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QT notes - qjason
2022-07-22 18:11:00 【Cool breeze in the old street °】
The header file ：
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>
#include <QJsonParseError>
#include <QJsonValue>
QJsonDocument Class for reading and writing JSON file .
QJsonArray Class encapsulates a JSON Array .
QJsonObject Class encapsulates a JSON object .
QJsonValue Class encapsulates a value .
QJsonParseError Class is used in JSON Error reported in parsing .
jsonObject The output order of and The insertion order is inconsistent
jsonArray The output order of and The insertion order is consistentjsonValue You can judge the type of value then What type of value to convert
1. ordinary jsonObject：
1.1 ordinary jsonObject output to a file
QJsonObject json;
json.insert("Name", "Qt");
json.insert("From", 1991);
json.insert("Cross Platform", true);
// structure JSON file
QJsonDocument document;
document.setObject(json);
byteArray2 = document.toJson(QJsonDocument::Compact);
QString strJson(byteArray2);
qDebug() << strJson;
1.2 Parse read jsonObject
QJsonParseError jsonError;
QJsonDocument document = QJsonDocument::fromJson(byteArray2, &jsonError);
if (!document.isNull() && jsonError.error == QJsonParseError::NoError)
{
// Is there an object
if (document.isObject())
{
// Is there a specified Key
QJsonObject object = document.object();
if (object.contains("Name"))
{
// Specified or not Value For the string
QJsonValue value = object.value("Name");
if (value.isString())
{
QString strName = value.toString();
qDebug() << "Name:" << strName;
}
}
if (object.contains("From"))
{
QJsonValue value = object.value("From");
if (value.isDouble())
{
int nFrom = value.toVariant().toInt();
qDebug() << "From:" << nFrom;
}
}
if (object.contains("Cross Platform"))
{
QJsonValue value = object.value("Cross Platform");
if (value.isBool())
{
bool bCrossPlatform = value.toBool();
qDebug() << "Platform:" << bCrossPlatform;
}
}
}
}
1.3 File output and code output 
2. ordinary jsonArray：
2.1 ordinary jsonArray output to a file
QJsonArray jsonArray;
jsonArray.append(8.17);
jsonArray.append(true);
jsonArray.append("lion_cxq");
QJsonDocument jsonDoc;
jsonDoc.setArray(jsonArray);
byteArray3 = jsonDoc.toJson(QJsonDocument::Compact);
qDebug() << QString(byteArray3);
2.2 Parse read jsonArray
QJsonParseError jsonError;
QJsonDocument jsonDoc = QJsonDocument::fromJson(byteArray3, &jsonError);
if (!jsonDoc.isNull() && jsonError.error == QJsonParseError::NoError)
{
if (jsonDoc.isArray())
{
QJsonArray jsonArray = jsonDoc.array();
int nSize = jsonArray.size();
for (int i = 0; i < nSize; i++)
{
QJsonValue value = jsonArray.at(i);
if (value.type() == QJsonValue::String)
{
QString strName = value.toString();
qDebug() << strName;
}
if (value.type() == QJsonValue::Double)
{
double dValue = value.toDouble();
qDebug() << dValue;
}
if (value.type() == QJsonValue::Bool)
{
bool bValue = value.toBool();
qDebug() << bValue;
}
}
}
}
2.3 File output and code output 
3.jsonArray and jsonObject combination ：
3.1jsonArray and jsonOject output to a file
QJsonObject page;
page.insert("Developers", "https://www.qt.io/developers/");
page.insert("Download", "https://www.qt.io/download/");
page.insert("Home", "https://www.qt.io/");
QJsonArray version;
version.append(4.8);
version.append(5.2);
version.append(5.7);
QJsonObject jsonObject;
jsonObject.insert("Company", "Digia");
jsonObject.insert("From", 1991);
