public function getActivitiesByChannelId($channelId)
{
if (empty($channelId)) {
throw new \InvalidArgumentException('ChannelId must be supplied');
}
$API_URL = $this->getApi('activities');
$params = array('channelId' => $channelId, 'part' => 'id, snippet, contentDetails');
$apiData = $this->api_get($API_URL, $params);
return $this->decodeList($apiData);
}