显示从GCM发送的多行通知

我正在使用下面的PHP函数向android设备发送通知。我收到一行通知。如果有更多内容，我如何将其修改为多行。安卓应用程序中没有通知布局或任何内容。

public function send_notification($registatoin_ids, $message) {
    // Set POST variables
    $url = 'https://android.googleapis.com/gcm/send';
    $fields = array(
        'registration_ids' => $registatoin_ids,
        'data' => $message,
    );
    $headers = array(
        'Authorization: key=' . GOOGLE_API_KEY,
        'Content-Type: application/json'
    );
    // Open connection
    $ch = curl_init();
    // Set the url, number of POST vars, POST data
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    // Disabling SSL Certificate support temporarly
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
    // Execute post
    $result = curl_exec($ch);
    if ($result === FALSE) {
        die('Curl failed: ' . curl_error($ch));
    }
    // Close connection
    curl_close($ch);
    echo $result;
}