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Save QSet using QSettings

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  • M Offline
    M Offline
    mpergand
    wrote on last edited by
    #4

    I've got this error with QSettings:

    QVariant::save: unable to save type 'QSet<QString>' (type id: 1092).
    QVariant::load: unable to load type 1092.
    

    I have no clue unfortunately ...

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    • U Offline
      U Offline
      user4592357
      wrote on last edited by
      #5

      i guess i'll just use QStringList...

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      • U Offline
        U Offline
        user4592357
        wrote on last edited by
        #6

        well, and another question i have, is...

        i read the settings file from the "main" class where i have all my widgets. however, every widget has some specific properties that other widgets don't. and i want to read that property from the settings file. is it considered a good practice to read the same settings file from a few places?

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        • M Offline
          M Offline
          mpergand
          wrote on last edited by mpergand
          #7

          Yes, it is what QSettings is made for.
          From Qt doc:

          If you use QSettings from many places in your application, 
          you might want to specify the organization name and the application name using 
          QCoreApplication::setOrganizationName() and QCoreApplication::setApplicationName(), 
          and then use the default QSettings constructor:
          
                QCoreApplication::setOrganizationName("MySoft");
                QCoreApplication::setOrganizationDomain("mysoft.com");
                QCoreApplication::setApplicationName("Star Runner");
                ...
                QSettings settings;
          
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          • SGaistS Offline
            SGaistS Offline
            SGaist
            Lifetime Qt Champion
            wrote on last edited by
            #8

            @mpergand said in Save QSet using QSettings:

            QVariant::load: unable to load type 1092

            You have to implement the corresponding stream operators see qRegisterMetaTypeStreamOperators

            Interested in AI ? www.idiap.ch
            Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

            U 1 Reply Last reply
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            • M Offline
              M Offline
              mpergand
              wrote on last edited by
              #9

              @SGaist
              Yes, I supposed something like that.
              That's strange, you can serialize a QSet as is with QDataStream, but not with QVariant !

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              • SGaistS SGaist

                @mpergand said in Save QSet using QSettings:

                QVariant::load: unable to load type 1092

                You have to implement the corresponding stream operators see qRegisterMetaTypeStreamOperators

                U Offline
                U Offline
                user4592357
                wrote on last edited by user4592357
                #10

                @SGaist

                thanks, that's what i needed.

                this is how i did it. i set breakpoints to on operator << and >> to see how they work, but i can't spot the mistake. when i read the settings, i.e writeSettings() function, i get one more invalid entry read from in-stream. of course i can check its validity but i wanna understand where it comes from:

                void HighScores::readSettings() {
                	QSettings settings { m_sSettingsFile, QSettings::IniFormat };
                
                	const auto highScores = settings.value("highScores");
                
                	if(highScores.isValid())
                		m_highScores = highScores.value<QVariantMultiMap_t>();
                	else
                		m_highScores = QVariantMultiMap_t {};
                }
                
                void HighScores::writeSettings() const {
                	QSettings settings { m_sSettingsFile, QSettings::IniFormat };
                
                	settings.setValue("highScores", qVariantFromValue(m_highScores));
                }
                
                QDataStream &operator<<(QDataStream &out, const HighScores::QVariantMultiMap_t &mmap) {
                	const auto mmapEnd = mmap.constEnd();
                	for(auto it = mmap.constBegin(); it != mmapEnd; ++it)
                		out << it.key() << it.value();
                	return out;
                }
                
                QDataStream &operator>>(QDataStream& in, HighScores::QVariantMultiMap_t& mmap) {
                	QVariant key;
                	QString value;
                	while(!in.atEnd()) {
                		in >> key >> value;
                		mmap.insert(key, value);
                	}
                	return in;
                }
                

                where

                using QVariantMultiMap_t = QMultiMap<QVariant, QString>;
                QMultiMap<QVariant, QString> m_highScores;
                

                i've put Q_DECLARE_METATYPE(HighScoresPage::QVariantMultiMap_t) in header file after class declaration, and qRegisterMetaTypeStreamOperators<QVariantMultiMap_t>("QVariantMultiMap_t"); in constructor

                which part am i doing wrong?

