Various entanglements between qvariant and Jason -- QT

Preface  

Although I knew QVariant Some of the features of , But not with Json All kinds of mutual transformation . I used to analyze Json after , Is to convert it into my customized structure , Convenient to see , It's easy to call , It is troublesome to parse and convert ; Later, I saw my colleagues directly Json Convert to QVariant（ or QVariantMap  QVariantList）, Then call directly , I think it's good , But there are some confused places in the middle , So write it down here .

All kinds of mutual transformation

First A word of warning , This is also a mistake I often make ： Don't think about one step ,QVariant What type of deposit , Just transfer it out of what type ！！！

Json To QVariant

QJsonObject To QVariant,QVariant The constructor of contains these types .

    QJsonObject obj;
    obj.insert("name1","val1");
    obj.insert("name2","val2");
    obj.insert("name3","val3");
    QJsonArray arr;
    for(int i=0;i<5;i++)
        arr.append(i);

    obj.insert("name4",arr);

    QVariant var(obj);

Of course ,QJsonArray To QVariant It's the same

QVariant var2(arr);

also ,QJsonDocument To QVariant

QVariant var3(QJsonDocument(obj));

  Generally, for the convenience of local call , Is to directly convert it into QVariantMap、QVariantHash or QVariantList

    QVariantList varList=arr.toVariantList();
    QVariantMap varMap=obj.toVariantMap();
    QVariantHash varHash=obj.toVariantHash();

When you use it , Call directly

    qDebug()<<"varName_1="<<varMap.value("name1").toString();
    qDebug()<<"varName_2="<<varHash.value("name2").toString();
    for(int i=0;i<varList.count();i++){
        qDebug()<<varList.at(i).toInt();
    }

QVariant To Json

This only needs direct conversion , Premise is QVariant Originally, the type of deposit is Json

 const QJsonObject& _obj=var.toJsonObject();

  If deposited QVariant The type is QVariantMap, Then one more step is needed

    QVariant var4(obj.toVariantMap());

    const QJsonObject& __obj=QJsonObject::fromVariantMap(var4.toMap());
    qDebug()<<__obj.value("name1").toString();

 

QVariant To QByteArray

Look at the help documentation , It can be seen that QVariant There are ways to directly convert into QByteArray, Just convert it directly into QByteArray, So what you got QByteArray It's probably empty ~

I still emphasize depositing QVariant What is the , You have to convert it directly to why , As for the other types , Continue to convert .

If deposited QVariant Yes. QJsonObject And so on

qDebug()<<QJsonDocument(var.toJsonObject()).toJson(QJsonDocument::Compact);

If the deposit is QVariant Yes. QVariantMap And so on

qDebug()<<QJsonDocument::fromVariant(var4).toJson();

If the deposit is QByteArray, So what to say , Of course, direct conversion , Of course , The result is not empty , Unless you store an empty byte array  

    QJsonDocument doc(obj);
    QVariant var5(doc.toJson(QJsonDocument::Compact));
    qDebug()<<var5.toByteArray();

 

Conclusion  

QVariant What is deposited in , Extracted , The type must correspond to ！！！！