jsonObject.insert("Name", "Qt");
jsonObject.insert("Page", QJsonValue(page));
jsonObject.insert("Version", QJsonValue(version));
QJsonDocument jsonDoc;
jsonDoc.setObject(jsonObject);
byteArray4 = jsonDoc.toJson();
qDebug() << QString(byteArray4);
3.2 Parse and read jsonArray and jsonOject
QJsonParseError jsonError;
QJsonDocument jsonDoc = QJsonDocument::fromJson(byteArray4, &jsonError);
if (!jsonDoc.isNull() && jsonError.error == QJsonParseError::NoError)
{
// Is there an object
if (jsonDoc.isObject())
{
// Corresponding Key Of alue value
QJsonObject jsonObject = jsonDoc.object();
if (jsonObject.contains("Company"))
{
QJsonValue jsonValue = jsonObject.value("Company");
if (jsonValue.isString())
{
QString strCompany = jsonValue.toString();
qDebug() << strCompany;
}
}
if (jsonObject.contains("From"))
{
QJsonValue jsonValue = jsonObject.value("From");
if (jsonValue.toDouble())
{
int iFrom = jsonValue.toInt();
qDebug() << iFrom;
}
}
if (jsonObject.contains("Name"))
{
QJsonValue jsonValue = jsonObject.value("Name");
if (jsonValue.isString())
{
QString strName = jsonValue.toString();
qDebug() << strName;
}
}
if (jsonObject.contains("Page"))
{
QJsonValue jsonValue = jsonObject.value("Page");
if (jsonValue.isObject())
{
QJsonObject jsonObject1 = jsonValue.toObject();
if (jsonObject1.contains("Developers"))
{
QJsonValue jsonValue1 = jsonObject1.value("Developers");
if (jsonValue1.isString())
{
QString strDevlopers = jsonValue1.toString();
qDebug() << strDevlopers;
}
}
if (jsonObject1.contains("Download"))
{
QJsonValue jsonValue1 = jsonObject1.value("Download");
if (jsonValue1.isString())
{
QString strDownload = jsonValue1.toString();
qDebug() << strDownload;
}
}
if (jsonObject1.contains("Home"))
{
QJsonValue jsonValue1 = jsonObject1.value("Home");
if (jsonValue1.isString())
{
QString strHome = jsonValue1.toString();
qDebug() << strHome;
}
}
}
}
if (jsonObject.contains("Version"))
{
QJsonValue jsonValue1 = jsonObject.value("Version");
if (jsonValue1.isArray())
{
QJsonArray jsonArray = jsonValue1.toArray();
int sizeArray = jsonArray.size();
for (int i = 0; i < sizeArray; ++i)
{
QJsonValue value = jsonArray.at(i);
if (value.isDouble())
{
double dValue = value.toDouble();
qDebug() << dValue;
}
}
}
}
}
}
3.3 File output And code output 
Complete code ：
#pragma once
#include <QtWidgets/QWidget>
#include "ui_QJsonArrayDifficultTest.h"
class QJsonArrayDifficultTest : public QWidget
{
Q_OBJECT
public:
QJsonArrayDifficultTest(QWidget *parent = Q_NULLPTR);
~QJsonArrayDifficultTest();
void QJsonArrayDifficultTest1();
void QJsonArrayDifficultTest2();
void resolutionArrayDifficultTest2();
void QJsonArrayDifficultTest3();
void resolutionArrayDifficultTest3();
void QJsonArrayDifficultTest4();
void resolutionArrayDifficultTest4();
private:
Ui::QJsonArrayDifficultTestClass ui;
QByteArray byteArray2;
QByteArray byteArray3;
QByteArray byteArray4;
};
#include "QJsonArrayDifficultTest.h"
#include <QFile>
#include <QDebug>
#include <QJsonArray>
#include <QJsonObject>
#include <QDateTime>
#include <QThread>
#include <QJsonDocument>
#include <QJsonParseError>
QJsonArrayDifficultTest::QJsonArrayDifficultTest(QWidget *parent)
: QWidget(parent)
{
ui.setupUi(this);
QJsonArrayDifficultTest1();
QJsonArrayDifficultTest2();
resolutionArrayDifficultTest2();
QJsonArrayDifficultTest3();
resolutionArrayDifficultTest3();
QJsonArrayDifficultTest4();
resolutionArrayDifficultTest4();
}
QJsonArrayDifficultTest::~QJsonArrayDifficultTest()
{
}