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                • M Offline
                  M Offline
                  mpergand
                  wrote on last edited by mpergand
                  #11

                  I found a similar topic with a clear anwser :
                  [https://forum.qt.io/topic/78161/custom-class-serialize-with-qdatastream](link url)

                  I made a test with a QSet<QString>

                  typedef QSet<QString>  QStringSet;
                  Q_DECLARE_METATYPE(QStringSet)
                  
                  int main(int argc, char *argv[])
                  {
                      qRegisterMetaTypeStreamOperators<QStringSet>("QStringSet");
                      QString home=QDir::homePath();
                      QString iniFileName="config.ini";
                      QString iniPath=home+"/"+iniFileName;
                      QSettings settings(iniPath,QSettings::IniFormat);
                  
                      QStringSet setIn;
                      QVariant varIn;
                      setIn<<"A"<<"B"<<"C";
                  
                      // save
                      varIn.setValue(setIn);
                      settings.setValue("Set",varIn);
                  
                      // load
                      QVariant varOut=settings.value("Set");
                      QStringSet setOut=varOut.value<QStringSet>();
                  
                  qDebug()<<"in "<<setIn;
                  qDebug()<<"out"<<setOut;
                  
                  return 0;
                  }
                  

                  For QSet, no << operator needed, just to declare the type.
                  All seems to work and the ini file looks good.

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                  • U Offline
                    U Offline
                    user4592357
                    wrote on last edited by user4592357
                    #12

                    my code actually works, but not correctly

                    the part that goes wrong in my code is in while loop in QDataStream &operator>>(QDataStream& in, HighScores::QVariantMultiMap_t& mmap). i check the stream using

                    while(!in.atEnd()) {
                        // read from stream 
                    }
                    

                    when i have, say, 1 element in the container, the saving of it in stream is done correctly. however, when reading from the stream, the execution enter the loop one time, and then one more extra time and i get an invalid element saved in container

                    p.s.
                    i tried with QStringSet but with this things are worse, writing to settings is okay, but reading always returns QVariant::Invalid:

                    void UsernamePage::readSettings() {
                    
                    	QSettings settings { filePath, QSettings::IniFormat };
                    	const auto usernames = settings.value("usernames"); // <-- returns Invalid
                    	if(usernames.isValid())
                    		m_usernames = usernames.value<QStringSet_t>();
                    	else
                    		m_usernames = QStringSet_t {};
                    }
                    
                    void UsernamePage::writeSettings() const {
                    
                    	QSettings settings { filePath, QSettings::IniFormat };
                    	settings.setValue("usernames", qVariantFromValue(m_usernames));
                    }
                    
                    QDataStream &operator<<(QDataStream &out, const ChooseUsernamePage::QStringSet_t &sset) {
                    	const auto ssetEnd = sset.constEnd();
                    	for(auto it = sset.constBegin(); it != ssetEnd; ++it)
                    		out << *it;
                    	return out;
                    }
                    
                    QDataStream &operator>>(QDataStream &in, ChooseUsernamePage::QStringSet_t &sset) {
                    	QString username;
                    	while(!in.atEnd()) {
                    		in >> username;
                    		sset.insert(username);
                    	}
                    	return in;
                    }
                    
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                    • M Offline
                      M Offline
                      mpergand
                      wrote on last edited by mpergand
                      #13

                      If you are using QSet or QMap, you don't need to implement the << operator cause it's alreday the case. You only need to declare the type.

                      Example with a QMap:

                      typedef QMap<QString,QVariant>  Map;
                      qRegisterMetaTypeStreamOperators<Map>("Map");
                      
                          Map mapIn;
                          QVariant varIn;
                          mapIn["string"]="Hello";
                          mapIn["num"]=1000;
                          // save
                          varIn.setValue(mapIn);
                          settings.setValue("Map",mapIn);
                      
                          // load
                          varOut=settings.value("Map");
                          Map mapOut=varOut.value<Map>();
                      
                      qDebug()<<"in "<<mapIn;
                      qDebug()<<"out"<<mapOut;
                      

                      Logs:

                      in  QMap(("num", QVariant(int, 1000))("string", QVariant(QString, "Hello")))
                      out QMap(("num", QVariant(int, 1000))("string", QVariant(QString, "Hello")))
                      

                      You only need to implement the stream ops for your custom classes.

                      [edit] QMap is a wrong example because it's already managed by QVariant :)

                      It's only needed fot QSet !

                      U 1 Reply Last reply
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                      • M mpergand

                        If you are using QSet or QMap, you don't need to implement the << operator cause it's alreday the case. You only need to declare the type.

