General and Desktop

• 

  How to create the plugin of MYSQL for Qt
  • BlackStar

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  @flydragon

  Do not duplicate posting because you do not get an answer immendiately.

  [edit:koahnig see https://forum.qt.io/topic/82629/why-qsqlquery-exec-exit-failed ]

• 

  Reporting inappropriate content on the forums
  spam • • Eddy

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  Thank you for the report. I have banned the user, which got rid of the spam posting. Not a loss, as this user did not post any other content on the site. Just deleting this one posting was not possible.

  Thanks for reporting this.

• 

  Unsolved Timer Cannot Stop..?
  • PrAnit

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  Hi
  timer is a single shot so should not be running.
  and you should call
  timer2->Stop();

  in STOP button.

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  Unsolved Segmentation Fault when reading from a TCPSocket
  • onurcevik

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  Hi,

  One small note, use qobject_cast when casting QObject based classes. This will return a null pointer if either the source is already a null pointer or not from the correct class.

• 

  Unsolved migrate old application
  • aminemaar

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  Hi
  Can you explain a bit more about

  So there is any methode to include the external application.
  as the app would still be a windows only app and would not run on other platforms.

  So what part of the app is tied to windows?
  html5, css, js, kendoUI, seems cross platform by nature but
  depends on what app is.

• 

  Unsolved What calls paintGL
  • BKBK

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  Calling update() does refresh the screen. When the app stopped all displays within the QGLWidget I messed around for several days trying to find the problem, then finally called a function to display static data. At first it did not work, then I explicitly called update() and it worked. Then I restored some code that had written to see how often paintGL() was being called. That showed that it was not being called.
  It was being called at 60Hz. I don't know what I did not stop those calls.
  This is a Qt app with a single QGLWidget that is used to display a strip chart.

• 

  Unsolved QFileDialog::getOpenFileName
  • meikelneit

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  @meikelneit
  Hi
  with QFileDialog::getOpenFileName static call, if user press Cancel or close X the
  returned string will be empty.

  QString l_filePath = QFileDialog::getOpenFileName(this,tr("open directory"),QDir::homePath(),("*.db")); if ( ! l_filePath.isEmpty() ) { // if user did select something .... }
• 

  Unsolved How to have the most updated QT libraries?
  • lucaszanella

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  @jsulm said in How to have the most updated QT libraries?:

  DCMAKE_PREFIX_PATH

  I did make VERBOSE=1 to see which paths were being used and the path I passed isn't

• 

  Unsolved Failure to return file paths in server 2008 qt QDirIterator
  • ErfanCoder

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  @mrjj said in Failure to return file paths in server 2008 qt QDirIterator:

  Hi and welcome to the forums.
  Are you certain you have rights to enumerate folder in c:\ for the user account on the server ?

  yes ,
  im using qt 5.8 msvc2015

• 

  Unsolved QJSEngine, how to expose C++ enum to a JavaScript?
  • Alhasni

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  Hi @Alhasni,

  According to https://doc.qt.io/qt-5/qjsengine.html#qobject-integration I guess you need to use QJSEngine::newQMetaObject():

  QJSValue enumObjectValue = _jsEngine.newQMetaObject(_controller->metaObject()); _jsEngine.globalObject().setProperty("controller", enumObjectValue);
• 

  Unsolved QSortFilterProxyModel not mapping properly
  qsorfilterproxy qmodelindex itemmodel • • zmurphy

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  Yes, here's the top level class. There's a handful of subclasses but I don't believe they do interactions with the Model/View aspects.

  class CxFVariableItemModel : public QAbstractItemModel { public: CxFVariableItemModel () : QAbstractItemModel () { } virtual ~CxFVariableItemModel () {} const QList <QString> &headers () const { return _headers; } virtual const QList <QString> &possibleHeaders () const = 0; void setHeaders (const QList <QString> &headers) { emit layoutAboutToBeChanged (); _headers = headers; emit layoutChanged (); } virtual const bool useLabels (int whichSensor) = 0; virtual const QList <LabelReturnType> &getUsefulStrings (bool returnLabels, int whichSensor) = 0; virtual const char *getVariableName (int whichSensor) = 0; virtual const int getWhichRow (const char *name) = 0; virtual const int depVarSize (int whichSensor, int i) = 0; virtual const char *getRealDependName (const int whichSensor, const int whichDependSensor) = 0; /// Will return a list of all possible timing variable names virtual const QList <QString> getListOfTimingVariableNames () = 0; /// Will return a list of all possible variable names virtual const QList <QString> getListOfVariableNames () = 0; QModelIndex index (int row, int column, const QModelIndex &parent = QModelIndex ()) const { if (!hasIndex (row, column, parent)) { return QModelIndex (); } if (parent == QModelIndex ()) { return createIndex(row, column); } if (_headers [column] == "Other") { return createIndex (row, column, reinterpret_cast <void *> (parent.row () + 1)); } return QModelIndex (); } QModelIndex parent (const QModelIndex &index) const { // We used to have index.parent ().row () but that causes an issue when we only had one variable in the GUI. long parentRow = index.row (); if (parentRow == 0) return QModelIndex (); else { return createIndex (parentRow - 1, 0); } } virtual int rowCount (const QModelIndex &parent) const = 0; int columnCount (const QModelIndex &) const { return _headers.size (); } virtual QVariant data (const QModelIndex &index, int role = Qt::DisplayRole) const = 0; QVariant headerData (int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const { if (role == Qt::DisplayRole) { if (orientation == Qt::Horizontal) { return QVariant (_headers [section]); } else { // vertical return (QVariant (section)); } } return (QVariant ()); } protected : QList <QString> _headers; };

