MainWindow from code from the main.cpp in Qt

Question

Want to understand the difference in code between the MainWindow and the main.cpp. Specifically, how a chunk of code written exclusively in the m

Answer 1

You can put all of this code in constructor of your QMainWindow and retaining lambda functions as-is.

Another more clean way would be transforming those lambda functions into private slots. Using this way, you should define networkManager as a class member of your QMainWindow class and also it should be allocated in heap memory not stack. To get this done, just define a QNetworkManager* class member and initialize it in your QMainWindow constructor.

this->networkManager = new QNetworkManager(this);

Once it's been initialized, you can use it in all slots of your QMainWindow class.

A simple rule of thumb is: all shared variables among lambda functions and the main scope should be class members in this way.

---

The code. (I tested it and works fine)

main.cpp

#include "mainwindow.h"
#include 

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

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

    ui->lineEditGender->setReadOnly(true);
    ui->lineEditRegion->setReadOnly(true);
    ui->lineEditName->setReadOnly(true);

    networkManager = new QNetworkAccessManager(this);

    connect(networkManager, &QNetworkAccessManager::finished, this, &MainWindow::onNetworkManagerFinished);
    connect(ui->btnGetName, &QPushButton::clicked, this, &MainWindow::onBtnGetNameClicked);
}

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

void MainWindow::onNetworkManagerFinished(QNetworkReply *reply)
{
    if(reply->error() != QNetworkReply::NoError){
        ui->lineEditName->setText("Error");
        ui->lineEditGender->setText("Error");
        ui->lineEditRegion->setText("Error");

        networkManager->clearAccessCache();
    } else {
        //parse the reply JSON and display result in the UI
        QJsonObject jsonObject = QJsonDocument::fromJson(reply->readAll()).object();
        QString fullName= jsonObject["name"].toString();
        fullName.append(" ");
        fullName.append(jsonObject["surname"].toString());
        ui->lineEditName->setText(fullName);
        ui->lineEditGender->setText(jsonObject["gender"].toString());
        ui->lineEditRegion->setText(jsonObject["region"].toString());
    }
    ui->btnGetName->setEnabled(true);
    reply->deleteLater();
}

void MainWindow::onBtnGetNameClicked()
{
    QUrlQuery query;
    query.addQueryItem("amount", "1");
    query.addQueryItem("region", "United States");
    QUrl url("http://uinames.com/api/");
    url.setQuery(query);
    QNetworkRequest networkRequest(url);

    //send GET request when the button is clicked
    networkManager->get(networkRequest);
    ui->btnGetName->setEnabled(false);

    ui->lineEditName->setText("Loading. . .");
    ui->lineEditGender->setText("Loading. . .");
    ui->lineEditRegion->setText("Loading. . .");
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include 
#include 
#include 
#include 
#include 
#include 
#include 

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
    void onNetworkManagerFinished(QNetworkReply* reply);
    void onBtnGetNameClicked();

private:
    Ui::MainWindow *ui;
    QNetworkAccessManager *networkManager;
};

#endif // MAINWINDOW_H