My function downloads multiple files concurrently, using QNetworkAccessManager. And then it should wait for all the QNetworkReply replies to finish before continuing with the rest of the code.
However I can't get QEventLoop to work with multiple connections, it either returns before all the replies finish, or just gets stuck in what I assume is an infinite loop.
This is my code:
void DownloadFiles(QStringList urls)
{
QNetworkAccessManager *manager = new QNetworkAccessManager(this);
QEventLoop loop;
QNetworkReply *replies[6];
for (int i = 0, i < urls.lenght(); i++){
replies[i] = manager->get(QNetworkRequest(QUrl(urls[i]));
connect(replies[i], SIGNAL(finished()), &loop, SLOT(quit()));
}
loop.exec(); // Wait here
// Rest of code
}
Another attempt, perhaps even more nonsensical:
void DownloadFiles(QStringList urls)
{
QNetworkAccessManager *manager = new QNetworkAccessManager(this);
QEventLoop loops[6];
QNetworkReply *replies[6];
for (int i = 0, i < urls.lenght(); i++){
replies[i] = manager->get(QNetworkRequest(QUrl(urls[i]));
connect(replies[i], SIGNAL(finished()), &loops[i], SLOT(quit()));
}
for (int i = 0; i < 6; i++)
loops[i]->exec(); // Wait here
// Rest of code
}
Again, my goal is to download multiple file concurrently, and wait for all of them to finish before continuing with the rest of the code.
You can use a counter to check how many times the signal was triggered.
#include <QtNetwork>
static void DownloadFiles(const QList<QUrl> & urls){
QNetworkAccessManager manager;
QList<QNetworkReply *> replies;
QEventLoop loop;
int total = urls.length();
for(const QUrl & url: urls){
QNetworkReply *reply = manager.get(QNetworkRequest(url));
QObject::connect(reply, &QNetworkReply::finished, [&total, &loop](){
total--;
if(total == 0){
loop.quit();
}
});
replies << reply;
}
loop.exec();
for(QNetworkReply *reply: replies){
qDebug() << "===============================";
qDebug() << "url:" << reply->url() << "\nhas error?" << (reply->error() != QNetworkReply::NoError);
qDebug() << "===============================";
}
qDebug() << "Completed";
qDeleteAll(replies.begin(), replies.end());
replies.clear();
}
int main(int argc, char *argv[]) {
QCoreApplication app(argc, argv);
QList<QUrl> urls { QUrl("https://www.qt.io/"),
QUrl("https://github.com/"),
QUrl("https://stackoverflow.com/") };
DownloadFiles(urls);
return 0;
}
output:
===============================
url: QUrl("https://www.qt.io/")
has error? false
===============================
===============================
url: QUrl("https://github.com/")
has error? false
===============================
===============================
url: QUrl("https://stackoverflow.com/")
has error? false
===============================
Completed