Qt execute multiple get with QNetworkAccessManager - c++

Question

I have to execute a lot of get requests and they have to be hadled in different ways. So far, I have this simply approach that works:
And here's the code for .h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = nullptr);
~MainWindow();
private slots:
void on_pushButton_clicked();
void on_pushButton_2_clicked();
void finish(QNetworkReply *reply);
void finish2(QNetworkReply *reply);
private:
Ui::MainWindow *ui;
QNetworkAccessManager* manager;
};
#endif // MAINWINDOW_H
And code for .cpp:
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
//First request here...
void MainWindow::on_pushButton_clicked()
{
manager = new QNetworkAccessManager(this);
connect(manager, &QNetworkAccessManager::finished, this, &MainWindow::finish);
manager->get(QNetworkRequest{QUrl{"http://www.link.com/path/"}});
}
//... is completed here
void MainWindow::finish(QNetworkReply *reply) {
if (reply->error()) {
ui->lineEdit->setText("error");
qDebug() << reply->errorString();
} else {
ui->lineEdit->setText(QString{reply->readAll()});
}
}
//Second request here...
void MainWindow::on_pushButton_2_clicked()
{
manager = new QNetworkAccessManager(this);
connect(manager, &QNetworkAccessManager::finished, this, &MainWindow::finish2);
manager->get(QNetworkRequest{QUrl{"https://ergast.com/api/f1/2008/5.json"}});
qDebug() << "chiamata";
}
//... is completed here
void MainWindow::finish2(QNetworkReply *reply) {
if (reply->error()) {
ui->lineEdit_2->setText("error");
qDebug() << reply->errorString();
} else {
ui->lineEdit_2->setText(QString{reply->readAll()});
}
}
When I press both buttons the requests happen but my UI blocks. I have tried this approach because I have seen in many examples that it's good to have a QNetworkAccessManager* manager; as private field and re-use it.
It does not seem by the way the best approach. Is there a proper way to do multiple calls?
Should I declare maybe an array of QNetworkAccessManager* and execute there all the calls?
I have also seen that there's the possibility to create a private field called QNetworkReply* reply; and then use it like this:
manager = new QNetworkAccessManager(this);
reply = manager->get(QNetworkRequest{QUrl{"http://www.link.com/path/"}});
connect(manager, &QNetworkReply::finished, this, &MainWindow::finish);
I think that this is equivalent to the method I am using but in this case I don't know how to handle multiple requests because I am bind to the finish method and I should implement all the logic there.

Answer 1

I have tested your code and I have not noticed that the GUI is blocked, in addition to using signals and slots you should not have that problem. However I see that you are creating dynamic memory unnecessarily, in the following code I connect the QNetworkReply to a slot, filter through the QUrl and delete the QNetworkReply:
*.h
...
private slots:
void on_pushButton_clicked();
void on_pushButton_2_clicked();
void onReplyfinished();
private:
Ui::MainWindow *ui;
QNetworkAccessManager *manager;
...
*.cpp
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
manager = new QNetworkAccessManager(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
QNetworkReply *reply = manager->get(QNetworkRequest{QUrl{"http://www.link.com/path/"}});
connect(reply, &QNetworkReply::finished, this, &MainWindow::onReplyfinished);
}
void MainWindow::on_pushButton_2_clicked()
{
QNetworkReply *reply = manager->get(QNetworkRequest{QUrl{"https://ergast.com/api/f1/2008/5.json"}});
connect(reply, &QNetworkReply::finished, this, &MainWindow::onReplyfinished);
}
void MainWindow::onReplyfinished()
{
QNetworkReply *reply = qobject_cast<QNetworkReply*>(sender());
if(reply->url() == QUrl{"http://www.link.com/path/"}){
ui->lineEdit->setText(reply->error() ? "error": reply->readAll());
}
else if (reply->url() == QUrl{"https://ergast.com/api/f1/2008/5.json"}){
ui->lineEdit_2->setText(reply->error() ? "error": reply->readAll());
}
reply->deleteLater();
}