How to get a Json value from an api and display it in a GUI

hoonara

Good day,

I'm tring to make a GUI that processes an api requested value. Those values are in Json format.

https://api.bitmart.com/ticker/BMX_ETH

Let's say I want to get the value of "bid_1" and make a pushbutton and a lable that changes into the value of "bid_1" when clicked.

To make a simple onpushbuttonclicked I use this

void MainWindow::on_pushButton_clicked()
{
    ui->label_11->setText("Hello");
}

Instead of "hello" I want a String with the value of "bid_1".

As far as I understand I have to use

void MainWindow::on_pushButton_clicked()
{
    QUrl url("https://api.bitmart.com/ticker/BMX_ETH");
    QNetworkRequest request(url);
    //send request
    //read replied data
    //interpret replied data as string/Json
    ui->label->setText(QString::number);
}

But I don't understand and would like to know how to send the request for a specific json value and convert it into a string. I appreciate any help with the given example so I can transfer its solution to my project.

SGaist

Hi and welcome to devnet,

Please take a look at QNetworkAccessManager and QJsonDocument.

You can load the answer you get for your request in a QJsonDocument and then parse it for what you are interested in and update your UI accordingly.

mrjj

@hoonara said in How to get a Json value from an api and display it in a GUI:

https://api.bitmart.com/ticker/BMX_ETH

Returns a full json object. Its doubtful it supports asking for one key/value.

You are supposed to read all of it and parse it and extra the values you want.

{
  "priceChange":"2.38%",
  "symbolId":22,
  "website":"https://www.bitmart.com/trade.html?symbol=22",
  "depthEndPrecision":6,
  "ask_1":"0.000308",
  "anchorId":16,
  "anchorName":"ETH",
  "pair":"BMX_ETH",
  "volume":"7684655.420000",
  "coinId":18,
  "depthStartPrecision":4,
  "high_24h":"0.000315",
  "low_24h":"0.000290",
  "new_24h":"0.000301",
  "closeTime":1528145084775,
  "bid_1":"0.000294",
  "coinName":"BMX",
  "baseVolume":"2341.535069",
  "openTime":1528058684775
}

Since its not a nested it should be very easy.

mrjj

Hi
fast sample.
it need error handling to be useful in real code ! ( dont skip that if for a real program)

#include <QApplication>
#include <QDebug>
#include <QJsonDocument>
#include <QJsonObject>
#include <QNetworkReply>
#include <QNetworkAccessManager>

int main(int argc, char* argv[]) {
  QApplication a(argc, argv);
  MainWindow w;
  w.show();
 // if in mainwindow. make sure m_manager lives in .h as member. else it wont work. ( death by scope)
  QNetworkAccessManager m_manager; 
// make request 
 QNetworkRequest request = QNetworkRequest(QUrl("https://api.bitmart.com/ticker/BMX_ETH"));
  QNetworkReply* reply = m_manager.get(request);
  // connect to signal  when its done using lambda)
  QObject::connect(reply, &QNetworkReply::finished, [reply]() {
    // read data
    QString ReplyText = reply->readAll();
    // qDebug() << ReplyText;
    // ask doc to parse it
    QJsonDocument doc = QJsonDocument::fromJson(ReplyText.toUtf8());
    // we know first element in file is object, to try to ask for such
    QJsonObject obj = doc.object();
    // ask object for value
    QJsonValue value = obj.value(QString("bid_1"));
    qDebug() << "Bid value is" << value.toString();;
    reply->deleteLater(); // make sure to clean up
  });
  return a.exec();
}

and it outputs
Bid value is "0.000290"

Lodhi.bhkr

@mrjj : hi i have developed this code to get request reply in qt . But now I need a help to develop another qt application which respond to this get request

jsulm

@Lodhi-bhkr What is your question/problem?

Lodhi.bhkr

@jsulm : I need to develop a rest api like java supports a http request mapping in spring boot which give a json response to the request I send from this code. A Rest API is like when I request to the url with json data , my rest api will respond like another json response according to the request.

jsulm

@Lodhi-bhkr Sorry, but this is not a question. What did you try? What problems do you have? Please ask more specific questions.
Looks like you asked here already: https://forum.qt.io/topic/120439/qt-code-to-send-data-on-postman-http-post-request