信号槽弄得一团糟

Question

我正在尝试使用 Qt 创建一个图像保存应用程序。现在存根

class ImageSaver:public QObject
{
    int index;
    QWebPage * main_Page;
    QNetworkAccessManager * manager;
    QNetworkReply * reply;
    QString file_Name;
    QSet<QString> image_Addresses;
    QString web_Address;
    Q_OBJECT
signals:
    void image_Saved();
public slots:
    void request_Image();
    void on_Finished(bool status);
    void got_Reply(QNetworkReply * reply);
public:
    ImageSaver();
    void start();
};

ImageSaver::ImageSaver()
{
    index = 0;

    manager = new QNetworkAccessManager;

    reply = NULL;

    connect(main_Page,SIGNAL(loadFinished(bool)),this,SLOT(on_Finished(bool)));

    connect(manager,SIGNAL(finished(QNetworkReply*)),this,SLOT(got_Reply(QNetworkReply*)));

    connect(this,SIGNAL(image_Saved()),this,SLOT(request_Image()));
}

void ImageSaver::start()
{
    //loads the url 
    // In the end of the loading it will emit load_Finished(bool)
    // So that signal will execute on_Finished(bool)
}

void ImageSaver::request_Image()
{
    QString temp_Address = *(image_Addresses.begin()+index);

   //makes a request to the server to give the image "temp_Address"
   //When the server gives the reply signal finished(QNetworkReply*) will be emitted
   // this in turn will call the got_Reply(QNetworkReply*)
}

void ImageSaver::on_Finished(bool status)
{
       //collects all the images's url addresses, and pushes them in the list 
        //"image_Addresses"
        //Then emits image_Saved();
        //This signal will wake up the function request_Image()
}

void ImageSaver::got_Reply(QNetworkReply * reply)
{
    //Image is extracted from the reply and got saved in the same name as in the page
    //index got increased;
    //emits the signal image_Saved();
    //This signal will activate the function request_Image()
}

int main(int argc,char * argv[])
{
    QApplication app(argc,argv);
    ImageSaver a;
    a.start();
    return app.exec();
}

#include "main.moc"

简而言之，第一个调用是“start”。调用“on_Finished”，在此之前没有问题。所以所有图像文件的地址都被推入列表中。接下来是对 image[i] 的一一请求，并且回复图像已保存。这种事情屡屡发生。只有我遇到问题。在此操作中尤其是在保存图像时会出现崩溃。

我的假设是“信号槽”不像函数调用，它们或多或少像线程但在相同的函数（指针）上操作。因此，当一个信号请求画家时，画家已经在渲染某些东西，那么就会出现崩溃。

有人能说出崩溃背后的事实以及如何在不崩溃的情况下保存所有图像吗？

编辑： 你好，这是完整的代码。运行这个，然后连续单击消息框

    #include <QApplication>
#include <QDir>
#include <QImage>
#include <QObject>
#include <QMessageBox>
#include <QPainter>
#include <QPixmap>
#include <QSet>
#include <QTimer>
#include <QtNetwork/QNetworkAccessManager>
#include <QtNetwork/QNetworkReply>
#include <QtNetwork/QNetworkRequest>
#include <QtWebKit/QWebElement>
#include <QtWebKit/QWebFrame>
#include <QtWebKit/QWebPage>
#include <QUrl>

class ImageSaver:public QObject
{
    int index;
    QWebPage * main_Page;
    QNetworkAccessManager * manager;
    QNetworkReply * reply;
    QString file_Name;
    QSet<QString> image_Addresses;
    QString web_Address;
    Q_OBJECT
signals:
    void image_Saved();
public slots:
    void request_Image();
    void on_Finished(bool status);
    void got_Reply(QNetworkReply * reply);
public:
    ImageSaver();
    void start();
protected:
    //void show_Frame(QWebFrame * frame);
};

ImageSaver::ImageSaver()
{
    index = 0;

    this->main_Page = new QWebPage;

    manager = new QNetworkAccessManager;

    reply = NULL;

    connect(main_Page,SIGNAL(loadFinished(bool)),this,SLOT(on_Finished(bool)));

    connect(manager,SIGNAL(finished(QNetworkReply*)),this,SLOT(got_Reply(QNetworkReply*)));

    connect(this,SIGNAL(image_Saved()),this,SLOT(request_Image()));
}

void ImageSaver::start()
{
    web_Address = "yahoo.com";

