I'm trying to parse this JSON Web-API using Qt5 and C++ using QJsonDocument and QJsonObject as seen here. But I fail to access the JSON value of the QJsonObject.
This is what I've tried so far:
// Contains the whole API as QString...
QString data = QString(reply->readAll());
// Reads the JSON as QJsonDocument...
QJsonDocument jsonResponse = QJsonDocument::fromJson(data.toUtf8());
// Reads the JSON as QJsonObject...
QJsonObject jsonObject = jsonResponse.object();
Now I have my object well prepared, but trying to access the values of the JSON somehow fails:
// This returns an empty string ""!?!
qDebug() << jsonObject.value("success").toString();
Well, maybe I got the keys wrong:
// Let's check the keys...
QStringList stringList = jsonObject.keys();
for (QStringList::Iterator it = stringList.begin(); it != stringList.end(); ++it)
{
// This returns "success" and "return" - huh!?!
qDebug() << *it;
}
OK, the keys are veryfied, why is it not working?
// Let's check the values by using the keys directly...
for (QStringList::Iterator it = stringList.begin(); it != stringList.end(); ++it)
{
// This returns empty strings "" and "" - now what?!?
qDebug() << jsonObject.value(*it).toString();
}
This again, makes no sense at all. I can't see why I can not access the value of the JSON object by the keys. Any idea?
I tried exactly the same code on other JSON APIs (for example this one) without any issues. I am totally stuck here.
Here's my solution for Qt5 Json parsing the Cryptsy API.
QEventLoop loopEvent;
QNetworkAccessManager namMNGR;
QObject::connect(&namMNGR, SIGNAL(finished(QNetworkReply*)), &loopEvent, SLOT(quit()));
QNetworkRequest req(QUrl(QString("http://pubapi.cryptsy.com/api.php?method=singlemarketdata&marketid=%1").arg(marketID)));
QNetworkReply *reply = namMNGR.get(req);
loopEvent.exec();
//Json API parsing begins.
QString jsonSTR = reply->readAll();
if (!(reply->error() == QNetworkReply::NoError)) {
delete reply; //API Connection Problem.
}
QJsonDocument jsonDocument = QJsonDocument::fromJson(jsonSTR.toUtf8());
QJsonObject obj1 = jsonDocument.object();
QJsonValue val1 = obj1.value(obj1.keys().first());
QJsonObject obj2 = val1.toObject();
QJsonValue val2 = obj2.value(obj2.keys().first());
QJsonObject obj3 = val2.toObject();
QJsonValue marketDataValue = obj3.value(obj3.keys().first());
QJsonObject marketDataObject = marketDataValue.toObject();
QJsonArray sellordersArray = marketDataObject["sellorders"].toArray();
Have you managed to get Authenticated POST API data from Qt5? I'm trying to figure out how to do it.
Related
I'm new to QT and I would like some help. If any of you could help me I would really appreciate it.
QUESTION:
I have an asynchronous class that makes an HTTP request and it's going to receive some data into a JSON format and from there I will extract the necessary information which should be passed to my custom widget. How can I do that? Because I don't know when the information will arrive.
WHAT I'VE DONE SO FAR:
My HTTP request and parsing JSON class:
WeatherAPI::WeatherAPI(QObject *parent) : QObject(parent) {
manager = new QNetworkAccessManager(this);
QObject::connect(manager, SIGNAL(finished(QNetworkReply * )), this, SLOT(readData(QNetworkReply * )));
}
void WeatherAPI::readData(QNetworkReply *reply) {
if (reply->error() == QNetworkReply::NoError) {
QString strReply = (QString) reply->readAll();
QJsonDocument jsonResponse = QJsonDocument::fromJson(strReply.toUtf8());
QJsonObject jsonObject = jsonResponse.object();
weatherObject.city = jsonObject["name"].toString();
weatherObject.temperature = QString::number(jsonObject["main"].toObject()["temp"].toDouble() - 273.15);
int ts = jsonObject["dt"].toInt();
weatherObject.time = QDateTime::fromSecsSinceEpoch(ts).toString("hh:mm");
auto weatherData = jsonObject["weather"].toArray()[0].toObject()["main"].toString();
if (weatherData == "Clouds") {
weatherObject.icon = "Sun.png";
}
} else {
qDebug() << "ERROR";
}
}
void WeatherAPI::requestDataForCity(const QString &city) {
QString link = linkTemplate.arg(city, key);
QUrl url(link);
manager->get(QNetworkRequest(url));
}
const WeatherObject &WeatherAPI::getWeatherObject() const {
return weatherObject;
}
Now here is my custom Widget:
void WeatherButton::initStyle(const QJsonValue &json) {
PolygonButtonWidget::initStyle(json);
auto cities = json.toObject()["cities"].toArray();
api = new WeatherAPI(this);
for (auto c: cities) {
QString city = c.toString();
api->requestDataForCity(city); // HERE I'm making the http request
WeatherObject data = api->getWeatherObject();//HERE I'm getting the DATA
m_title = data.city;
m_time = data.time;
m_icon = data.icon;
m_temperature = data.temperature;
}
}
In that function from WeatherButton::initStyle I'm going to make an HTTP request and also I'm going to place the data into the necessary variable. Now my question is... How can I wait for that data to be received and just after that to place them into those variables?
