Полагаю, это может помочь и кому-то еще, я все понял, спасибо @Botje за его пример, который действительно помог. В общем, мне легко запомнить представление данных как QByteArray в памяти.
Минимальный пример для доступа, а также для использования каждого отдельного значения, хранящегося в файле json, вы можете:
(Да, я мог бы написать это еще более компактно, но, думаю, это облегчает понимание, поэтому я позаботился о функциях / классах / структурах ради удобства чтения.)
#include <QCoreApplication>
#include <QString>
#include <QVariant>
#include <QFile>
#include <QByteArray>
#include <QTextStream>
#include <QDebug>
//json specific
#include <QJsonParseError>
#include <QJsonDocument>
#include <QJsonArray>
#include <QJsonObject>
#include <QJsonParseError>
#include <QJsonValue>
void writeJsonFile();
void readJsonFile();
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
writeJsonFile();
readJsonFile();
return a.exec();
}
void writeJsonFile()
{
qDebug() << "Write Json File: ";
//1. Create a QJsonObject and add values to it
QJsonObject jsonObj;
jsonObj["FirstName"] = "John";
//no value will be written as null in the json file
jsonObj["MiddleName"];
jsonObj["LastName"] = "Doe";
jsonObj["Age"] = 43;
//2. Create Item of Json Object content (object of object)
QJsonObject jsonItemObj;
jsonItemObj["Street"] = "Downing Street 10";
jsonItemObj["City"] = "London";
jsonItemObj["Country"] = "Great Britain";
//3. Add jsonItemObj to jsonObj and give it an object Name
jsonObj["Address"] = jsonItemObj;
//4. Create jsonArray and fill it with values - similar to filling a vector
QJsonArray jsonArray;
jsonArray.append("+44 1234567");
jsonArray.append("+44 2345678");
//Add a bool to the Object
jsonObj["Valid"] = true;
//5. Add jsonArray to jsonObj and give it an object Name
jsonObj["Phone numbers"] = jsonArray;
//(It can also be added to the jsonItemObj to be inline with the Address section)
//with jsonItemObj["Phone numbers"] = jsonArray or as much objects of objects
//you need
/* As I understood it, most Qt classes use a QByteArray to handle data internally
* because it is really fast/efficient,
* also QFile QIODevice, it is a good idea to hold the read/write
* QIODevice data as QByteArray in the Memory
*/
//6. Create a QByteArray and fill it with QJsonDocument (json formatted)
QByteArray byteArray;
byteArray = QJsonDocument(jsonObj).toJson();
//7. Open a QFile and write the byteArray filled with json formatted data
//thanks to the QJsonDocument() Class to the file
QFile file;
file.setFileName("file.json");
if(!file.open(QIODevice::WriteOnly)){
qDebug() << "No write access for json file";
return;
}
//8. finally write the file and close it
file.write(byteArray);
file.close();
//9. Print out the byteArray to the terminal
QTextStream textStream(stdout);
textStream << "Rendered json byteArray text: " << endl;
textStream << byteArray << endl;
}
void readJsonFile()
{
qDebug() << "Read Json File:";
//1. Open the QFile and write it to a byteArray and close the file
QFile file;
file.setFileName("file.json");
if(!file.open(QIODevice::ReadOnly)){
qDebug() << "Json filef couldn't be opened/found";
return;
}
QByteArray byteArray;
byteArray = file.readAll();
file.close();
//2. Format the content of the byteArray as QJsonDocument
//and check on parse Errors
QJsonParseError parseError;
QJsonDocument jsonDoc;
jsonDoc = QJsonDocument::fromJson(byteArray, &parseError);
if(parseError.error != QJsonParseError::NoError){
qWarning() << "Parse error at " << parseError.offset << ":" << parseError.errorString();
return;
}
//3. Create a jsonObject and fill it with the byteArray content, formatted
//and holding by the jsonDocument Class
QJsonObject jsonObj;
jsonObj = jsonDoc.object();
//4. Now picking the jsonValues and printing them out or do what ever you need
QJsonValue jsonVal;
QTextStream textStream(stdout);
jsonVal = jsonObj.value("FirstName");
textStream << jsonVal.toString() << endl;
jsonVal = jsonObj.value("MiddleName");
//null gets back to an empty fild - added the sting "null/empty" to make it visible
textStream << jsonVal.toVariant().toString() << "null/empty" << endl;
jsonVal = jsonObj.value("LastName");
textStream << jsonVal.toString() << endl;
//The number has to be converted to an int and than to a string to print it
jsonVal = jsonObj.value("Age");
textStream << QString::number(jsonVal.toInt()) << endl;
//5. Now we need to fill the object of the object. To do that, we need
//the Item Object and a jsonSubVal object for json without a loop
QJsonObject jsonItemObj;
QJsonValue jsonSubVal;
jsonVal = jsonObj.value(QString("Address"));
jsonItemObj = jsonVal.toObject();
jsonSubVal = jsonItemObj["Street"];
textStream << jsonSubVal.toString() << endl;
jsonSubVal = jsonItemObj["City"];
textStream << jsonSubVal.toString() << endl;
jsonSubVal = jsonItemObj["Country"];
textStream << jsonSubVal.toString() << endl;
//6. now the Phone Numbers array with a loop
QJsonArray jsonArray;
jsonArray = jsonObj["Phone numbers"].toArray();
for(int i = 0; i < jsonArray.size(); i++)
textStream << jsonArray[i].toString() << endl;
textStream << "or with foreach" << endl;
foreach(QJsonValue v, jsonArray)
textStream << v.toString() << endl;
//7. And finally the bool value:
jsonVal = jsonObj.value(QString("Valid"));
textStream << jsonVal.toVariant().toString() << endl;
textStream << "or as number, not a string: ";
textStream << (QString::number(jsonVal.toInt())) << endl;
textStream << "\nThe whole file as printed in the file \n" <<
jsonDoc.toJson(QJsonDocument::Indented);