  Some of this code is quite old so it may not necessarily be correct according to current Qt Model/View standards which is where I think the problem lies.

• 

  Unsolved Need to use QCryptographicHash and convert an STL function
  • vivian

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  @jsulm Thank you for that.. I just did a straight up copy.

  Now just stuck at the last part where the SHA1 and then converting to base64

  string utf8String = wstring_to_utf8(keyaccessGuid); unsigned char digestStr2[SHA_DIGEST_LENGTH]; SHA1((unsigned char*)utf8String.c_str(), strlen(utf8String.c_str()), (unsigned char*)&digestStr2); char* utf8StrSha1Base64 = convertToBase64(digestStr2, SHA_DIGEST_LENGTH); string sha1DataStr(utf8StrSha1Base64); //Remove all characters except alphabets removeForbiddenChar(&sha1DataStr);

  This is what I am trying to do.

  { ... QString utf8String = keyaccessGuid.toUtf8(); QByteArray resBytes(utf8String.toStdString().c_str()); QCryptographicHash sha(QCryptographicHash::Sha1); sha.addData(resBytes); QByteArray shaBytes = sha.result(); qDebug()<<"Resulting Hash is "; QString resHash = base64_encode(shaBytes); qDebug()<<resHash ; } QString base64_encode(QByteArray ba){ return ba.toBase64(); } QByteArray base64_decode(QByteArray ba){ return QByteArray::fromBase64(ba); }

  I am hoping I am on the right track.

• 

  Unsolved C++ signal QML slot with QObject as parameter but sometimes QML receives null
  • Prasad_Socionext

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  Unsolved Main Project do not update after Static Library Change
  • mahd96

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  Unsolved QJSEngine, how to import other scripts?
  • Alhasni

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  According to this question, it doesn't appear that this is supported.

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  Unsolved Is there have relationship between QWidget and QWindow after QWindow pop up?
  • richie18

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  The environment:
  Python 3.6.8
  PyQt 5.7.1
  pywin32-224-cp36-cp36m-win_amd64

• 

  Unsolved Can I host QT based apps on DigitalOcean cloud servers.?
  • MariaWilliams

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• 

  Unsolved How to align a table created using HTML to center
  • ManiRon

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  @ManiRon
  To align table centrally horizontally, use one of the following:

  <table style="margin-left: auto; margin-right: auto;"> <table style="margin-left: 0; margin-right: auto;"> Put table inside <div></div> and align that.

  The above may assume you have something like html, body { width: 100%; } so that it knows what to center within, I'm not sure, you might have to play.

• 

  Solved program crashes after assigning values to array elements
  • rezaMSLM

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  @J.Hilk said in program crashes after assigning values to array elements:

  Try deleting your build folder for a clean rebuild,

  I think this solved my problem
  no crash has occurred since I did that.
  Thankyou J.hilk and jsulm for your help

  but I don't understand why rebuilding was the solution

• 

  Unsolved upgrade SDK on macOs Qt version
  • AmirAbbasi

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  @AmirAbbasi
  also I updated my macOS to high sierra 10.13.6 (17G65)

• 

  Unsolved QGraphicsScene Delete Item Error
  • Pada_

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  Question is not very clear. Can you show us the images or screen with your behaviour. What is the exact issue ?

• 

  Solved LNK 2019 Error
  • meikelneit

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  No i said that i little bit unclear, i just meant as information for you the constructor was missing. But it is solved now. I had to delete the QT and c++ build folder, then i just cleaned, run Remake and rebuild, then it worked. My experience now says, that LNK error is not a syntax problem in 99% of all cases .