void QJsonArrayDifficultTest::QJsonArrayDifficultTest1()
{
QFile file("./jsonArrayDifficlutTset1.json");
if (file.open(QIODevice::ReadWrite))
qDebug() << "file open error";
else
qDebug() << "file open";
file.resize(0);
QJsonArray jsonArray;
for (int i = 0; i < 3; i++)
{
QJsonObject jsonObject;
jsonObject.insert("name", QString::number(i + 1));
jsonObject.insert("age", i + 18);
jsonObject.insert("time", QDateTime::currentDateTime().toString("yyyy-MM-dd hh-MM-ss"));
jsonArray.append(jsonObject);
}
QJsonObject jsonObject;
jsonObject.insert("number", jsonArray.size());
jsonArray.append(jsonObject);
QJsonDocument jsonDoc;
jsonDoc.setArray(jsonArray);
file.write(jsonDoc.toJson());
file.close();
qDebug() << "write to file";
if (jsonDoc.isArray())
qDebug() << QStringLiteral(" There are arrays ") << jsonDoc.array();
if (jsonDoc.isObject())
qDebug() << QStringLiteral(" There are objects ");
else
qDebug() << QStringLiteral(" No object ") << jsonDoc.object();
if (!jsonDoc.isNull())
qDebug() << QStringLiteral(" Not empty ") << jsonDoc.toJson(QJsonDocument::Compact);
if (!jsonDoc.isEmpty())
{
QByteArray byteArray = jsonDoc.toJson(QJsonDocument::Indented);
qDebug() << QStringLiteral(" Not empty ") << QString(byteArray);
}
}
void QJsonArrayDifficultTest::QJsonArrayDifficultTest2()
{
QFile file("./jsonArrayDifficlutTset2.json");
if (file.open(QIODevice::ReadWrite))
qDebug() << "file open error";
else
qDebug() << "file open";
file.resize(0);
QJsonObject json;
json.insert("Name", "Qt");
json.insert("From", 1991);
json.insert("Cross Platform", true);
QJsonDocument document;
document.setObject(json);
byteArray2 = document.toJson(QJsonDocument::Compact);
QString strJson(byteArray2);
qDebug() << strJson;
file.write(document.toJson());
file.close();
qDebug() << "write to file";
}
void QJsonArrayDifficultTest::resolutionArrayDifficultTest2()
{
QJsonParseError jsonError;
QJsonDocument document = QJsonDocument::fromJson(byteArray2, &jsonError);
if (!document.isNull() && jsonError.error == QJsonParseError::NoError)
{
if (document.isObject())
{
QJsonObject object = document.object();
if (object.contains("Name"))
{
QJsonValue value = object.value("Name");
if (value.isString())
{
QString strName = value.toString();
qDebug() << "Name:" << strName;
}
}
if (object.contains("From"))
{
QJsonValue value = object.value("From");
if (value.isDouble())
{
int nFrom = value.toVariant().toInt();
qDebug() << "From:" << nFrom;
}
}
if (object.contains("Cross Platform"))
{
QJsonValue value = object.value("Cross Platform");
if (value.isBool())
{
bool bCrossPlatform = value.toBool();
qDebug() << "Platform:" << bCrossPlatform;
}
}
}
}
}
void QJsonArrayDifficultTest::QJsonArrayDifficultTest3()
{
QFile file("./jsonArrayDifficlutTset3.json");
if (file.open(QIODevice::ReadWrite))
qDebug() << "file open error";
else
qDebug() << "file open";
file.resize(0);
QJsonArray jsonArray;
jsonArray.append(8.17);
jsonArray.append(true);
jsonArray.append("lion_cxq");
QJsonDocument jsonDoc;
jsonDoc.setArray(jsonArray);
byteArray3 = jsonDoc.toJson(QJsonDocument::Compact);
qDebug() << QString(byteArray3);
file.write(jsonDoc.toJson());
file.close();
qDebug() << "wirte finish";
}
void QJsonArrayDifficultTest::resolutionArrayDifficultTest3()
{
QJsonParseError jsonError;
QJsonDocument jsonDoc = QJsonDocument::fromJson(byteArray3, &jsonError);
if (!jsonDoc.isNull() && jsonError.error == QJsonParseError::NoError)
{
if (jsonDoc.isArray())
{
QJsonArray jsonArray = jsonDoc.array();
