Work with json format

gen1izh

Hello!
Can you give me some examples for read\write json?
I can not understand how it work in qt.

For example

"[ { "Name" : "Bob", "Phonenumber" : 123 },
   { "Name" : "Alice", "Phonenumber" : 321 } ]"

How create and how read it after?

Thanks

SGaist

Hi,

What exactly is your problem ?

Did you already took a look a the JSON Save Game example ?

mrjj

Hi
I assumed you know json and seen the docs?
http://www.json.org/
So you know we got array and objects ?
Those map directly to QJsonArray and QJsonObject
So to use it we construct class and set properties and add to lists.
Your samle is
An Array with 2 objects.
So this is how it works as mini sample.
Note that for production code, you need more error checking. :)

#include <QJsonObject>
#include <QJsonArray>
#include <QJsonDocument>
#include <QDebug>
#include <QFile>

QJsonDocument loadJson(QString fileName) {
  QFile jsonFile(fileName);
  jsonFile.open(QFile::ReadOnly); // error checking!
  return QJsonDocument().fromJson(jsonFile.readAll());
}

void saveJson(QJsonDocument document, QString fileName) {
  QFile jsonFile(fileName);
  jsonFile.open(QFile::WriteOnly); // error checking!
  jsonFile.write(document.toJson());
}
// helper function to create a Person JSON Object
QJsonObject Person(QString Name, QString Phone ) {
  QJsonObject p;
  p["name"] = Name;
  p["phonenumber"] = Phone;
  return p;
}

void testCreateJSON() {
  // the first element in a json file must be Object or Array. Called the root.
  QJsonArray root;  // we use array as ur sample has array as "root"
  // now add some object to the list. the << adds to the list. you can also use append.
  root << Person("bob", "12121212") << Person("lisa", "9022020202");
  // now make a document and add the root object to it. Note that this is by copy and hence we do it last!
  QJsonDocument doc(root);
  // save it to file. Change path.
  saveJson(doc, "e:/test.json");
  // show
  qDebug() << doc.toJson();
}

void testReadJSON() {
  // make a doc
  QJsonDocument doc;
  // read it
  doc = loadJson("e:/test.json");

  // now we need to parse it. It can start with Object or array.
  // we know we start with array so we consider it error if object. ( in this case)
  //
  if( ! doc.isArray() ) {
    qDebug() << "File starts with object!" ;
    return;
  }

  // get the root array into arrayobj
  QJsonArray rootArray = doc.array();
  // loop over array
  for(const QJsonValue& val : rootArray) {
    // everything in list and properties is QJsonValue and u must converto to right type
    // we have objects in list
    QJsonObject loopObj = val.toObject();
    // it could also be toInt etc for other types than string
    qDebug() << loopObj["name"].toString();
    qDebug() << loopObj["phonenumber"].toString();
  }

}