Evgenii Legotckoi
Evgenii LegotckoiJan. 2, 2016, 10:33 a.m.

Qt/C++ - Lesson 041. JSON file – How to get from site and parsing it

In the process of writing programs EColor appeared a problem in which it was necessary in some way to notify the user that a new version of the program. The solution to this problem was the presence of JSON file on the site. With QNetworkAccessManager get a JSON file and produce his analysis, thanks to the class library Qt: QJsonDocument , QJsonObject , QJsonArray . In the case of the program on the website EColor contains JSON file with the name of the program, the full version in string form and three entities to the major part of the version, minor and patch version. When parsing the file is compared with the current version of the program that is on the website. If the site is lined with a newer version, the program will notify the user.


For example, at http://www.evileg.ru/it_example.json JSON file is located on a site with the following content:

{
  "departament": "it",
  "employees": [
    {"firstName": "John", "lastName": "Doe"},
    {"fisrtName": "Michael", "lastName": "Smith"},
    {"firstName": "Anna", "lastName": "Jones"}
    ],
  "number" : 3
}

At the root of the object file is located three objects, the second of which is an array. The first object - a string property " departament ", which contains the name of the department. The second object - an array containing the names of employees. A third object - is the employees number of type Integer .

Project structure for JSON parsing

  • JSONParser.pro - the profile of the project;
  • main.cpp - the main project source code file;
  • widget.h - header file of the application window, which contains a QTextEdit field, which will be placed in the result of parsing the file;
  • widget.cpp - source file with QNetworkAccessManager.
  • widget.ui - file interface.

JSONParser.pro

Do not forget to connect the network module to the profile of the project, to be able to work with the class QNetworkAccessManager .

#-------------------------------------------------
#
# Project created by QtCreator 2016-01-02T13:12:55
#
#-------------------------------------------------

QT       += core gui network

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = JSONParser
TEMPLATE = app


SOURCES += main.cpp\
        widget.cpp

HEADERS  += widget.h

FORMS    += widget.ui

widget.h

Connect class QNetworkAccessManager , also declared in the header file SLOT o nResult(QNetworkReply * reply) , which will be parsed JSON file when receiving a response from the site with the contents of the file.

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QNetworkAccessManager>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

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

private slots:
    // Обработчик данных полученных от объекта QNetworkAccessManager
    void onResult(QNetworkReply *reply);

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

#endif // WIDGET_H

widget.cpp

The process is to create QJsonDocument object and write the contents of QNetworkReply response. Then pick up the document root of the root object that contains all three properties. After that, pick up titles for their property values. From the second property "employes" pick up the array with the names and surnames of members of the Department. All data is placed in the ui->textEdit .

#include "widget.h"
#include "ui_widget.h"

#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>
#include <QUrlQuery>
#include <QNetworkReply>
#include <QUrl>

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

    networkManager = new QNetworkAccessManager();
    // Connect networkManager response to the handler
    connect(networkManager, &QNetworkAccessManager::finished, this, &Widget::onResult);
    // We get the data, namely JSON file from a site on a particular url
    networkManager->get(QNetworkRequest(QUrl("http://www.evileg.ru/it_example.json")));
}

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

void Widget::onResult(QNetworkReply *reply)
{
    // If there are no errors
    if(!reply->error()){

        // So create an object Json Document, by reading into it all the data from the response
        QJsonDocument document = QJsonDocument::fromJson(reply->readAll());

        // Taking from the document root object
        QJsonObject root = document.object();
        /* We find the object "departament", which is the very first in the root object.
         * Use the keys() method gets a list of all objects and the first index
         * Take away the name of the object on which we obtain its value
         * */
        ui->textEdit->append(root.keys().at(0) + ": " + root.value(root.keys().at(0)).toString());

        // The second value prescribe line
        QJsonValue jv = root.value("employees");
        // If the value is an array, ...
        if(jv.isArray()){
            // ... then pick from an array of properties
            QJsonArray ja = jv.toArray();
            // Going through all the elements of the array ...
            for(int i = 0; i < ja.count(); i++){
                QJsonObject subtree = ja.at(i).toObject();
                // Taking the values of the properties and last name by adding them to textEdit
                ui->textEdit->append(subtree.value("firstName").toString() +
                                     " " +
                                     subtree.value("lastName").toString());
            }
        }
        // At the end we take away the property of the number of employees of the department and also to output textEdit
        ui->textEdit->append(QString::number(root.value("number").toInt()));
    }
    reply->deleteLater();
}

Result

As a result of this code will have the following result, which is shown in the following image below.

Video

We recommend hosting TIMEWEB
We recommend hosting TIMEWEB
Stable hosting, on which the social network EVILEG is located. For projects on Django we recommend VDS hosting.

Do you like it? Share on social networks!

Comments

Only authorized users can post comments.
Please, Log in or Sign up
AD

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:50points,
  • Rating points-4
m

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:80points,
  • Rating points4
m

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:20points,
  • Rating points-10
Last comments
ИМ
Игорь МаксимовNov. 22, 2024, 11:51 a.m.
Django - Tutorial 017. Customize the login page to Django Добрый вечер Евгений! Я сделал себе авторизацию аналогичную вашей, все работает, кроме возврата к предидущей странице. Редеректит всегда на главную, хотя в логах сервера вижу запросы на правильн…
Evgenii Legotckoi
Evgenii LegotckoiOct. 31, 2024, 2:37 p.m.
Django - Lesson 064. How to write a Python Markdown extension Добрый день. Да, можно. Либо через такие же плагины, либо с постобработкой через python библиотеку Beautiful Soup
A
ALO1ZEOct. 19, 2024, 8:19 a.m.
Fb3 file reader on Qt Creator Подскажите как это запустить? Я не шарю в программировании и кодинге. Скачал и установаил Qt, но куча ошибок выдается и не запустить. А очень надо fb3 переконвертировать в html
ИМ
Игорь МаксимовOct. 5, 2024, 7:51 a.m.
Django - Lesson 064. How to write a Python Markdown extension Приветствую Евгений! У меня вопрос. Можно ли вставлять свои классы в разметку редактора markdown? Допустим имея стандартную разметку: <ul> <li></li> <li></l…
d
dblas5July 5, 2024, 11:02 a.m.
QML - Lesson 016. SQLite database and the working with it in QML Qt Здравствуйте, возникает такая проблема (я новичок): ApplicationWindow неизвестный элемент. (М300) для TextField и Button аналогично. Могу предположить, что из-за более новой верси…
Now discuss on the forum
m
moogoNov. 22, 2024, 7:17 a.m.
Mosquito Spray System Effective Mosquito Systems for Backyard | Eco-Friendly Misting Control Device & Repellent Spray - Moogo ; Upgrade your backyard with our mosquito-repellent device! Our misters conce…
Evgenii Legotckoi
Evgenii LegotckoiJune 24, 2024, 3:11 p.m.
добавить qlineseries в функции Я тут. Работы оень много. Отправил его в бан.
t
tonypeachey1Nov. 15, 2024, 6:04 a.m.
google domain [url=https://google.com/]domain[/url] domain [http://www.example.com link title]
NSProject
NSProjectJune 4, 2022, 3:49 a.m.
Всё ещё разбираюсь с кешем. В следствии прочтения данной статьи. Я принял для себя решение сделать кеширование свойств менеджера модели LikeDislike. И так как установка evileg_core для меня не была возможна, ибо он писался…

Follow us in social networks