CODEWITHSUNDEEP
c++qtqt5
inkms
inkms

Reputation: 41

QJsonDocument::fromJson cannot parse QJsonDocument::toJson QByteArray

I'm using QJsonDocument::toJson to convert a QJsonObject into a QByteArray, and somewhere else in the program, I read that QByteArray and convert it to a QJsonObject using QJsonDocument::fromJson. It doesn't work and I don't know why. QJsonParseError doesn't show anything.

How can I successfully convert to and from QByteArray <--> QJsonObject?

If I run:

QJsonDocument doc, doc2;
QJsonParseError jsonerror;
QJsonObject original, copy;

original.insert("foo", 1);
original.insert("bar",2);

doc.setObject(original);
doc2.fromJson(doc.toJson(), &jsonerror);
copy = doc2.object();

qDebug() << doc.toJson();
qDebug() << jsonerror.errorString();
qDebug() << "Null: " << doc2.isNull() << " Object: " << doc2.isObject() << " Array: " << doc2.isArray() << " Empty: " << doc2.isEmpty();
qDebug() << copy.size();

I get the following output:

"{\n "bar": 2,\n "foo": 1\n}\n"

"no error occurred"

Null: true Object: false Array: false Empty: true

0

I expected the object copy to contain the key-value pairs from original. It seems like fromJson is not managing to read the result of toJson.

I also tried using the format identifier in toJson to force it to be compact doc2.fromJson(doc.toJson(QJsonDocument::Compact), &jsonerror); and while the output is different, the resulting object is still empty

"{"bar":2,"foo":1}"

"no error occurred"

Null: true Object: false Array: false Empty: true

0

Upvotes: 1

Views: 293

Answers (1)

inkms
inkms

Reputation: 41

The method fromJson is a static member function, so calling doc2.fromJson(...) does not change anything inside doc2, instead it constructs a new QJsonDocument and as it has nowhere to go (it is not assigned to anything) it is lost.

This is the example above corrected:

QJsonDocument doc;
QJsonParseError jsonerror;
QJsonObject original, copy;

original.insert("foo", 1);
original.insert("bar",2);

doc.setObject(original);
QJsonDocument doc2 = QJsonDocument::fromJson(doc.toJson(), &jsonerror);
copy = doc2.object();

qDebug() << doc.toJson();
qDebug() << jsonerror.errorString();
qDebug() << "Null: " << doc2.isNull() << " Object: " << doc2.isObject() << " Array: " << doc2.isArray() << " Empty: " << doc2.isEmpty();
qDebug() << copy.size();

Which generates the output:

"{\n "bar": 2,\n "foo": 1\n}\n"

"no error occurred"

Null: false Object: true Array: false Empty: false

2

Upvotes: 3

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