                        Example with a QMap:

                        typedef QMap<QString,QVariant>  Map;
                        qRegisterMetaTypeStreamOperators<Map>("Map");
                        
                            Map mapIn;
                            QVariant varIn;
                            mapIn["string"]="Hello";
                            mapIn["num"]=1000;
                            // save
                            varIn.setValue(mapIn);
                            settings.setValue("Map",mapIn);
                        
                            // load
                            varOut=settings.value("Map");
                            Map mapOut=varOut.value<Map>();
                        
                        qDebug()<<"in "<<mapIn;
                        qDebug()<<"out"<<mapOut;
                        

                        Logs:

                        in  QMap(("num", QVariant(int, 1000))("string", QVariant(QString, "Hello")))
                        out QMap(("num", QVariant(int, 1000))("string", QVariant(QString, "Hello")))
                        

                        You only need to implement the stream ops for your custom classes.

                        [edit] QMap is a wrong example because it's already managed by QVariant :)

                        It's only needed fot QSet !

                        U Offline
                        U Offline
                        user4592357
                        wrote on last edited by
                        #14

                        @mpergand i still get invalid qvariant :(

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                        • M Offline
                          M Offline
                          mpergand
                          wrote on last edited by mpergand
                          #15

                          My Example of HighScores implementation.
                          I'm using a custom class Gamer:

                          struct Gamer
                          {
                              QString name;
                              int highScore;
                          
                          };
                          
                          Q_DECLARE_METATYPE(Gamer)
                          
                          QDataStream &operator<<(QDataStream &out, const Gamer &gamer) {
                          
                              out<<gamer.name<<gamer.highScore;
                          
                              return out;
                          }
                          
                          QDataStream &operator>>(QDataStream &in, Gamer &gamer) {
                          
                              in>>gamer.name;
                              in>>gamer.highScore;
                          
                              return in;
                          }
                          // for qDebug logs
                          QDebug operator<<(QDebug debug, const Gamer &gamer)
                          {
                              debug<<gamer.name<<", "<<gamer.highScore;
                              return debug;
                          }
                          

                          Saving HighScores in a QList<Gamer>:

                          using  HighScores=QList<Gamer>;
                          qRegisterMetaTypeStreamOperators<HighScores>("HighScores");
                          
                          Gamer g1{"John", 1200};
                          Gamer g2{"Irvin", 2200};
                          Gamer g3{"Lisa", 2140};
                          
                          HighScores scores;
                          scores<<g1<<g2<<g3;
                          QVariant v; v.setValue(scores);
                          settings.setValue("HighScores",v);
                          
                          // load
                           v=settings.value("HighScores");
                          scores=v.value<HighScores>();
                          qDebug()<<scores;
                          

                          Output of scores:

                          ("John", 1200, "Irvin", 2200, "Lisa", 2140)
                          
                          U 1 Reply Last reply
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                          • M mpergand

                            My Example of HighScores implementation.
                            I'm using a custom class Gamer:

                            struct Gamer
                            {
                                QString name;
                                int highScore;
                            
                            };
                            
                            Q_DECLARE_METATYPE(Gamer)
                            
                            QDataStream &operator<<(QDataStream &out, const Gamer &gamer) {
                            
                                out<<gamer.name<<gamer.highScore;
                            
                                return out;
                            }
                            
                            QDataStream &operator>>(QDataStream &in, Gamer &gamer) {
                            
                                in>>gamer.name;
                                in>>gamer.highScore;
                            
                                return in;
                            }
                            // for qDebug logs
                            QDebug operator<<(QDebug debug, const Gamer &gamer)
                            {
                                debug<<gamer.name<<", "<<gamer.highScore;
                                return debug;
                            }
                            

                            Saving HighScores in a QList<Gamer>:

                            using  HighScores=QList<Gamer>;
                            qRegisterMetaTypeStreamOperators<HighScores>("HighScores");
                            
                            Gamer g1{"John", 1200};
                            Gamer g2{"Irvin", 2200};
                            Gamer g3{"Lisa", 2140};
                            
                            HighScores scores;
                            scores<<g1<<g2<<g3;
                            QVariant v; v.setValue(scores);
                            settings.setValue("HighScores",v);
                            
                            // load
                             v=settings.value("HighScores");
                            scores=v.value<HighScores>();
                            qDebug()<<scores;
                            

                            Output of scores:

                            ("John", 1200, "Irvin", 2200, "Lisa", 2140)
                            
                            U Offline
                            U Offline
                            user4592357
                            wrote on last edited by
                            #16

                            @mpergand that works but something's wrong with my code i guess?

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                            • U Offline
                              U Offline
                              user4592357
                              wrote on last edited by
                              #17

                              i have a deadline so for now i'll use QStringList instead of QSet<Qstring>. after it i'll (hopefully) try to find what was the problem

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