The QNetworkAccessManager class in Qt handles network communication, including HTTP operations. The following steps demonstrate how to perform a basic HTTP GET request.

Step 1: Declare Members in the Header

Define the network menager instance and the slot to handle encoming responses.

private slots:
    void handleResponse(QNetworkReply *networkReply);

private:
    QNetworkAccessManager *httpClient;

Step 2: Initialize and Connect Signals

In the class constructor, instantiate the manager and connect the finished signal to the custom slot.

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    httpClient = new QNetworkAccessManager(this);

    // Bind the signal to the slot
    connect(httpClient, &QNetworkAccessManager::finished, 
            this, &MainWindow::handleResponse);
}

Step 3: Cleanup Resources

Ensure the manager is properly deallocated in the destructor.

MainWindow::~MainWindow()
{
    delete ui;
    delete httpClient;
}

Step 4: Implement the Resposne Handler

Process the reply, check for errors, read the payload, and schedule the reply object for deletion.

void MainWindow::handleResponse(QNetworkReply *networkReply)
{
    // Extract the HTTP status code
    int httpStatus = networkReply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();

    qDebug() << "Method:" << networkReply->operation();
    qDebug() << "Status:" << httpStatus;
    qDebug() << "Target URL:" << networkReply->url();
    qDebug() << "Headers:" << networkReply->rawHeaderList();

    if (httpStatus != 200 || networkReply->error() != QNetworkReply::NoError)
    {
        qDebug() << "Request failed:" << networkReply->errorString();
        networkReply->deleteLater();
        return;
    }

    // Read the response body
    QByteArray payload = networkReply->readAll();
    qDebug() << "Response Data:" << QString::fromUtf8(payload);

    // Free memory
    networkReply->deleteLater();
}

Step 5: Execute the GET Request

Create a request using a QUrl and pass it to the manager's get method.

QUrl targetUrl("https://api.example.com/data");
httpClient->get(QNetworkRequest(targetUrl));