如何從另一個線程中引發的Boost信號更新Qt GUI？

Question

我有一個運行在單獨的線程的數據獲取程序的普通的C ++對象，並使用命名為升壓信號通知過程acquisitionStageChangedEvent具有以下簽名： boost::signal2::signal<void(const std::string &)> 。 如何在沒有跨線程異常的情況下在新線程中開始獲取並使用此信息更新UI？

Answer 1

在信號處理程序中將std::atomic<bool>為true，然后從QTimer檢查該標志。

Answer 2

這是一個有關如何在進度更新過程中和任務結束時啟動后台線程並更新UI的工作示例：

namespace Ui
{
    class DtacqAcquisitionWidget;
}

class DtacqAcquisitionWidget : public QWidget
{
    Q_OBJECT

public:
    explicit AcquisitionWidget(QWidget *parent = 0);

   ~DtacqAcquisitionWidget();

private slots:

    void on_pushButtonStart_clicked();

    void onDtacqChangeState(const QString &stage);

    /*... Other slots here */
private:
    Ui::AcquisitionWidget *ui;

    QFutureWatcher<void>  *m_future_watcher; // This is to be able to run UI code at the end of the background thread

    anlytcs::Dt100Acq m_dtacq; // The plain C++ object that raises the boost signal 'acquisitionStageChangedEvent'
};

在.cpp文件中：

DtacqAcquisitionWidget::DtacqAcquisitionWidget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::DtacqAcquisitionWidget)
{
    ui->setupUi(this);

    // Run the 'onAcquisitionFinished' slot at the end of the thread
    m_future_watcher = new QFutureWatcher<void>(this);
    connect(m_future_watcher, SIGNAL(finished()), this, SLOT(onAcquisitionFinished()));

    // Acquisition stages update
    m_dtacq.acquisitionStageChangedEvent.connect([this](const std::string &stage)
    {
        this->onDtacqChangeState(QString::fromStdString(stage));
    });
}

void DtacqAcquisitionWidget::on_pushButtonStart_clicked()  // Starting the acquisition
{
    ui->pushButtonStop->setEnabled(true);
    ui->pushButtonStart->setEnabled(false);
    ui->progressBar->setValue(0);

    // Start the acquisition in a new thread
    QFuture<void> f = QtConcurrent::run(this, &DtacqAcquisitionWidget::acquireChannelData);    
    m_future_watcher->setFuture(f);
}

void DtacqAcquisitionWidget::onDtacqChangeState(const QString &stage)
{
    if (thread() != QThread::currentThread())
    {      
        QMetaObject::invokeMethod(this, "onDtacqChangeState", 
            Qt::BlockingQueuedConnection, Q_ARG(QString, stage));
    }
    else
    {
        ui->labelDtacqState->setText(stage);
        ui->progressBar->setValue(ui->progressBar->value() + 40);
    }    
}

void DtacqAcquisitionWidget::onAcquisitionFinished()
{
    // Set what to update here in the GUI here when the acquisition thread finishes     
    ui->labelDtacqState->setText("DONE!");
}

void DtacqAcquisitionWidget::acquireChannelData()
{
    // This is running on a background thread (Non UI thread)
    double time_sec = ui->spinBoxAcqTimeSec->value();
    uint32_t channel_mask = getChannelMask();

    std::string data_path = "C:/Users/pardinad/Desktop/DtacqData/";
    m_dtacq.startAcquisition(time_sec, channel_mask, 250);
    ui->labelDtacqState->setText("Acquisition Started!");

    if(m_dtacq.completeAcquisition())   
    {
        for (auto & dch : m_dtacq.dataChannels())
        {
            std::stringstream ss;
            ss << data_path << std::setw(2) << std::setfill('0') << dch.channelNumber() << ".DAT";
            std::string ch_file = ss.str();
            dch.saveToFile(ch_file);
        }
    }
}