QThread的复杂用法-

Question

I have wrote an app in QT/C++. This app have multiple classes to manage window, treewidget.. and a custom class.

The goal of the app is to be android file transfer -like in QT/c++ on MacOSx.

Currently the entire app is working in one thread which include the UI management and the android device management. The android device access is managed by a class named DeviceManager. This class will mostly open the device, read it, add/delete files....

What I want to do is to create a thread which will handle all method defined in the DeviceManager. I want the UI on one thread and the devicemngr in a separate thread.

Here is my current code :

main.cpp

int main(int argc, char *argv[])
{
    PULS_mtp_error_t error = ERROR_GENERAL;
    QThread PulsDeviceThread;

    QApplication app(argc, argv);

    DeviceMngr *MyMtp = new DeviceMngr;
    error = MyMtp->OpenDevice();
    ...
    MainUI MyWindow(*MyMtp);
    MyWindow.show();
    return app.exec();

}

the MainUI class is defined as below

MainUI::MainUI(DeviceMngr& device) :
    m_device(device)
{

    m_closing = false;

    setWindowTitle(QString::fromUtf8("PULS"));
    resize(800,600);
    setUnifiedTitleAndToolBarOnMac(true);
    /* Creation of the Top bar section */
    createBackForwardButton();
    createLogoSection();
    createAddFolder();

    QWidget *TopBarWidget = new QWidget();
    TopBarWidget->setFixedHeight(61);
    QHBoxLayout *TopBarLayout = new QHBoxLayout(TopBarWidget);
    TopBarLayout->addWidget(BackForwardSection);
    TopBarLayout->addWidget(LogoSection);
    TopBarLayout->addWidget(AddFolderSection);

    /* Creation of Tree View Section */
    createTreeView();

    /* Creation of the bottom bar section */
    createInfoSection();

    /*about*/
    aboutAction = new QAction(tr("&About"),this);
    connect(aboutAction, SIGNAL(triggered()),this ,SLOT(aboutPuls()));

    QMenu *helpMenu = new QMenu("Help", this);
    helpMenu->addAction(aboutAction);
    menuBar()->addMenu(helpMenu);

    /*Overall Layout*/
    QWidget *MainWindowWidget = new QWidget();
    QVBoxLayout *MainWindowLayout = new QVBoxLayout(MainWindowWidget);

    MainWindowLayout->setSpacing(0);
    MainWindowLayout->addWidget(TopBarWidget);
    MainWindowLayout->addWidget(TreeViewSection);
    MainWindowLayout->addWidget(CreateInfoSection);

    setCentralWidget(MainWindowWidget);

    PulsUnplugged = false;
#if 1
    activeTimer = new QTimer(this);
    activeTimer->setSingleShot(false);
    activeTimer->setInterval(200);
    connect(activeTimer, SIGNAL(timeout()), this, SLOT(PulsDetection()));
    activeTimer->start();
#endif
    show();
}

Some of the method such as createTreeView will use the m_device to access also to the device.

void MainUI::createTreeView()
{

    TreeViewSection = new QWidget();

    QVBoxLayout *TreeViewLayout = new QVBoxLayout(TreeViewSection);

    MyTreeWidget = new MyNewTreeWidget(m_device, *this);

    TreeViewLayout->addWidget(MyTreeWidget);
}

MyNewTreeWidget will also need to access to the DeviceMngr class.

Most of class used for the UI management can access to the DeviceMngr class. I don't know how to use the QThread to make sure that all UI classes can access to the DeviceMngr class.

I was thinking to create a Qthread in the main.cpp but I do not see how to add slots/signals in the main.cpp and DeviceMngr will have signals/slots to discuss with all other thread. the main will need for example to open the device and receive the result.

Do I need to create all signal/slot connection in the main or I can just add what I need in the different classes and create the connections when needed.

Any idea ? I have tried a first implementation but it not really working fine.

Thanks

Answer 1

I would suggest creating the worker thread and moving your DeviceMngr to it. Its slots (and whole event loop) will run in the context of the thread and you must use Qt's signal/slot mechanism that will ensure thread safe access to DeviceMngr from other QObjects.

int main(...) {
    // ...
    QThread MtpThread;
    DeviceMngr MyMtp;
    MyMtp.moveToThread(&MtpThread);

    // connect signals/slots of DeviceMngr
    // ...

    // launch the thread
    MtpThread.start();

    // should you need to call slots of DeviceMngr from main use metacalls
    QMetaObject::invokeMethod(&MyMtp, "nameOfSlot");

    // run application

    // in the end join
    MtpThread.quit(); // stop event queue
    MtpThread.wait(); // join the thread
}

I hope you get the idea. Key is moveToThread() and metacalls.