    QDir dir;

    dir.mkdir(web_Address);

    QUrl url = QUrl::fromUserInput(web_Address);

    main_Page->mainFrame()->load(url);
}

void ImageSaver::request_Image()
{
    QString temp_Address = *(image_Addresses.begin()+index);

        int a = temp_Address.lastIndexOf("/");
        file_Name = temp_Address.mid(a+1);

        //Without the below message box, the program closes shortly
        //This message box is slowing down that effect
        QMessageBox hh;
        hh.setText(file_Name);
        hh.exec();
        QNetworkRequest request= QNetworkRequest(QUrl(temp_Address));
        request.setRawHeader("img","src");
        manager->get(request);
}

void ImageSaver::on_Finished(bool status)
{
    if(status)
    {
        QMessageBox mm;
        mm.setText("Finished");
        mm.exec();

        QWebElementCollection temp_Collection= main_Page->mainFrame()->findAllElements("*");

        for(int i=0;i<temp_Collection.count();++i)
        {
            QWebElement temp_Element = temp_Collection[i];
            if(temp_Element.tagName().contains("img",Qt::CaseInsensitive) && temp_Element.attributeNames().contains("src",Qt::CaseInsensitive))
            {
                QString image_Web_Address = temp_Element.attribute("src");
                if(!image_Addresses.contains(image_Web_Address))
                    image_Addresses.insert(image_Web_Address);
            }
        }
        emit image_Saved();
        QMessageBox kk;
        kk.setText("Image is going to be saved");
        kk.exec();
    }

    else
    {
        QMessageBox mm;
        mm.setText("Not ready");
        mm.exec();
    }

    QMessageBox mm;
    mm.setText("Getting out of finished");
    mm.exec();
}

void ImageSaver::got_Reply(QNetworkReply * reply)
{
    QImage image;
    if(image.load(static_cast<QIODevice *>(reply),0))
        image.save(web_Address+QDir::separator()+file_Name,0);

    ++index;
    emit image_Saved();
}

/*
void ImageSaver::show_Frame(QWebFrame * temp_Frame)
{
    QImage image(temp_Frame->contentsSize(),QImage::Format_ARGB32_Premultiplied);
    image.fill(Qt::transparent);

    QPainter painter(&image);
    painter.setRenderHint(QPainter::Antialiasing,true);
    painter.setRenderHint(QPainter::TextAntialiasing,true);
    painter.setRenderHint(QPainter::SmoothPixmapTransform,true);

    temp_Frame->documentElement().render(&painter);

    painter.end();

    foreach(QWebFrame * temp_Frame0,temp_Frame->childFrames())
        show_Frame(temp_Frame0);
}
*/

int main(int argc,char * argv[])
{
    QApplication app(argc,argv);

    ImageSaver a;
    a.start();

    return app.exec();
}

#include "main.moc"

这是 pro 文件

QT += webkit network

SOURCES += \
    main.cpp

Answer 1

您的代码崩溃是因为您读取的内容超出了 image_Addresses 集的边界。

void ImageSaver::request_Image()
{
    QString temp_Address = *(image_Addresses.begin()+index);
    ...

您在收到每个图像后递增索引，但代码中没有任何地方检查索引是否仍然小于 image_Addresses.size()，因此一旦取消引用 image_Addresses.begin()+index for index == image_Addresses.size，它就会崩溃()。

Answer 2

这个问题可能有很多解决方案。我认为您应该看看状态机框架。在简单的情况下，您可以仅使用布尔变量来检查是否可以继续。您还应该考虑当您忙于处理图像时该怎么办。您可以对请求进行排队或直接拒绝它们。您还可以实现线程，以便新的请求由新的线程提供服务。

PS 信号对我来说更像是事件而不是线程。

Answer 3

错误是什么？为什么末尾有 #include ？

仅供参考，您可以使用一个 QImage 类，其中包括从 QIODevice*（例如 QNetworkReply）保存和加载。在 Qt 这个庞大的框架中，很少需要重新发明轮子。