参数传递QCoreApplication

Question

我正在尝试为一个web服务构建一个客户端。我的目标是每秒钟向我的服务器发送一个请求。我用这个库来帮助我：QHttp

我创建一个用信号链接到我的QCoreApplication app**，的计时器，并在计时器达到1秒*时发送请求。

下面是我是如何做到的，：

main.cpp

#include "request.h"

int main(int argc, char** argv) {

    QCoreApplication app(argc, argv);
    Request* request = new Request();
    request->sendRequestPeriodically(1000, app);


    return app.exec();
}

request.h

//lots of include before
class Request
{
    Q_OBJECT

public:
    Request();
    void sendRequestPeriodically (int time, QCoreApplication app);

public slots:
    void sendRequest (QCoreApplication app);

};

request.cpp

#include "request.h"

void Request::sendRequest (QCoreApplication app){
    using namespace qhttp::client;
    QHttpClient client(&app);
    QUrl        server("http://127.0.0.1:8080/?Clearance");

    client.request(qhttp::EHTTP_GET, server, [](QHttpResponse* res) {
        // response handler, called when the incoming HTTP headers are ready


        // gather HTTP response data (HTTP body)
        res->collectData();

        // when all data in HTTP response have been read:
        res->onEnd([res]() {
            // print the XML body of the response
            qDebug("\nreceived %d bytes of http body:\n%s\n",
                    res->collectedData().size(),
                    res->collectedData().constData()
                  );

            // done! now quit the application
            //qApp->quit();
        });

    });

    // set a timeout for the http connection
    client.setConnectingTimeOut(10000, []{
        qDebug("connecting to HTTP server timed out!");
        qApp->quit();
    });
}

void Request::sendRequestPeriodically(int time, QCoreApplication app){
    QTimer *timer = new QTimer(this);
    QObject::connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest(app)));
    timer->start(time); //time specified in ms
}

Request::Request()
{

}

我发现了这些错误：

C:\Qt\5.7\mingw53_32\include\QtCore\qcoreapplication.h:211: erreur : 'QCoreApplication::QCoreApplication(const QCoreApplication&)' is private
     Q_DISABLE_COPY(QCoreApplication)

C:\Users\ebelloei\Documents\qhttp\example\client-aircraft\main.cpp:7: erreur : use of deleted function 'QCoreApplication::QCoreApplication(const QCoreApplication&)'

我对Qt并不熟悉，但我认为这是因为我不能在参数上通过我的QCoreApplication，对吗？

Answer 1

首先，如果您需要访问全局应用程序实例，则不应该传递它。使用qApp宏或QCoreApplication::instance()。

但这不是重点：QHttpClient client实例是一个局部变量，它的生存期由编译器管理。没有必要给它父母。当client退出时，sendRequest就会被销毁:由于这一点，您的sendRequest实际上是不操作的。

您的connect语句中也有错误:不能使用旧的样式connect语法传递参数值：

// Wrong: the connection fails and does nothing.
connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest(foo)));
// Qt 5
connect(timer, &QTimer::timeout, this, [=]{ sendRequest(foo); });
// Qt 4
this->foo = foo;
connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest()));
  // sendRequest would then use this->foo

理想情况下，您应该重新设计代码以使用QNetworkAccessManager。如果没有，则必须将QHttpClient实例保持在main中。

int main(int argc, char** argv) {
    QCoreApplication app(argc, argv);
    qhttp::client::QHttpClient client;
    auto request = new Request(&client);
    request->sendRequestPeriodically(1000);
    return app.exec();
}

然后：

class Request : public QObject
{
    Q_OBJECT
    QTimer m_timer{this};
    qhttp::client::QHttpClient *m_client;
public:
    explicit Request(qhttp::client::QHttpClient *client);
    void sendRequestPeriodically(int time);
    void sendRequest();
};

Request::Request(qhttp::client::QHttpClient *client) :
    QObject{client},
    m_client{client}
{
    QObject::connect(&m_timer, &QTimer::timeout, this, &Request::sendRequest);
}

void Request::sendRequestPeriodically(int time) {
    timer->start(time);
}

void Request::sendRequest() {
    QUrl server("http://127.0.0.1:8080/?Clearance");

    m_client->request(qhttp::EHTTP_GET, server, [](QHttpResponse* res) {
      ...
    });
}

Answer 2

不能通过复制构造函数传递复制QCoreApplication对象，必须传递指向QCoreApplication的指针。

所有"QCoreApplication应用程序“都应该替换为"QCoreApplication * app”，对这些函数的调用必须包括一个指向应用程序的指针，而不是它的副本。

request.h

//lots of include before
class Request
{
    Q_OBJECT

public:
    Request();
    void sendRequestPeriodically (int time, QCoreApplication *app);

public slots:
    void sendRequest (QCoreApplication *app);

};

request.cpp

#include "request.h"

void Request::sendRequest (QCoreApplication *app){
    using namespace qhttp::client;
    QHttpClient client(app);
    QUrl        server("http://127.0.0.1:8080/?Clearance");

    client.request(qhttp::EHTTP_GET, server, [](QHttpResponse* res) {
        // response handler, called when the incoming HTTP headers are ready


        // gather HTTP response data (HTTP body)
        res->collectData();

        // when all data in HTTP response have been read:
        res->onEnd([res]() {
            // print the XML body of the response
            qDebug("\nreceived %d bytes of http body:\n%s\n",
                    res->collectedData().size(),
                    res->collectedData().constData()
                  );

            // done! now quit the application
            //qApp->quit();
        });

    });

    // set a timeout for the http connection
    client.setConnectingTimeOut(10000, []{
        qDebug("connecting to HTTP server timed out!");
        qApp->quit();
    });
}

void Request::sendRequestPeriodically(int time, QCoreApplication app){
    QTimer *timer = new QTimer(this);
    QObject::connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest(app)));
    timer->start(time); //time specified in ms
}

Request::Request()
{

}

main.cpp

#include "request.h"

int main(int argc, char** argv) {

    QCoreApplication app(argc, argv);
    Request* request = new Request();
    request->sendRequestPeriodically(1000, &app);

    return app.exec();
}

编辑如KubaOber所说，您的代码中还有更多的问题，请阅读他的答案