user->$show : '('. $user->user_login . ')';
			$output .= "	" . esc_html( $display ) . "
";
		}

		$output .= "";
	}

	/**
	 * Filter the wp_dropdown_users() HTML output.
	 *
	 * @since 2.3.0
	 *
	 * @param string $output HTML output generated by wp_dropdown_users().
	 */
	$html = apply_filters( 'wp_dropdown_users', $output );

	if ( $r['echo'] ) {
		echo $html;
	}
	return $html;
}

笔记（Notes）