So far the only solution I know so far is to use a QEventLoop, but at that moment I'm going to basically convert an async call into a sync one, which is not quite what I want. I want to be fully async.
WeatherObject data = api->getWeatherObject(); //HERE I'm getting the DATA
No, you do not get the data here. WeatherAPI::readData is where you get the data.
That is the point of the Signal - Slot mechanism. You do not wait for an event to happen, but react to it via callback, i.e. slot.
Having that in mind, you have to rethink and extend your code. Here is one way to do this:
In the WeatherAPI class define a dataReady(const WeatherObject &weatherObject) signal
Emit this signal in WeatherAPI::readData like this:
void WeatherAPI::readData(QNetworkReply *reply) {
if (reply->error() == QNetworkReply::NoError) {
// the processing of the http response remains unchanged
// ...
emit dataReady(weatherObject);
} else {
qDebug() << "ERROR";
}
}
In the WeatherButton class define a onDataReady slot with the following implementation:
void WeatherButton::onDataReady(const WeatherObject &weatherObject) {
m_title = weatherObject.city;
m_time = weatherObject.time;
m_icon = weatherObject.icon;
m_temperature = weatherObject.temperature;
}
Connect the newly created signal and slot in WeatherButton::initStyle like this:
void WeatherButton::initStyle(const QJsonValue &json) {
PolygonButtonWidget::initStyle(json);
auto cities = json.toObject()["cities"].toArray();
api = new WeatherAPI(this);
connect(api, &WeatherAPI::dataReady, this, &WeatherButton::onDataReady);
for (auto c: cities) {
QString city = c.toString();
api->requestDataForCity(city); // HERE I'm making the http request
}
}
As a sidenote I should say, that initStyle is probably not the best place to instantiate the WeatherAPI. api seems to be an attribute of WeatherButton, hence it should be initialized in the constructor of the class.
My program is getting data from mysql table via json format through php script, that generating json.
My function sends to server post request (with some params) and getting response. With that all okay. Works fine.
But, when I want to get specified cell (data from json array), it takes empty string (program works fast and taking data from a string before it sets up)
Here's the code with post request:
void dbase::requestor(QString option)
{
curr_js = ""; //nulling string
QString urla = host+"transfer.php";
// /////////
QNetworkAccessManager * manager = new QNetworkAccessManager(this);
QUrl url(urla);
QNetworkRequest request(url);
request.setHeader(QNetworkRequest::ContentTypeHeader, "application/x-www-form-urlencoded");
QUrlQuery params;
params.addQueryItem("api", key);
params.addQueryItem("option", option);
//QEventLoop loop;
connect(manager, SIGNAL(finished(QNetworkReply *)),this, SLOT(replyFinished(QNetworkReply *)));
//loop.exec(); tryed eventloop, but bcuz of this my replyFinished is not accessible. error code under this one
manager->post(request, params.query().toUtf8());
}
If using eventloop
QObject::connect: No such slot QEventLoop::replyFinished(QNetworkReply *)
replyFinished function (setting up variable)
void dbase::replyFinished(QNetworkReply *reply)
{
curr_js = reply->readAll();
}
Usage (where is problem)
QString req = "SOME REQUEST";
database.requestor(req);
if (database.db_cell (0,0) == "")
{
qDebug()<<database.db_cell (0,0) << " - EMPTY - "<<database.curr_js;
}
So in this case I'm getting
"" - EMPTY - ""
But if I getting data from string (created button for test), it's there:
{"0":["1", "Admin","hashpwd"],"1":["2", "Albert","hashpwd"]}
db_cell function
QString dbase::db_cell (int indexrow, int indexcols)
{
QJsonDocument sd = QJsonDocument::fromJson(curr_js.toUtf8());
QJsonObject setobj = sd.object();
QJsonValue qqq = setobj.value(QString(QString::number(indexrow))).toArray()[indexcols];
return qqq.toString();
}
As I see, problem is that program need to wait before getting a data from json-string.
I would like to know, how to parse associative JSON arrays in QT.
This is my example JSON:
{
"req_code": 5,
"params": {
"email":"user#domain.com",
"password":"123"
}
}
So, in order to get email (from JSON string called 'data') I would have to do something like this:
QJsonDocument doc=QJsonDocument::fromJson(data.toUtf8());
QJsonObject jobj=doc.object();
QJsonValue params_value=jobj.value(QString("params"));
QJsonArray params_array=params_value.toArray();
Now, 'email' is being held in 'params_array' object, but this array is not a QHash and not a QMap. If it would be a QHash I would get email by:
QString email=params_array.value("email");
But it is not a hash, it is a vector. So how do I get the value of 'email' property in this case in a proper and fast way?