int nSize = jsonArray.size();
for (int i = 0; i < nSize; i++)
{
QJsonValue value = jsonArray.at(i);
if (value.type() == QJsonValue::String)
{
QString strName = value.toString();
qDebug() << strName;
}
if (value.type() == QJsonValue::Double)
{
double dValue = value.toDouble();
qDebug() << dValue;
}
if (value.type() == QJsonValue::Bool)
{
bool bValue = value.toBool();
qDebug() << bValue;
}
}
}
}
}
void QJsonArrayDifficultTest::QJsonArrayDifficultTest4()
{
QFile file("./jsonArrayDifficultTest4.json");
if (file.open(QIODevice::ReadWrite))
{
qDebug() << "wirte read json file";
}
else
{
qDebug() << "qita file";
return;
}
file.resize(0);
QJsonObject page;
page.insert("Developers", "https://www.qt.io/developers/");
page.insert("Download", "https://www.qt.io/download/");
page.insert("Home", "https://www.qt.io/");
QJsonArray version;
version.append(4.8);
version.append(5.2);
version.append(5.7);
QJsonObject jsonObject;
jsonObject.insert("Company", "Digia");
jsonObject.insert("From", 1991);
jsonObject.insert("Name", "Qt");
jsonObject.insert("Page", QJsonValue(page));
jsonObject.insert("Version", QJsonValue(version));
QJsonDocument jsonDoc;
jsonDoc.setObject(jsonObject);
byteArray4 = jsonDoc.toJson();
qDebug() << QString(byteArray4);
file.write(jsonDoc.toJson());
file.close();
qDebug() << "write file";
}
void QJsonArrayDifficultTest::resolutionArrayDifficultTest4()
{
QJsonParseError jsonError;
QJsonDocument jsonDoc = QJsonDocument::fromJson(byteArray4, &jsonError);
if (!jsonDoc.isNull() && jsonError.error == QJsonParseError::NoError)
{
// Is there an object
if (jsonDoc.isObject())
{
// Corresponding Key Of alue value
QJsonObject jsonObject = jsonDoc.object();
if (jsonObject.contains("Company"))
{
QJsonValue jsonValue = jsonObject.value("Company");
if (jsonValue.isString())
{
QString strCompany = jsonValue.toString();
qDebug() << strCompany;
}
}
if (jsonObject.contains("From"))
{
QJsonValue jsonValue = jsonObject.value("From");
if (jsonValue.toDouble())
{
int iFrom = jsonValue.toInt();
qDebug() << iFrom;
}
}
if (jsonObject.contains("Name"))
{
QJsonValue jsonValue = jsonObject.value("Name");
if (jsonValue.isString())
{
QString strName = jsonValue.toString();
qDebug() << strName;
}
}
if (jsonObject.contains("Page"))
{
QJsonValue jsonValue = jsonObject.value("Page");
if (jsonValue.isObject())
{
QJsonObject jsonObject1 = jsonValue.toObject();
if (jsonObject1.contains("Developers"))
{
QJsonValue jsonValue1 = jsonObject1.value("Developers");
if (jsonValue1.isString())
{
QString strDevlopers = jsonValue1.toString();
qDebug() << strDevlopers;
}
}
if (jsonObject1.contains("Download"))
{
QJsonValue jsonValue1 = jsonObject1.value("Download");
if (jsonValue1.isString())
{
QString strDownload = jsonValue1.toString();
qDebug() << strDownload;
}
}
if (jsonObject1.contains("Home"))
{
QJsonValue jsonValue1 = jsonObject1.value("Home");
if (jsonValue1.isString())
{
QString strHome = jsonValue1.toString();
qDebug() << strHome;
}
}
}
}
if (jsonObject.contains("Version"))
{
QJsonValue jsonValue1 = jsonObject.value("Version");
if (jsonValue1.isArray())
{
QJsonArray jsonArray = jsonValue1.toArray();
int sizeArray = jsonArray.size();
for (int i = 0; i < sizeArray; ++i)
{
QJsonValue value = jsonArray.at(i);
if (value.isDouble())
{
double dValue = value.toDouble();
qDebug() << dValue;
}
}
}
}
}
}
}
Reference blog ：
https://www.21ic.com/tougao/article/11375.html
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