void MainWindow::on_startButton_clicked()
{
QNetworkAccessManager *nam = new QNetworkAccessManager(this);
QNetworkReply *re = nam->get(QNetworkRequest(QUrl("http://somesite/ai/iai.jpg")));
QEventLoop loop;
QObject::connect(reply, SIGNAL(readyRead()), &loop, SLOT(quit()));
loop.exec();
ui->dbgOut->insertHtml("<font color='green'>OK</font><br>");
ui->dbgOut->insertHtml("##################################");
//save
QFile file("C:\\a.bin");
file.open(QIODevice::WriteOnly);
file.write(re->readAll());
file.close();
}
我有两个问题:
当我点击按钮时,它会下载文件,但不会将它们写入硬盘。我可以等5分钟,10分钟,什么都没有。此时,整个文件存储在程序存储器中。如果我关闭我的程序,它们将保存在磁盘上。
根本不保存大文件(~500MB)。当我关闭我的程序时,它会立即崩溃。
我如何编辑它以便我的程序“实时”保存下载的文件?
答案 0 :(得分:4)
非交互性是因为未知大小的设备上的re->readAll()
是阻止呼叫。它将继续阅读,直到请求完成。
大文件的问题与保存文件的字节数组的增长有关。在某些时候,你的字节数组将是400MB,然后它必须增长到2倍大小,所以你必须一次保持~1GB,两个大块,并且由于地址空间碎片分配请求将失败,程序崩溃。
对代码进行细微更改会产生所需的行为:您立即开始阅读和写作,并将两者联系起来:
class MainWindow {
...
// You shouldn't be creating a new network access manager for each request.
QScopedPointer<QNetworkAccessManager> m_nam;
...
};
void MainWindow::handleError(const QNetworkReply *) { ... }
void MainWindow::handleError(const QFile *) { ... }
void MainWindow::on_startButton_clicked()
{
// Lazily create the network access manager once.
if (!m_nam) m_nam.reset(new QNetworkAccessManager);
// The file is destructed, and thus flushed and closed, when the
// last shared pointer to this file is destructed.
QSharedPointer<QFile> output(new QFile("C:\\a.bin"));
if (!output->open(QIODevice::WriteOnly)) return;
QNetworkReply *reply = m_nam->get(QNetworkRequest(QUrl("http://somesite/ai/iai.jpg")));
// The lambda syntax creates a functor object that holds a copy
// of the reply pointer and the output file pointer.
// This functor will be destructed when the reply is destructed.
QObject::connect(reply, &QIODevice::readyRead, [this, output, reply]{
QByteArray data(reply->bytesAvailable(), Qt::Uninitialized);
qint64 in = reply->read(data.data(), data.size());
qint64 out = output->write(in);
if (in < 0) {
handleError(reply);
reply->deleteLater();
}
else if (out != in) {
handleError(output.data());
reply->deleteLater();
}
});
// The reply will self-destruct when finished, thus deleting the file
// instance.
QObject::connect(reply, &QNetworkReply::finished, reply, &QObject::deleteLater);
}