Use Json data in Qt in Windows

Negar_mg

sorry,I wanted to use Json

eyllanesc

@Negar_mg See https://doc.qt.io/qt-5/qjsondocument.html

Negar_mg

thank you,you are the best.

JonB

@Negar_mg said in Use Json data in Qt in Windows:

How do I add Json to qt_creator?

That doesn't exist, Creator itself neither cares nor knows about JSON. Designer does not use it. You may use JSON in code you happen to write in Creator's code editor, but it's nothing to do with Creator. Just so you know.

Negar_mg

@JonB
Thanks , can I use QJsonDocument Class to read json from serial port?
Is it possible to read and write this data in qt or c ++ libraries?

JonB

@Negar_mg
As you can read at https://doc.qt.io/qt-5/qjsondocument.html#details

QJsonDocument is a class that wraps a complete JSON document and can read and write this document both from a UTF-8 encoded text based representation as well as Qt's own binary format.

Since you will use QJsonDocument QJsonDocument::fromJson(const QByteArray &json, QJsonParseError *error = nullptr) you will need a QByteArray. It does not do the reading, you will need to fetch the bytes from the serial port.

Is it possible to read and write this data in qt or c ++ libraries?

Read and write what data? Serial port? Yes. JSON? Yes.

Negar_mg

@JonB
Thanks for the explanation. I'm trying it now
I just had one more question, should I use QSerialPort Class to fetch Json data from the serial port?

JonB

@Negar_mg
Yes that's fine. Try to separate serial data and JSON data in your head. Serial data is just bytes, it could be anything. JSON is treat bytes as text and parse it as JSON. Two unconnected things, you can put them together if it suits you.

Negar_mg

@JonB
thanks alot

Negar_mg

I used the following code and was able to get Json data from the serial port.
But the data is displayed as I sent it to you in the image, how can I separate it and store each in a different variable?

   serial.setPortName("COM3");
   serial.open(QIODevice::ReadWrite);
   serial.setBaudRate(QSerialPort::Baud9600);
   serial.setDataBits(QSerialPort::Data8);
   serial.setParity(QSerialPort::NoParity);
   serial.setStopBits(QSerialPort::OneStop);
   serial.setFlowControl(QSerialPort::NoFlowControl);
    while(!serial.isOpen()) serial.open(QIODevice::ReadWrite);

   if (serial.isOpen() && serial.isWritable())
   {
   qDebug() << "Serial is open";

   QByteArray output;
   QByteArray input;

     while(true)
     {
     output = "a";
     serial.write(output);
    serial.flush();

     serial.waitForBytesWritten(1000);
     serial.waitForReadyRead(1000);

     input = serial.readAll();
     qDebug()<<input;


     }


   }

The data should be as follows, but as you can see in the first image, the data is not readable

Christian Ehrlicher

I don't see a difference between those two pictures. The json content is exactly the same. If you want to parse the json you should take a look at the documentation of QJsonDocument and it's corresponding classes.

Negar_mg

@Christian-Ehrlicher
Thanks, how can I separate the data? I do not know how to use QJsonDocument?
Can you guide me with an example? For example, what should I do to store the amount of Bat_Temp data in the x variable?

mrjj

@Negar_mg said in Use Json data in Qt in Windows:

QJsonDocument

   QString input = "{Bat_temp:19}"; // you used a picture so could not get real input
  // the toUTF is due to it wants a bytearrya not qstring. 
   QJsonDocument jsonResponse = QJsonDocument::fromJson(input.toUtf8());
  // ask for a json object
    QJsonObject jsonObject = jsonResponse.object();
  //access a property of that json object
    int value = jsonObject["Bat_temp"].toInt();

for dht11Data you must use QJsonArray

Negar_mg

@mrjj
thank you

_-mohamed-_

@Negar_mg this is the best example, it helped me a lot:
Example of how to use JSON file with QT

Negar_mg

@_-mohamed-_
thanks a lot
You know, my problem is that I receive data from the Arduino from the serial port
As I wrote in the above code, I can print data with an infinite loop.
As follows :

            while (true)
            {
            serial.waitForReadyRead (100000);
            input = input.append (serial.readAll ());
            qDebug () << input;
            }

And the output is as follows:

//..............................................................................................................................
Serial is open
"{"
"{" dht "
"{" dht11Da "
"{" dht11Data \ ":"
"{" dht11Data \ ": [29,"
"{" dht11Data \ ": [29,27]}"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " "
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht1 "
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Da "
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ":"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n]"
"{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n] \ r \ n } "
//..........................................................................................................................................
No data is received at first, so I do not know how to manage this infinite loop and store the data in an array

_-mohamed-_

@Negar_mg do you mean that you want to save the final result in a json file?

Negar_mg

@_-mohamed-_
i want to save this {" dht11Data \ ": [29,27]}
And I want to display each of the numbers like 27 in one lineEdit.

_-mohamed-_

@Negar_mg You can't use a backslash in the key, you can use FrontSlash instead

This is the code you need:

#include <QApplication>
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>
#include <QByteArray>
#include <QJsonValue>
#include <QDebug>
#include <QFile>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QFile file("C:/Users/moham/OneDrive/Desktop/json file.json"); //write the file path here

    if(!file.open(QFile::ReadOnly))    //opening file
        qDebug() << "can't open the file";

    else
    {
        QByteArray fileContents = file.readAll(); // reading the file
        file.close();   //closing file

        QJsonDocument jsonDoc = QJsonDocument::fromJson(fileContents);

        QJsonObject jsonObj = jsonDoc.object();

        QJsonArray jsonArray = jsonObj[" dht11Data / "].toArray();

        foreach(QJsonValue v, jsonArray)  //printing array's values
            qDebug() << v.toInt();        //

        return 0;
    }

    return a.exec();
}

this code reads (JSON file.json) and prints it in the console, you can use the values wherever you want.

I hope I helped you.

jsulm

@Negar_mg said in Use Json data in Qt in Windows:

infinite loop

Stop using infinite loops first!
Please take a look at documentation and examples to see how to properly use QSerialPort: https://doc.qt.io/qt-5/qtserialport-creaderasync-example.html
To read from serial port connect a slot to https://doc.qt.io/qt-5/qiodevice.html#readyRead signal and use readAll() in this slot. Keep in mind that you have to accumulate the data read from serial port until you got whole JSON document!