Add to Qt GUI logger functionality
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@JonB said in Add to Qt GUI logger functionality:
Not sure where to declare the log function though
At this point what I did is
I created a QApplication subclass in a .h file (integer_interface.h) which looks like this
class integer_interface : public QApplication { Q_OBJECT public: integer_interface(int &argc, char *argv[]) {}; // empty constructor signals: void libraryLogged(std::string message); };then in my logger_widget class, logger_widget.h (the one that contains the QPlainTextWidget) I have the following class definition:
namespace Ui { class logger_widget; } class logger_widget : public QWidget { Q_OBJECT public: explicit logger_widget(QWidget *parent = nullptr); ~logger_widget(); signals: public slots: void onLibraryLogged(std::string message); private: Ui::logger_widget *ui; integer::logger::errors err_init; integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance(); integer_interface *myApp = qobject_cast<integer_interface *>(qApp); };and a declaration of the log static function outside the class
static void log(std::string message);In the logger_widget constructor I have the following two lines to define the connection
integer::logger::g_loggerCallback = log; connect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);while log and onLibraryLogged implementations look like this
void logger_widget::onLibraryLogged(std::string message) { ui->plainTextEdit_logger->appendPlainText(QString::fromStdString(message)); } void log(std::string message) { integer_interface *myApp = qobject_cast<integer_interface *>(qApp); emit myApp->libraryLogged(message); }constructor and function implementations are obviously in the corresponding logger_widget.cpp file
It compiles fine, but I get a runtime error "abort()" and the following message
qt.core.qobject.connect: QObject::connect(integer_interface, logger_widget): invalid nullptr parameter@Gaetano03
So I assume that occurs at runtime when it hitsconnect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);and indicates one of the two objects are
nullptr. Check on line above with e.g.qDebug() << myApp << this;?
If
myApp == nullptr, you did remember to create aninteger_interface, not just aQApplicationnow, didn't you...??Everywhere you go
integer_interface *myApp = qobject_cast<integer_interface *>(qApp);you might follow that withQ_ASSERT(myApp);to verify all is well at that instant.P.S.
integer_interface(int &argc, char *argv[]) {}; // empty constructorDo you have
integer_interface(int &argc, char *argv[]) : QApplication(argc, argv)somewhere? -
@Gaetano03
So I assume that occurs at runtime when it hitsconnect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);and indicates one of the two objects are
nullptr. Check on line above with e.g.qDebug() << myApp << this;?
If
myApp == nullptr, you did remember to create aninteger_interface, not just aQApplicationnow, didn't you...??Everywhere you go
integer_interface *myApp = qobject_cast<integer_interface *>(qApp);you might follow that withQ_ASSERT(myApp);to verify all is well at that instant.P.S.
integer_interface(int &argc, char *argv[]) {}; // empty constructorDo you have
integer_interface(int &argc, char *argv[]) : QApplication(argc, argv)somewhere?@JonB
I think the problem might be where I define myApp is not correct? Which is at the moment into the logger_widget classwhen I qDebug as you said I get indeed the following value for myApp
QObject(0x0) logger_widget(0x1e04f63bcd0, name="logger_widget")and the app crashes few seconds after it starts
Should I declare the myApp out of any member class as I did for the log function?
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@Gaetano03
So I assume that occurs at runtime when it hitsconnect(myApp,&integer_interface::libraryLogged,this,&logger_widget::onLibraryLogged);and indicates one of the two objects are
nullptr. Check on line above with e.g.qDebug() << myApp << this;?
If
myApp == nullptr, you did remember to create aninteger_interface, not just aQApplicationnow, didn't you...??Everywhere you go
integer_interface *myApp = qobject_cast<integer_interface *>(qApp);you might follow that withQ_ASSERT(myApp);to verify all is well at that instant.P.S.
integer_interface(int &argc, char *argv[]) {}; // empty constructorDo you have
integer_interface(int &argc, char *argv[]) : QApplication(argc, argv)somewhere?@JonB said in Add to Qt GUI logger functionality:
If
myApp == nullptr, you did remember to create aninteger_interface, not just aQApplicationnow, didn't you...????
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@JonB said in Add to Qt GUI logger functionality:
If
myApp == nullptr, you did remember to create aninteger_interface, not just aQApplicationnow, didn't you...????
Do you have integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) somewhere?
ye I have it in an integer_interface.cpp, looks like this
#include "integer_interface.h" integer_interface::integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) { }??
I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?
Or maybe you meant something else from this
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Do you have integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) somewhere?
ye I have it in an integer_interface.cpp, looks like this
#include "integer_interface.h" integer_interface::integer_interface(int &argc, char *argv[]) : QApplication(argc, argv) { }??
I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?
Or maybe you meant something else from this
@Gaetano03 said in Add to Qt GUI logger functionality:
I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?
You should also instantiate it somewhere.
