实时从数据阅读器终端获取数据到 GUI

Question

我有一个数据读取器，它从缓冲区获取数据并将输出显示到控制台。现在我想将数据实时查看到文本编辑中。 我已经看到了一些示例，展示了如何从文本文件中读取数据（非实时）。

请查找附件。

/* Create a DataReader for the chatMessageTopic Topic (using the appropriate QoS). */
parentReader = chatSubscriber->create_datareader(
    chatMessageTopic.in(),
    DATAREADER_QOS_USE_TOPIC_QOS,
    NULL,
    STATUS_MASK_NONE);
checkHandle(parentReader.in(), "DDS::Subscriber::create_datareader");

/* Narrow the abstract parent into its typed representative. */
chatAdmin = Chat::ChatMessageDataReader::_narrow(parentReader.in());
checkHandle(chatAdmin.in(), "Chat::ChatMessageDataReader::_narrow");

/* Print a message that the MessageBoard has opened. */
cout << "MessageBoard has opened: send ChatMessages...." << endl << endl;

while (!terminated) {
    /* Note: using read does not remove the samples from
       unregistered instances from the DataReader. This means
       that the DataRase would use more and more resources.
       That's why we use take here instead. */

    status = chatAdmin->take(
        msgSeq,
        infoSeq,
        LENGTH_UNLIMITED,
        ANY_SAMPLE_STATE,
        ANY_VIEW_STATE,
        ALIVE_INSTANCE_STATE );
    checkStatus(status, "Chat::ChatMessageDataReader::take");

    for (DDS::ULong i = 0; i < msgSeq->length(); i++) {
       ChatMessage *msg = &(msgSeq[i]);
       cout << msg->index << ": " << msg->content << endl;
       fflush(stdout);
    }

    status = chatAdmin->return_loan(msgSeq, infoSeq);
    checkStatus(status, "Chat::ChatMessageDataReader::return_loan");

Answer 1

您可能不希望您的 UI 以 1000Hz 的频率刷新。因此，在繁忙的循环中运行此代码是没有意义的。相反，以合理的刷新率运行它，例如30Hz，来自计时器。

出于性能原因，发出批处理以及日志的单个行可能会有所帮助：

让我们抽象一下：

class DDSProcessor : public QObject {
  Q_OBJECT
  QBasicTimer m_timer;
  DDS::Subscriber * m_chatSubscriber;
  Chat::ChatMessageDataReader * m_chatDataReader = nullptr;
  ...
  Q_SIGNAL void message(const QString &);
  Q_SIGNAL void messages(const QStringList &);
  void timerEvent(QTimerEvent * ev) {
    if (ev->timerId() != m_timer.timerId()) return;
    auto status = chatAdmin->take(
        msgSeq,
        infoSeq,
        LENGTH_UNLIMITED,
        ANY_SAMPLE_STATE,
        ANY_VIEW_STATE,
        ALIVE_INSTANCE_STATE );
    checkStatus(status, "Chat::ChatMessageDataReader::take");
    QStringList texts;
    for (DDS::ULong i = 0; i < msgSeq->length(); i++) {
       auto msg = &(msgSeq[i]);
       auto text = tr("%1: %2").arg(msg->index).arg(msg->content);
       texts << text;
       emit message(text);
    }
    emit messages(texts);
    status = chatAdmin->return_loan(msgSeq, infoSeq);
    checkStatus(status, "Chat::ChatMessageDataReader::return_loan");
  }
public:
  void start() {
    auto reader = m_chatSubscriber->create_datareader(
      m_chatMessageTopic.in(), ...);
    checkHandle(read.in(), "DDS::Subscriber::create_datareader");
    m_chatDataReader = Chat::ChatMessageDataReader::_narrow(reader.in());
    checkHandler(m_chatDataReader.in(), "Chat::ChatMessageDataReader::_narrow");
    auto text = tr("MessageBoard had opened: send ChatMessages.");
    emit message(text);
    emit messages(text);
    m_timer.start(this, 1000/30);
  }
  ...
};

我对 DDS 库不够熟悉，但是您应该使用一些回调来获得通知，然后您会从回调中发出信号。这将消除对显式 UI 更新循环的需要。

那么，您在 UI 中所要做的就是对 DDSProcessor 发出的消息采取行动：

void setup(DDSProcessor * src, QTextEdit * dst) {
  connect(src, &DDSProcessor::message, dst, &QTextEdit::append);
}

请注意，QTextEdit 和 QPlainTextEdit 都非常慢，不适合快速记录。最简单的解决方法是使用带有QListView 的列表模型，并利用批处理日志条目信号：

int main(int argc, char ** argv) {
  QApplication app(argc, argv);
  QStringListModel logModel;
  QListView view;
  DDSProcessor processor;
  QObject::connect(&processor, &DDSProcessor::messages, &logModel, [&](const QStringList & texts){
    auto row = logModel.rowCount();
    logModel.insertRows(row, texts.count());
    for (auto const & text : texts)
      logModel.setData(model.index(row++), text);
  });
  view.setModel(&logModel);
  view.show();
  view.setUniformItemSizes(true); // needed for performance
  ...
  return app.exec();
}

Answer 2

这是一个同步记录到 GUI 的最小示例：

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);
  QPlainTextEdit edit;
  edit.show();
  int x = 0;
  while (edit.isVisible()) {
    x++;
    edit.appendPlainText(QString("test %1").arg(x));
    qApp->processEvents();
  }
  return 0;
}