TechQA.

My QT connect works from parent to child, but not vice versa

132 views Asked by At

I am making a QT application. I have a MainWindow1 class and a FirstTab class. The MainWindow1 class is a QMainWindow and inside I created this signal ->

mainwindow1.h

signals:
    void loadDateSig(QString strDate);

And in FirstTab I created this slot->

FirstTab.h

public slots:
    void loadDate(QString date);

Q_Object is defined in both MainWindow1 and in FirstTab. Now in my MainWindow1 constructor, this is how I start ->

mainwindow1.cpp

MainWindow1::MainWindow1()
    : mainWidget(new QTabWidget) {
    
    setCentralWidget(mainWidget);
    mainWidget->addTab(new FirstTab(mainWidget), "First");
    createActions();
    createStatusBar();

And below that, I start making some connections. I connect a few items to change the status that the document was modified. You can see them here, and these work with no issues ->

connect(mainWidget->findChild<QTimeEdit *>("timeEdit"), &QTimeEdit::editingFinished,
        this, &MainWindow1::documentWasModified);
connect(mainWidget->findChild<QDateEdit *>("dateEdit"), &QTimeEdit::editingFinished,
        this, &MainWindow1::documentWasModified);
connect(mainWidget->findChild<QLineEdit *>("shooterEdit"), &QLineEdit::textEdited,
        this, &MainWindow1::documentWasModified);
connect(mainWidget->findChild<QLineEdit *>("recorderEdit"), &QLineEdit::textEdited,
        this, &MainWindow1::documentWasModified);
connect(mainWidget->findChild<QDoubleSpinBox *>("tempCSpin"), &QDoubleSpinBox::editingFinished,
        this, &MainWindow1::documentWasModified);
connect(mainWidget->findChild<QDoubleSpinBox *>("tempFSpin"), &QDoubleSpinBox::editingFinished,
        this, &MainWindow1::documentWasModified);

Now I try to connect my loadDateSig and loadDate. I have tried both creating the connect in the child, and in the parent class. But both give me an error. I tried to connect similar to how I connected previosly ->

connect(this, &MainWindow1::loadDateSig, mainWidget->findChild<QWidget *>("tab1"), &FirstTab::loadDate);