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@Gaetano03 said in Add to Qt GUI logger functionality:
I have it declared in my logger_widget.h class file (if you also see my previous reply), but was thinking maybe should be declared outside of the class?
You should also instantiate it somewhere.
I have it declared and instantiated both in the logger_widget.h class among the private members
private: Ui::logger_widget *ui; integer::logger::errors err_init; integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance(); integer_interface *myApp = qobject_cast<integer_interface *>(qApp);and in the static log function
void log(std::string message) { integer_interface *myApp = qobject_cast<integer_interface *>(qApp); emit myApp->libraryLogged(message); }as suggested by @JonB
PS
@JonB doing as you suggested as sanity check with the following linesinteger_interface *myApp = qobject_cast<integer_interface *>(qApp); Q_ASSERT(myApp);gives a bunch of errors not sure I understand:
logger_widget.h:42:14: C++ requires a type specifier for all declarationslogger_widget.h:42:5: Expected ')' 0:0: :42:5: note: to match this '(' logger_widget.h:42:14: Duplicate member 'myApp' logger_widget.h:41:24: previous declaration is here -
I have it declared and instantiated both in the logger_widget.h class among the private members
private: Ui::logger_widget *ui; integer::logger::errors err_init; integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance(); integer_interface *myApp = qobject_cast<integer_interface *>(qApp);and in the static log function
void log(std::string message) { integer_interface *myApp = qobject_cast<integer_interface *>(qApp); emit myApp->libraryLogged(message); }as suggested by @JonB
PS
@JonB doing as you suggested as sanity check with the following linesinteger_interface *myApp = qobject_cast<integer_interface *>(qApp); Q_ASSERT(myApp);gives a bunch of errors not sure I understand:
logger_widget.h:42:14: C++ requires a type specifier for all declarationslogger_widget.h:42:5: Expected ')' 0:0: :42:5: note: to match this '(' logger_widget.h:42:14: Duplicate member 'myApp' logger_widget.h:41:24: previous declaration is here@Gaetano03
Look, can you please show yourmain()function now. I have a funny feeling your still haveQApplication a(argc, argv);there, and what do you think you actually need instead of that? -
I have it declared and instantiated both in the logger_widget.h class among the private members
private: Ui::logger_widget *ui; integer::logger::errors err_init; integer::logger::integer_logger& logger = integer::logger::integer_logger::get_instance(); integer_interface *myApp = qobject_cast<integer_interface *>(qApp);and in the static log function
void log(std::string message) { integer_interface *myApp = qobject_cast<integer_interface *>(qApp); emit myApp->libraryLogged(message); }as suggested by @JonB
PS
@JonB doing as you suggested as sanity check with the following linesinteger_interface *myApp = qobject_cast<integer_interface *>(qApp); Q_ASSERT(myApp);gives a bunch of errors not sure I understand:
logger_widget.h:42:14: C++ requires a type specifier for all declarationslogger_widget.h:42:5: Expected ')' 0:0: :42:5: note: to match this '(' logger_widget.h:42:14: Duplicate member 'myApp' logger_widget.h:41:24: previous declaration is here@Gaetano03 said in Add to Qt GUI logger functionality:
integer_interface *myApp = qobject_cast<integer_interface *>(qApp); Q_ASSERT(myApp);If that is in a
.hwhere you are declaring member variables in a class definition you cannot add arbitrary C++ statements to execute..... Put theqobject_cast<>in the constructor, where you can verify it. -
@Gaetano03
Look, can you please show yourmain()function now. I have a funny feeling your still haveQApplication a(argc, argv);there, and what do you think you actually need instead of that? -
@JonB
you have the right funny feeling, just realized how silly I was.Everything works fine now and I get stuff printed on my QPlainText, at least for now XD.
Thanks a lot, really!
I really appreciate
@Gaetano03
Yeah, do you get the point? You can subclassQApplicationto add whatever you want, but then you must create aSubclassedApplicationnot the original base classQApplicationto use it. Just like any other subclassing.qApp()macro returnsQApplication *-type pointer, for whatever (single)QApplicationinstance has been created. If you derived and created the derived instance,qAppwon't return that derived type (though it will return the correct derived instance). So to call methods/access variables you defined in your subclass that's why weqobject_cast<SubclassedApplication *>(qApp). -
@Gaetano03
Yeah, do you get the point? You can subclassQApplicationto add whatever you want, but then you must create aSubclassedApplicationnot the original base classQApplicationto use it. Just like any other subclassing.qApp()macro returnsQApplication *-type pointer, for whatever (single)QApplicationinstance has been created. If you derived and created the derived instance,qAppwon't return that derived type (though it will return the correct derived instance). So to call methods/access variables you defined in your subclass that's why weqobject_cast<SubclassedApplication *>(qApp).@JonB
Yes I got the point, thanks also for this explanation!! That helps a lot understanding what I am doing behind the lines!!!I have to admit that I worked so much on the library that I forgot for a while a main calling it and launching the app was even existing XD
