关于 Qt 中 app.exec() 和循环的问题

Question

app.exec() 不是返回main() 的无限循环吗？

我想循环下面的服务器客户端通信，但它只执行一个，然后主函数以app.exec()结束

我是 Qt 和 C++ 的新手，我该如何管理这个循环？

int main(int argc, char *argv[])
{
    cout << "Waiting for the next request " << endl;
    QApplication app(argc, argv);

    //  Prepare our context and socket
    zmq::context_t context(1);
    zmq::socket_t socket(context, ZMQ_REP);
    socket.bind("tcp://*:2424");
    zmq::message_t request;


    QQmlApplicationEngine engine;

    VideoStreamer videoStreamer;
    imageProvider *liveOriginalImageProvider(new imageProvider);
    imageProvider *liveMaskedImageProvider(new imageProvider);

    //********SERVER CLIENT COMMUNICATION BEGINS******//

    // Wait for next request from client
    cout << "Waiting for the next request ." << endl;
    socket.recv(&request);
    cout << "Waiting for the next request.. " << endl;
    string replyMessage = string(static_cast<char *>(request.data()), request.size());

    // Print out received message
    cout << "Received from client (Python): " + replyMessage << endl;

    //  See the gradual sending/replying from client
    sleep(1);

    //  Send reply back to client
    string msgToClient("W");
    zmq::message_t reply(msgToClient.size());
    memcpy((void *) reply.data(), (msgToClient.c_str()), msgToClient.size());
    socket.send(reply);

    //*********SERVER CLIENT COMMUNICATION ENDS**********//

    engine.rootContext()->setContextProperty("VideoStreamer",&videoStreamer);
    engine.rootContext()->setContextProperty("liveOriginalImageProvider",liveOriginalImageProvider);
    engine.rootContext()->setContextProperty("liveMaskedImageProvider",liveMaskedImageProvider);

    engine.addImageProvider("liveOriginal",liveOriginalImageProvider);
    engine.addImageProvider("liveMasked",liveMaskedImageProvider);


    const QUrl url(QStringLiteral("qrc:/main.qml"));
    engine.load(url);

    QObject::connect(&videoStreamer,&VideoStreamer::originalImage,liveOriginalImageProvider,&imageProvider::updateImage);
    QObject::connect(&videoStreamer,&VideoStreamer::maskedImage,liveMaskedImageProvider,&imageProvider::updateImage);

    return app.exec();
}

---------更新---------

我在 thread.h

中创建了这个线程

class MyThread : public QThread{
public slots:
    void run();
};

在thread.cpp中我声明了方法：

void MyThread :: run() {
    //  Prepare our context and socket
    zmq::context_t context(1);
    zmq::socket_t socket(context, ZMQ_REP);
    socket.bind("tcp://*:2424");
    zmq::message_t request;

    //********SERVER CLIENT COMMUNICATION BEGINS******//

    // Wait for next request from client
    cout << "Waiting for the next request ." << endl;
    socket.recv(&request);
    cout << "Waiting for the next request.. " << endl;
    string replyMessage = string(static_cast<char *>(request.data()), request.size());

    // Print out received message
    cout << "Received from client (Python): " + replyMessage << endl;

    //  See the gradual sending/replying from client
    sleep(1);

    //  Send reply back to client
    string msgToClient("W");
    zmq::message_t reply(msgToClient.size());
    memcpy((void *) reply.data(), (msgToClient.c_str()), msgToClient.size());
    socket.send(reply);

    exec();
    //*********SERVER CLIENT COMMUNICATION ENDS**********//
}

在 ma​​in.cpp 我称之为：

QThread *thread = new QThread();

MyThread *myThread = new MyThread();
myThread->moveToThread(thread);
myThread->connect(thread, SIGNAL(started()), myThread, SLOT(run()));

thread->start();

我得到Error: Class declaration lacks Q_OBJECT macro. QThread 不继承 QObject 吗？如何正确调用循环？

Answer 1

我目前从事的主要项目之一使用 Qt 和 ZMQ - 您的 ZMQ 套接字需要位于在应用程序事件循环上运行的 QObject 内，而不是在应用程序的 main() 函数内

这是一个非常简略视图，说明我们的一个 ZMQ 套接字如何在 Qt 事件循环上进行通信 - 应用程序有一个 ZMQ_SUB 套接字连接到另一端的 ZMQ_PUB 套接字发布事件从硬件接口

int main(int argc, char* argv[])
{
   QApplication app(argc, argv);
   ...
   ConnectionManager connMgr; // Create connection class - is a QObject subclass
   connMgr.connect(target);

   MainWindow mainWin; // Create GUI classes

   return app.exec();
}

void ConnectionManager::connect(std::string target)
{
    context = zmq_ctx_new();

    zsocket = zmq_socket(context, ZMQ_SUB);
    zmq_connect(zsocket, (connection + ":" + REQUEST_PORT).c_str());
    ...

    QTimer pollTimer;
    pollTimer.callOnTimeout(this, &ConnectionManager::onPollTimer);
    pollTimer.start(100);
}

void ConnectionManager::onPollTimer()
{
    uint16_t length = 0;

    const size_t buffer_length = 1024;
    uint8_t* buffer = new uint8_t[buffer_length];

    do
    {
        int64_t more = 0;
        size_t more_size = sizeof more;
        auto len = zmq_recv(zsocket, buffer + length, buffer_length - length, ZMQ_NOBLOCK);
        if (len == -1)
        {
            return;
        }
        else if (len > 0)
        {
            length += len;
            auto rc = zmq_getsockopt(socket, ZMQ_RCVMORE, &more, &more_size);
        }
    } while (more);

    std::cout << "Received" << length << "bytes";
    HandleMessage(buffer, length); // Process the incoming message
}

本质上，app.exec() 确实创建了一个无限循环，但该循环存在于 QApplication 对象中，而不是重复运行调用它的 main() 函数并利用该循环的循环您的应用程序应创建QObject 子类的其他实例，并使用信号/插槽/QEvent/QTimer 机制来执行操作以响应用户操作/输入事件/时间间隔