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

JSON, QJsonArray, QJsonDocument, QJsonObject, QJsonValue, QNetworkAccessManager

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

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TT
June 13, 2019, 7:01 p.m.
Taimoor Tanweer

C++ - Test 001. The first program and data types

  • Result:66points,
  • Rating points-1
TT
June 13, 2019, 6:51 p.m.
Taimoor Tanweer

C++ - Test 002. Constants

  • Result:75points,
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ВМ
June 13, 2019, 12:30 p.m.
Ваня Мороз

C++ - Test 001. The first program and data types

  • Result:100points,
  • Rating points10
Last comments
i
June 17, 2019, 6:10 a.m.
ingenfly

Только по осям xAxis2, уAxis2 значения начинаются с 0. Почему-то xAxis2 и xAxis не синхронизированы по данным. Ну и QCustomPlot последний.
June 16, 2019, 8:21 p.m.
Евгений Легоцкой

Добрый день. Ну точно также добавляете ту же самую информацию на ось xAxis2, только добавляете другое форматирование customPlot->xAxis2->setDateTimeFormat("hh:mm"); если я ...
EF
June 14, 2019, 1:56 p.m.
Egor Fomin

Спасибо за ваш ответ, у меня получилось реализовать это. Тем не менее появилась другая проблема, поэтому опять надеюсь на вашу помощь. Скажем, я уже выставил точки и они соеденены. Когда я нач...
d
June 13, 2019, 2:47 p.m.
damix

Можно классу, который описывает точку, добавить сигнал, который подавать (emit), когда точка перемещается (переопределить mouseMoveEvent или mouseReleaseEvent). Так вот эти сигналы у каждой из...
i
June 13, 2019, 2:09 p.m.
ingenfly

Здравствайте! Подскажите, пожалуйста: customPlot->xAxis2->setTickLabels(true); //Здесь включается отображение данных на оси xAxis2. а можно как-то продублировать информацию cus...
Now discuss on the forum
June 20, 2019, 9:30 a.m.
IscanderChe

Вернулся к этой задачке только-только, поэтому и не ответил ничего раньше.Как переопределить mouseReleaseEvent(QMouseEvent* event) у QTableView, если QTableView задан в ui? Или задавать QTabl...
I
June 19, 2019, 1:41 p.m.
Intruder

Всем добрый день. При разборе XML файла наткнулся на тег вот такого плана: <TagName attribute1="value1" attribute2="value2" /> При попытке проверить на наличие такого элеме...
June 19, 2019, 12:55 p.m.
Михаиллл

Скажите пожалуйста, как его в таком случае перемещать и удалять?
June 18, 2019, 7:50 p.m.
Дмитрий

Большое спасибо! SDK заработал.К сожалению удалось продвинутся только на один шаг. При сборке чистого проекта NDK выдаёт следующие ошибки C:\Android\ndk-bundle/toolchains/arm-linux-andr...
June 18, 2019, 4:59 p.m.
Михаиллл

Добрый день.В этом учебнике представлен код INSTALLED_APPS = ( ... 'rest_framework', 'snippets.apps.SnippetsConfig',) На строчке 'snippets.apps.SnippetsConf...
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