如何在Android MQTT中使用DisconnectedBufferOptions.setDeleteOldestMessages？

Question

这与Android的paho MQTT客户端有关：lazy var searchBar = UISearchBar(frame: CGRect.zero) override func viewDidLoad() { tableView.delegate = self tableView.dataSource = self searchBar.searchBarStyle = .minimal navigationItem.titleView = searchBar } 的Javadoc未指定DisconnectedBufferOptions的确切行为。如果我将其设置为setDeleteOldestMessages()，并且消息数量超出缓冲区的容纳范围，结果将是什么？

Answer 1

看看Paho source code：

/**
 * This will add a new message to the offline buffer,
 * if the buffer is full and deleteOldestMessages is enabled
 * then the 0th item in the buffer will be deleted and the
 * new message will be added. If it is not enabled then an
 * MqttException will be thrown.
 * @param message the {@link MqttWireMessage} that will be buffered
 * @param token the associated {@link MqttToken}
 * @throws MqttException if the Buffer is full
 */
public void putMessage(MqttWireMessage message, MqttToken token) throws MqttException{
    BufferedMessage bufferedMessage = new BufferedMessage(message, token);
    synchronized (bufLock) {
        if(buffer.size() < bufferOpts.getBufferSize()){
            buffer.add(bufferedMessage);
        } else if(bufferOpts.isDeleteOldestMessages() == true){
            buffer.remove(0);
            buffer.add(bufferedMessage);
        }else {
            throw new MqttException(MqttException.REASON_CODE_DISCONNECTED_BUFFER_FULL);
        }
    }
}