Qt5 利用QJson从文件读取Json并解析

Json文件是这样：

{
	"first fruit":
	{
		"describe":"an apple",
		"icon":"appleIcon",
		"name":"apple"
	},
	"second fruit":
	{
		"describe":"an orange",
		"icon":"orangeIcon",
		"name":"orange"
	},
	"three fruit array":
	[
		"eat 0",
		"eat 1",
		"eat 2",
		"eat 3",
		"eat 4"
	]
}

存放在本地磁盘。
利用QJson可以方便的进行解析。

   QFile loadFile("D:\\1.json");

    if(!loadFile.open(QIODevice::ReadOnly))
    {
        qDebug() << "could't open projects json";
        return;
    }

    QByteArray allData = loadFile.readAll();
    loadFile.close();

    QJsonParseError jsonError;
    QJsonDocument jsonDoc(QJsonDocument::fromJson(allData, &jsonError));

    if(jsonError.error != QJsonParseError::NoError)
    {
        qDebug() << "json error!" << jsonError.errorString();
        return;
    }

    QJsonObject rootObj = jsonDoc.object();

    QStringList keys = rootObj.keys();
    for(int i = 0; i < keys.size(); i++)
    {
        qDebug() << "key" << i << " is:" << keys.at(i);
    }

    //因为是预先定义好的JSON数据格式，所以这里可以这样读取
    if(rootObj.contains("first fruit"))
    {
       QJsonObject subObj = rootObj.value("first fruit").toObject();
       qDebug() << "describe is:" << subObj["describe"].toString();
       qDebug() << "icon is:" << subObj["icon"].toString();
       qDebug() << "name is:" << subObj["name"].toString();
    }

    if(rootObj.contains("second fruit"))
    {
       QJsonObject subObj = rootObj.value("second fruit").toObject();
       qDebug() << "describe is:" << subObj.value("describe").toString();
       qDebug() << "icon is:" << subObj.value("icon").toString();
       qDebug() << "name is:" << subObj.value("name").toString();
    }

    if(rootObj.contains("three fruit array"))
    {
       QJsonArray subArray = rootObj.value("three fruit array").toArray();
       for(int i = 0; i< subArray.size(); i++)
       {
           qDebug() << i<<" value is:" << subArray.at(i).toString();
       }
    }

需要包含的头文件：

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

运行结果：

key 0  is: "first fruit"
key 1  is: "second fruit"
key 2  is: "three fruit array"
describe is: "an apple"
icon is: "appleIcon"
name is: "apple"
describe is: "an orange"
icon is: "orangeIcon"
name is: "orange"
0  value is: "eat 0"
1  value is: "eat 1"
2  value is: "eat 2"
3  value is: "eat 3"
4  value is: "eat 4"

Qt官方文档JSON Save Game Example
也可以看：JSON实战之savegame(Qt Example)

每次读取之前，都要判断

 void Character::read(const QJsonObject &json)
  {
      if (json.contains("name") && json["name"].isString())
          mName = json["name"].toString();

      if (json.contains("level") && json["level"].isDouble())
          mLevel = json["level"].toInt();

      if (json.contains("classType") && json["classType"].isDouble())
          mClassType = ClassType(json["classType"].toInt());
  }

先用contains判断是否存在，再用isString判断是能转换。

bool isArray() const
bool isBool() const
bool isDouble() const
bool isNull() const
bool isObject() const
bool isString() const
bool isUndefined() const

修改后的代码为：

	QFile loadFile("D:\\1.json");

    if(!loadFile.open(QIODevice::ReadOnly))
    {
        qDebug() << "could't open projects json";
        return;
    }

    QByteArray allData = loadFile.readAll();
    loadFile.close();

    QJsonParseError json_error;
    QJsonDocument jsonDoc(QJsonDocument::fromJson(allData, &json_error));

    if(json_error.error != QJsonParseError::NoError)
    {
        qDebug() << "json error!";
        return;
    }

    QJsonObject rootObj = jsonDoc.object();

    QStringList keys = rootObj.keys();
    for(int i = 0; i < keys.size(); i++)
    {
        qDebug() << "key" << i << " is:" << keys.at(i);
    }

    //因为是预先定义好的JSON数据格式，所以这里可以这样读取
    if(rootObj.contains("first fruit") && rootObj["first fruit"].isObject())
    {
        QJsonObject subObj = rootObj["first fruit"].toObject();
        if (subObj.contains("describe") && subObj["describe"].isString())
        {
            qDebug() << "describe is:" << subObj["describe"].toString();
        }
        if (subObj.contains("icon") && subObj["icon"].isString())
        {
            qDebug() << "icon is:" << subObj["icon"].toString();
        }
        if (subObj.contains("name") && subObj["name"].isString())
        {
            qDebug() << "name is:" << subObj["name"].toString();
        }
    }

    if(rootObj.contains("second fruit") && rootObj["second fruit"].isObject())
    {
        QJsonObject subObj = rootObj["second fruit"].toObject();
        if (subObj.contains("describe") && subObj["describe"].isString())
        {
            qDebug() << "describe is:" << subObj["describe"].toString();
        }
        if (subObj.contains("icon") && subObj["icon"].isString())
        {
            qDebug() << "icon is:" << subObj["icon"].toString();
        }
        if (subObj.contains("name") && subObj["name"].isString())
        {
            qDebug() << "name is:" << subObj["name"].toString();
        }
    }

    if(rootObj.contains("three fruit array") && rootObj["three fruit array"].isArray())
    {
        QJsonArray subArray = rootObj.value("three fruit array").toArray();
        for(int i = 0; i< subArray.size(); i++)
        {
            if (subArray[i].isString())
            {
                qDebug() << i<<" value is:" << subArray.at(i).toString();
            }
        }
    }