The value of params is an object, and QJsonObject provides map-like functions so you can easily access it:
auto doc = QJsonDocument::fromJson(data.toUtf8());
auto docObj = doc.object();
auto paramsObj = docObj["params"].toObject();
auto email = paramsObj["email"];
And documentation says:
All JSON classes are value based, implicitly shared classes.
so you don't really need to take much care of performance. If you want to conver QJsonObject to hash or map, you can use QJsonObject::toVariantHash or QJsonObject::toVariantMap.
Try this;
QJsonArray params_array = jobj.value("params").toArray();
qDebug() << "params_array:: results array size = " << params_array.count();
foreach (const QJsonValue & value, a)
{
QJsonObject obj = value.toObject();
qDebug() << "obj keys " << obj.keys() ;
// here you can access your data, verify your keys with the debug a
}
Alright, I found something I just don't understand. I am making a request to a web service using QtNetworkManager. For some reason I can't seem to go from the network response to a jsondoc directly, I have to cast it into a string and then BACK into uft8?
void WebAPIengine::handleNetworkData(QNetworkReply *networkReply)
{
//No network error
if (!networkReply->error()){
//Cast to string
QString strReply = (QString)networkReply->readAll();
//This works, jsonDoc will have the json response from webpage
QJsonDocument jsonDoc = QJsonDocument::fromJson(strReply.toUtf8());
//This doesn't work, networkReply->readAll() is said to return a QByteArray.
QJsonDocument jsonDoc2 = QJsonDocument::fromBinaryData(networkReply->readAll());
QJsonObject jsonObj = jsonDoc.object();
data = jsonObj;
}
//Network error
else{
data["Error"] = "WebAPIengine::handleNetworkData()";
}
Now I can not understand why jsonDoc is working and jsonDoc2 is not. Can someone explain?
Once you do a QNetworkReply->readAll(), the QNetworkReply object will be empty. So if you call the QNetworkReply->readAll() method again, you will not get anything.
Moreover I don't understand why you are converting the QByteArray returned by QNetworkReply->readAll() into a QString and then converting it back to QByteArray(by calling QString::toUtf8()) to give it to the QJsonDocument::fromJson function.
You can try doing this:
QByteArray temp = newReply->readAll();
QJsonDocument jsonDoc = QJsonDocument::fromJson(temp); // This should work
Also make sure to know what the content of the JSon document is, i.e. if it is a map (QJsonObject), array(QJSonArray), array of maps or map with an array as value.
Apologies for asking something this trivial but I just can't seem to get it right so I guess I've completely misunderstood everything I thought I knew about memory management.
I have a function that parses a network reply for some data and it looks like this:
// Call from another function
QVariantMap *mappedResult = handleReply(reply);
...
// Function
QVariantMap *handleReply(QNetworkReply *reply) {
QVariantMap *result = new QVariantMap;
QVariant testvalue = new QVariant("testvalue");
result->insert("testkey", testvalue);
if (reply->error() > 0) {
qDebug() << "Error number = " + reply->errorString();
QVariant variant = QVariant.fromValue(reply->errorString());
result->insert("error", variant);
} else {
QJsonDocument jsonResponse = QJsonDocument::fromJson(jsonString.toUtf8());
QJsonObject jsonResponseObject = jsonResponse.object();
*result = jsonResponseObject.toVariantMap();
}
return result;
}
If there is no error, the result is parsed fine by the built in toVariantMap function. When there is an error however, I would like to create an entry in the result that is sent back from the function. As you can see in the function, I'm trying to create QVariants from Strings in two different ways.
The first approach gives an error like this:
C:\Qt\5.2.0\mingw48_32\include\QtCore\qvariant.h:466: error: 'QVariant::QVariant(void*)' is private inline QVariant(void *) Q_DECL_EQ_DELETE;
^
The second approach like this:
[PATH] error: expected primary-expression before '.' token QVariant variant = QVariant.fromValue(reply->errorString());
I've also tried setting the values like this:
result->insert("testkey", "testvalue");
result->insert("error", reply->errorString());
The last approach doesn't give compile errors but the result variable in the return statement cannot be inspected in the debugger and as soon as the return statement is executed the application crashes with memory problems indicating I'm not using "new" properly.
"Error accessing memory address 0x...".
If someone with at least a little knowledge could help me sort out how to perform this simple task, I would be very greatful. How can I return a QVariantMap from my function with custom strings as key/value pairs?
Cheers.
I would write your function in the following way (with fixes):
QVariantMap *handleReply(QNetworkReply *reply) {
QVariantMap *result = new QVariantMap;
QVariant testvalue("testvalue"); // <- fixed here
result->insert("testkey", testvalue);
if (reply->error() > 0) {
qDebug() << "Error number = " + reply->errorString();
QVariant variant(reply->errorString()); // <- fixed here
result->insert("error", variant);
} else {
QJsonDocument jsonResponse = QJsonDocument::fromJson(jsonString.toUtf8());
QJsonObject jsonResponseObject = jsonResponse.object();
*result = jsonResponseObject.toVariantMap();
}
return result;
}
However it is still unclear, why do you need to work with a pointer to the variant map instread of passing it by value?