如何从线程的结果返回Qt对象(Qtfutur)

Question

我正在尝试从服务器加载一些数据并填写Qt列表。 我想在一个线程中运行 dowloanding。 所以有以下代码：

• 应用程序中的主要功能.cpp

  loadInterestPlaces(QString& urlInterestPlaces) {
  LoadData* Data = new LoadData(urlInterestPlaces);
  QFuture< list <InterestPlace *> > future = QtConcurrent::run(Data,
          &LoadData::startLoading);
  
  // Invoke our onLoadingFinished slot after the loading has finished.
  bool ok = connect(&m_watcher, SIGNAL(finished()), this,
          SLOT(onLoadingFinished()));
  Q_ASSERT(ok);
  Q_UNUSED(ok);
  // starts watching the given future
  m_watcher.setFuture(future);
  }
  void ApplicationUI::onLoadingFinished() {
  qDebug() << "Loading finished";
  
  interestPlacesList = m_watcher.future().result();
  qDebug() << "List size= " << interestPlacesList.size();
      }
          }
  

• 加载数据.cpp文件：这是启动借出函数的代码：

  std::list<InterestPlace *> LoadData::startLoading()
  {
  QNetworkAccessManager* netManager = new QNetworkAccessManager(this);
  const QUrl url(_URL);
  QNetworkRequest request(url);
  QNetworkReply* reply = netManager->get(request);
  netManager->moveToThread(this->thread());
  netManager->setParent(this);
  bool ok = connect(reply, SIGNAL(finished()), this, SLOT(onReplyFinished()));
  qDebug() << reply->isFinished();
  Q_ASSERT(ok);
  Q_UNUSED(ok);
  qDebug() << "load data: liste size" <<interestPlacesList.size();
  return interestPlacesList;
  }
  

最后在插槽内回复完成我解析数据并填写列表。但这里的问题是，QFuture 在下载之前完成，因此列表始终为空。我怎样才能在执行 onReplyFinish 后返回填写的列表？

Answer 1

你可能会使这比你需要的更复杂。以下是我从网络上获取数据的方法。就我而言，我正在下载一个大的 ZIP 文件，将其写出然后解压缩，但基本步骤是相同的（为了清楚起见，我省略了很多特定代码）：

void HtmlDownloader::startDownload() {
    // Creates the network request and sets the destination URL
    QNetworkRequest request = QNetworkRequest();
    request.setUrl(mUrl);
    // Creates the network access manager and connects a custom slot to its
    // finished signal. Checks the return value for errors.
    QNetworkAccessManager *networkAccessManager =
            new QNetworkAccessManager(this);
    bool c = connect(networkAccessManager, SIGNAL(finished(QNetworkReply*)),
            this, SLOT(requestFinished(QNetworkReply*)));
    Q_ASSERT(c);
    // Indicate that the variable res isn't used in the rest of the app, to prevent
    // a compiler warning
    Q_UNUSED(c);
    // Sends the request
    QNetworkReply *reply = networkAccessManager->get(request);
    c = connect(reply, SIGNAL(downloadProgress(qint64,qint64)), this, SLOT(onDownloadProgress(qint64,qint64)));
    Q_ASSERT(c);
}
void HtmlDownloader::requestFinished(QNetworkReply *reply) {
// Handle the reply data...
// Check the network reply for errors
    if (reply->error() == QNetworkReply::NoError) {
        // use reply->readAll() or reply->read() to get the returned data
        // and process into a list. The list can't be returned but could
        // be sent as a payload of a signal, or stored in a data member and
        // a signal sent to indicate it is available.
    }
    reply->deleteLater();
}
void HtmlDownloader::onDownloadProgress(qint64 bytesRecieved, qint64 bytesTotal) {
    emit downloadProgress(bytesRecieved, bytesTotal);
}