public static function isAjax() {
		if (isset ( $_SERVER ['HTTP_X_REQUESTED_WITH'] )) {
			if ('xmlhttprequest' == strtolower ( $_SERVER ['HTTP_X_REQUESTED_WITH'] ))
				return true;
		}
		//如果参数传递的参数中有ajax
		if (! empty ( $_POST ['ajax'] ) || ! empty ( $_GET ['ajax'] )) {
			return true;
		}
		return false;
	}