  "solved"

• 

  Unsolved Running Qt Application from .dll
  • Theok

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  Thanks for reply,
  if i understand correct you need to define which classes,functions will be exported from the library so the user can use-call to his main app.

  #if defined(MYLIBRARY_LIBRARY) # define MYLIBRARYSHARED_EXPORT Q_DECL_EXPORT #else # define MYLIBRARYSHARED_EXPORT Q_DECL_IMPORT #endif

  This is the code of the xxx_myglobal.h header file that is automatically created when i create a C++ library project (The names changed with your recommendation so instead of MYLIBRARYSHARED_EXPORT before was DLLSHARED_EXPORT ). The .pro file of the shared library project is :

  #------------------------------------------------- # # Project created by QtCreator 2019-02-19T10:28:30 # #------------------------------------------------- QT += widgets TARGET = MyLibrary TEMPLATE = lib DEFINES += MYLIBRARY_LIBRARY # The following define makes your compiler emit warnings if you use # any feature of Qt which has been marked as deprecated (the exact warnings # depend on your compiler). Please consult the documentation of the # deprecated API in order to know how to port your code away from it. DEFINES += QT_DEPRECATED_WARNINGS # You can also make your code fail to compile if you use deprecated APIs. # In order to do so, uncomment the following line. # You can also select to disable deprecated APIs only up to a certain version of Qt. #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0 SOURCES += \ mylibrary.cpp HEADERS += \ mylibrary.h \ mylibrary_global.h \ ui_windowlibrary.h unix { target.path = /usr/lib INSTALLS += target }

  Do you think the problem is on the C++ library project? This project builds fine but when i try to call the library from another application then comes the errors i wrote in the top...

• 

  Solved QProgressDialog not displayed
  • robcont_

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  @mrjj said in QProgressDialog not displayed:

  Hi
  Best guess is that the variable
  QProgressDialog progress;
  is deleted very soon as the function ends.
  so even thread lives, the actual QProgressDialog does not.

  try
  QProgressDialog *progress = new QProgressDialog("Installing...", "Abort", 0, 0, this);

  Thanks it works! It was a very simple solution.

• 

  Unsolved Layout not respecting sizes
  • GrahamLa

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  Strange...
  Can you try this minimal example?

  #include <QApplication> #include <QSlider> #include <QLabel> #include <QHBoxLayout> int main(int argc, char ** argv) { QApplication app(argc,argv); QWidget mainWid; mainWid.setMinimumSize(600,10); QLabel *label1 = new QLabel("Test1",&mainWid); QLabel *label2 = new QLabel("Test2",&mainWid); QSlider* slider = new QSlider(Qt::Horizontal,&mainWid); slider->setRange(0,100); slider->setSizePolicy(QSizePolicy::Preferred,QSizePolicy::Preferred); QHBoxLayout* mainLay = new QHBoxLayout(&mainWid); mainLay->addWidget(label1); mainLay->addItem(new QSpacerItem(1,1,QSizePolicy::Expanding,QSizePolicy::Preferred)); mainLay->addWidget(label2); mainLay->addWidget(slider); mainWid.show(); return app.exec(); }
• 

  Unsolved QSharedPointer in destructed signal parameter deletes object which has other QSharedPointer
  • fatih.erol

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  Thank you. I should have read QEnableSharedFromThis documentation.

  You can inherit this class when you need to create a QSharedPointer from any instance of a class; for instance, from within the object itself. The key point is that the technique of just returning QSharedPointer<T>(this) can not be used, because this winds up creating multiple distinct QSharedPointer objects with separate reference counts. For this reason you must never create more than one QSharedPointer from the same raw pointer.

  I guess, the pointer was being smart, but I was not, by initiating one from 'this' pointer in signal. That does not really convey ownership semantics particularly. I must have assumed the references were counted globally based on shared pointer objects pointing to the raw pointer value. Event member could be a raw pointer instead.

  The example was carved roughly to test the issue. No particular reason QCoreApplication was a pointer; I pulled it out of main to handle 'Ctrl+C', although the method might go against "You can't call Qt functions from Unix signal handlers." Also, I wanted to explicitly delete Manager on 'Ctrl+C'.

  QSharedPointer documentation does not have any warning about pointing to QObject-derived classes. Actually, it does so in examples setting custom deleter to Object::deleteLater. I guess, it can conflict with Qt's parent/child mechanism.

