Qt从基于Qt示例的QThread下载文件不起作用

问题描述

|| 嗨，我建立了一个简单的示例，将所有不相关的代码条带化，仅保留有问题的代码 通常，我有执行线程的应用程序，并且在此线程工作器内，我放置了应该下载30个以上文件的下载代码，这是根据Qt给出的下载示例得出的，问题是QNetworkAccessManager插槽从不调用。 你能告诉我我在做什么错吗？

class MainWindowContainer : public QMainWindow 
{
    Q_OBJECT

public:
    MainWindowContainer(QWidget *parent = 0);


 public slots:
    void InvokeDownloadThread();

 private:
    QPushButton *pushButtonInvokeThread;
    PhotosDownloadWorker* pm_hotosDownloadWorker;
  };

#include <QtGui>
#include \"MainWindowContainer.h\"

MainWindowContainer::MainWindowContainer(QWidget* parent) : 
                                    QMainWindow(parent) 
{
    pushButtonInvokeThread  = new QPushButton(this); 
    QHBoxLayout *layout = new QHBoxLayout;
    layout->addWidget(pushButtonInvokeThread);
    setLayout(layout);
    QObject::connect(pushButtonInvokeThread,SIGNAL(clicked()),this,SLOT(InvokeDownloadThread()));

}
void MainWindowContainer::InvokeDownloadThread()
{
     pm_hotosDownloadWorker = new PhotosDownloadWorker(this);
     pm_hotosDownloadWorker->Execute();
}

class PhotosDownloadWorker : public QThread 
{
    Q_OBJECT

 public :
    PhotosDownloadWorker(QObject *parent);
    ~PhotosDownloadWorker();
    void  Execute();
    void append(const QStringList &urlList);
    bool saveToDisk(const QString &filename,QIODevice *data);
    QString saveFileName(const QUrl &url);

 protected:
    void run();

private:
    bool m_abort;
     QList<QNetworkReply *> currentDownloads;
     QFile output;
     QNetworkAccessManager* networkMgr ;  

  public slots:
     void downloadFinished(QNetworkReply *reply);
     void startNextDownload(const QUrl &url);



};

#include \"PhotosDownloadWorker.h\"
PhotosDownloadWorker::PhotosDownloadWorker(QObject *parent)
    : QThread(parent)
{
    m_abort = false;
    networkMgr = new QNetworkAccessManager(this);
    connect(networkMgr,SIGNAL(finished(QNetworkReply*)),SLOT(downloadFinished(QNetworkReply*)));
 }

 PhotosDownloadWorker::~PhotosDownloadWorker()
{
   m_abort = true; 
    wait();
}

void PhotosDownloadWorker::Execute()
{
    m_abort = false;
    start();
}
void PhotosDownloadWorker::run()
{
    QStringList m_urlList;

    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");
    m_urlList.append(\"http://....xxxx......jpg\");

    // x 30 
    append(m_urlList);
}


void PhotosDownloadWorker::append(const QStringList &urlList)
{
    foreach (QString url,urlList)
    {
         startNextDownload(QUrl::fromEncoded(url.toLocal8Bit()));
    }
 }

void PhotosDownloadWorker::startNextDownload(const QUrl &url)
{
    QNetworkRequest request(url);
    QNetworkReply *reply = networkMgr->get(request);
    currentDownloads.append(reply);
}
 bool PhotosDownloadWorker::saveToDisk(const QString &filename,QIODevice *data)
{
    QFile file(filename);
    if (!file.open(QIODevice::WriteOnly)) {
        fprintf(stderr,\"Could not open %s for writing: %s\\n\",qPrintable(filename),qPrintable(file.errorString()));
        return false;
    }

    file.write(data->readAll());
    file.close();

    return true;
}

void PhotosDownloadWorker::downloadFinished(QNetworkReply *reply)
{
    QUrl url = reply->url();
    if (reply->error()) {
        fprintf(stderr,\"Download of %s failed: %s\\n\",url.toEncoded().constData(),qPrintable(reply->errorString()));
    } else {
        QString filename = saveFileName(url);
        if (saveToDisk(filename,reply))
            printf(\"Download of %s succeeded (saved to %s)\\n\",qPrintable(filename));
    }

     reply->deleteLater();
     currentDownloads.removeAll(reply);
     if (currentDownloads.isEmpty())
     {

         this->exit();
     }

}
 QString PhotosDownloadWorker::saveFileName(const QUrl &url)
{
    QString path = url.path();
    QString basename = QFileInfo(path).fileName();

    if (basename.isEmpty())
        basename = \"download\";

    if (QFile::exists(basename)) {
        // already exists,don\'t overwrite
        int i = 0;
        basename += \'.\';
        while (QFile::exists(basename + QString::number(i)))
            ++i;

        basename += QString::number(i);
    }

    return basename;
}

//main

#include \"MainWindowContainer.h\"

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

     QApplication app(argc,argv);
     MainWindowContainer mainWindowContainer;
     mainWindowContainer.show();
     return app.exec();
 }

    

解决方法

尽管您在代码中调用了“ networkMgr-> get（请求）\”，但您的线程可能在实际下载开始之前就退出了。尝试将\“ exec（）\”调用放在您的\“ QThread :: run（）\”方法的最底部，以在您的线程中输入事件循环，QNetworkAccessManager必须能够运行该事件循环。这也将阻止线程过早地完成其执行。您的代码如下所示：

void PhotosDownloadWorker::run()
{
  QStringList m_urlList;

  m_urlList.append(\"http://....xxxx......jpg\");
  m_urlList.append(\"http://....xxxx......jpg\");    
  // x 30 
  append(m_urlList);

  exec();
}

    ,我认为如果参数列表不匹配，它甚至都不会将信号连接到插槽。有关运行时的警告，请参见调试器输出（应用程序输出选项卡）。 所以，代替

connect(networkMgr,SIGNAL(readyRead()),this,SLOT(downloadFinished(QNetworkReply*)));

做

connect(networkMgr,SIGNAL(finished(QNetworkReply*)),SLOT(downloadFinished(QNetworkReply*)));

通过QNetworkReply的

error

信号处理错误。

get

之后，您可以连接到信号。