Qt基于Qt示例从QThread下载文件不起作用
Qt Download Files from QThread Based On Qt Example Doesn't work
嗨,我构建了一个简单的例子,剔除了所有不相关的代码,只留下有问题的代码一般来说,我有执行线程的应用程序,在这个线程工作器内,我放置了下载代码,应该下载30多个文件,这是基于Qt给出的下载示例,问题是QNetworkAccessManager槽永远不会调用。你能告诉我我哪里做错了吗?
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*)), this, 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: %sn",
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: %sn",
url.toEncoded().constData(),
qPrintable(reply->errorString()));
} else {
QString filename = saveFileName(url);
if (saveToDisk(filename, reply))
printf("Download of %s succeeded (saved to %s)n",
url.toEncoded().constData(), 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();
}
尽管您在代码中调用了"networkMgr->get(request)",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"QThread::run()"方法的最底部,以进入QNetworkAccessManager需要能够工作的线程中的事件循环。这也可以防止线程过早地完成它的执行。你的代码看起来像这样:
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,它甚至不会将信号连接到插槽。请参阅调试器输出,以在运行时(应用程序输出选项卡)获得有关该问题的警告。
所以,不用
connect(networkMgr, SIGNAL(readyRead()), this, SLOT(downloadFinished(QNetworkReply*)));
connect(networkMgr, SIGNAL(finished(QNetworkReply*)), this, SLOT(downloadFinished(QNetworkReply*)));
通过QNetworkReply的error
信号处理错误。在你get
之后,你可以连接到信号。
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