• 

  [SOLVED] - QTableView - change cursor when hovering specific column
  • maximus

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  Hi, I used the above code in my customTableView and Its changing the mouse cursor but from second time(Not for the first time).
  And when its changed to Hand cursor, Its not going back to Arrow cursor for another column.
  Looks like the move event is not calculating the pos() every time on mouse move.
  I have already installed the event filter and setMouseTracking as true.
  Is there anything I am missing?

• 

  Unsolved What is the difference between macros Q_INVOKABLE and Q_PROPERTY?
  • Ronak5

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  @Ronak5 said in What is the difference between macros Q_INVOKABLE and Q_PROPERTY?:

  I'm bit confused regarding on what basis and how do I decide which macro to be used and when?

  Q_PROPERTY is a property (with a getter, maybe a setter, notifier signal, etc) which enables you bindings etc.

  Q_INVOKABLE simply marks a method to be callable via moc (and thus also via QML for example), nothing more. Similar to slots for example.

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  Unsolved update qsqlite and qtableview
  • Mogli123

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• 

  Unsolved Half Duplex mode in Qt
  • EvanZ

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  AFAIK, the serial port device always work in full-duplex. A half/full duplex makes not sense for RS232/TTL interfaces. It makes sense only for RS485/422 interfaces.

  As I understand, RFID just echoing each command. Maybe it is possible to disable this default RFID behavior by sending some commands to RFID (see datasheet on yor RFID).

  About the RealTerm and its "Half-Duplex" mode: I don't see any specific options to control the serial port handle there (in those Deplhi sources) to enable the "Half-Duplex" mode. I assume, that this mode are implemented in the programmatically way (it just ignores the received echo).

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  Unsolved TaskBar-Icon hidden when MainWindow hidden
  • Toby

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  No one has replied

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  Unsolved how to build QtSingleApplication for qt version 5.11.2
  • Bharth

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  @Bharth Did you read https://github.com/qtproject/qt-solutions/blob/master/qtsingleapplication/INSTALL.TXT ?

• 

  Solved How to create a pop up message like message box with a countdown?
  messagebox countdown • • Z0mbi3

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  @Z0mbi3 said in How to create a pop up message like message box with a countdown?:

  QObject::connect(&cntDown, &QTimer::timeout, &msg,&cnt, &cntDown->void{…

  Hi,

  there's a lot to unpack in that simple question :)

  But it's part of the essential functionality of Qt, know as the Signal&Slot mechanisms.
  For further read on the topic take a look at the documentation:
  https://doc.qt.io/qt-5/signalsandslots.html

  Let me boil it down for you.
  The QTimer-Object is emitting a signal(void timeout()) each time the set interval has passed. (1000 ms in the above example)

  with the connect function of the QObject class we listen to the timeout signal and decide what shall happen when the signal is emitted.

  In the above case, the signal is connected to a lambda function - more informations on lambdas can be found here: https://de.cppreference.com/w/cpp/language/lambda

  The objects msg, int and cntDown are captured for the lambda, so that they can be used inside of it,

  Inside the () would go any arguments that timeout has and would be used inside the lambda. It's empty because void timeout() has no arguments.

  ->void defines the return type of the lambda

  inside {} is the actual function

• 

  This topic is deleted!
  • Pada_

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  Unsolved Connect a checkbox widget to a line edit to appear when toggled box
  • AXNT

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  @AXNT

  Can you clean and rebuild solution ?
  When you type ui-> does be any suggestion for advsearch Checkbox?
  can you check if advsearch is missspelled?
  also can you show contents of mainwindow.ui?

• 

  Unsolved Problem with MySQL driver on mac
  • Albert Huert

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  @kenchan Thank you very much for the help.

• 

  Unsolved Accessing the Plugin metadata starting from a QObject*
  • Lolo67

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  @StefanBruens said in Accessing the Plugin metadata starting from a QObject*:

  Unless the metaData is passed back from the loader to the plugin instance, it seems to be unavailable.

  The meta data is not available through the QObject, get it from the loader if you need it. Strictly speaking Q_PLUGIN_METADATA is a moc artifact that facilitates the plugin loading and you shouldn't really need it to begin with, while on the other hand the QObject you get isn't a plugin it's the entry point for the plugin.

• 

  Unsolved My custom QML item always have the size of the window
  qml c++ • • lucaszanella

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• 

  Unsolved "nullptr" was not declared in scope
  • Nafab213

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  Hi,

  To add to my fellows: the suggestion is to update to 5.12 not 5.1.2.

• 

  Solved SSL problem on linux/windows
  ssl segfault openssl linux • • borghe

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  Hi,

  Not the same backend used. Unless you re-build Qt and force the use of OpenSSL. Qt on macOS uses Apple's SecureTransport framework. OpenSSL on that platform has been deprecated a long time ago.