However, this doesn't seem to work. I get these errors ->

====================[ Build | all | Debug ]=====================================
"E:\Program Files (x86)\CLion 2022.2.1\bin\cmake\win\bin\cmake.exe" --build E:\Projects\Galvion\cmake-build-debug --target all -j 9
[1/4] Automatic MOC and UIC for target Galvion
[2/3] Building CXX object CMakeFiles/Galvion.dir/mainwindow1.cpp.obj
FAILED: CMakeFiles/Galvion.dir/mainwindow1.cpp.obj 
E:\PROGRA~1\CLION2~1.1\bin\mingw\bin\G__~1.EXE -DMINGW_HAS_SECURE_API=1 -DQT_CORE_LIB -DQT_GUI_LIB -DQT_WIDGETS_LIB -DUNICODE -DWIN32 -DWIN64 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -D_UNICODE -D_WIN64 -IE:/Projects/Galvion/cmake-build-debug -IE:/Projects/Galvion -IE:/Projects/Galvion/cmake-build-debug/Galvion_autogen/include -isystem C:/Qt/6.4.1/mingw_64/include/QtCore -isystem C:/Qt/6.4.1/mingw_64/include -isystem C:/Qt/6.4.1/mingw_64/mkspecs/win32-g++ -isystem C:/Qt/6.4.1/mingw_64/include/QtGui -isystem C:/Qt/6.4.1/mingw_64/include/QtWidgets -g -MD -MT CMakeFiles/Galvion.dir/mainwindow1.cpp.obj -MF CMakeFiles\Galvion.dir\mainwindow1.cpp.obj.d -o CMakeFiles/Galvion.dir/mainwindow1.cpp.obj -c E:/Projects/Galvion/mainwindow1.cpp
E:/Projects/Galvion/mainwindow1.cpp: In constructor 'MainWindow1::MainWindow1()':
E:/Projects/Galvion/mainwindow1.cpp:26:12: error: no matching function for call to 'MainWindow1::connect(MainWindow1*, void (MainWindow1::*)(QString), QWidget*, void (FirstTab::*)(QString))'
   26 |     connect(this, &MainWindow1::loadDateSig, mainWidget->findChild<QWidget *>("tab1"), &FirstTab::loadDate);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QTWidgets:3,
                 from E:/Projects/Galvion/mainwindow1.h:7,
                 from E:/Projects/Galvion/mainwindow1.cpp:1:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:201:43: note: candidate: 'static QMetaObject::Connection QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const typename QtPrivate::FunctionPointer<Func2>::Object*, Func2, Qt::ConnectionType) [with Func1 = void (MainWindow1::*)(QString); Func2 = void (FirstTab::*)(QString); typename QtPrivate::FunctionPointer<Func>::Object = MainWindow1; typename QtPrivate::FunctionPointer<Func2>::Object = FirstTab]' (near match)
  201 |     static inline QMetaObject::Connection connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal,
      |                                           ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:201:43: note:   conversion of argument 3 would be ill-formed:
E:/Projects/Galvion/mainwindow1.cpp:26:78: error: invalid conversion from 'QWidget*' to 'const Object*' {aka 'const FirstTab*'} [-fpermissive]
   26 |     connect(this, &MainWindow1::loadDateSig, mainWidget->findChild<QWidget *>("tab1"), &FirstTab::loadDate);
      |                                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
      |                                                                              |
      |                                                                              QWidget*
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QTWidgets:3,
                 from E:/Projects/Galvion/mainwindow1.h:7,
                 from E:/Projects/Galvion/mainwindow1.cpp:1:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:233:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<((int)(QtPrivate::FunctionPointer<Func2>::ArgumentCount) >= 0), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, Func2)'
  233 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, Func2 slot)
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:233:13: note:   template argument deduction/substitution failed:
E:/Projects/Galvion/mainwindow1.cpp:26:12: note:   candidate expects 3 arguments, 4 provided
   26 |     connect(this, &MainWindow1::loadDateSig, mainWidget->findChild<QWidget *>("tab1"), &FirstTab::loadDate);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QTWidgets:3,
                 from E:/Projects/Galvion/mainwindow1.h:7,
                 from E:/Projects/Galvion/mainwindow1.cpp:1:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:242:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<(((int)(QtPrivate::FunctionPointer<Func2>::ArgumentCount) >= 0) && (! QtPrivate::FunctionPointer<Func2>::IsPointerToMemberFunction)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType)'
  242 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, const QObject *context, Func2 slot,
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:242:13: note:   template argument deduction/substitution failed:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h: In substitution of 'template<class Func1, class Func2> static typename std::enable_if<(((int)(QtPrivate::FunctionPointer<Func2>::ArgumentCount) >= 0) && (! QtPrivate::FunctionPointer<Func2>::IsPointerToMemberFunction)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (MainWindow1::*)(QString); Func2 = void (FirstTab::*)(QString)]':
E:/Projects/Galvion/mainwindow1.cpp:26:12:   required from here
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:242:13: error: no type named 'type' in 'struct std::enable_if<false, QMetaObject::Connection>'
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:276:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<((QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1) && (! is_convertible_v<Func2, const char*>)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, Func2)'
  276 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, Func2 slot)
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:276:13: note:   template argument deduction/substitution failed:
E:/Projects/Galvion/mainwindow1.cpp:26:12: note:   candidate expects 3 arguments, 4 provided
   26 |     connect(this, &MainWindow1::loadDateSig, mainWidget->findChild<QWidget *>("tab1"), &FirstTab::loadDate);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QTWidgets:3,
                 from E:/Projects/Galvion/mainwindow1.h:7,
                 from E:/Projects/Galvion/mainwindow1.cpp:1:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:287:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<((QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1) && (! is_convertible_v<Func2, const char*>)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType)'
  287 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, const QObject *context, Func2 slot,
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:287:13: note:   template argument deduction/substitution failed:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h: In substitution of 'template<class Func1, class Func2> static typename std::enable_if<((QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1) && (! is_convertible_v<Func2, const char*>)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (MainWindow1::*)(QString); Func2 = void (FirstTab::*)(QString)]':
E:/Projects/Galvion/mainwindow1.cpp:26:12:   required from here
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:287:13: error: no type named 'type' in 'struct std::enable_if<false, QMetaObject::Connection>'
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:181:36: note: candidate: 'static QMetaObject::Connection QObject::connect(const QObject*, const char*, const QObject*, const char*, Qt::ConnectionType)'
  181 |     static QMetaObject::Connection connect(const QObject *sender, const char *signal,
      |                                    ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:181:79: note:   no known conversion for argument 2 from 'void (MainWindow1::*)(QString)' to 'const char*'
  181 |     static QMetaObject::Connection connect(const QObject *sender, const char *signal,
      |                                                                   ~~~~~~~~~~~~^~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:184:36: note: candidate: 'static QMetaObject::Connection QObject::connect(const QObject*, const QMetaMethod&, const QObject*, const QMetaMethod&, Qt::ConnectionType)'
  184 |     static QMetaObject::Connection connect(const QObject *sender, const QMetaMethod &signal,
      |                                    ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:184:86: note:   no known conversion for argument 2 from 'void (MainWindow1::*)(QString)' to 'const QMetaMethod&'
  184 |     static QMetaObject::Connection connect(const QObject *sender, const QMetaMethod &signal,
      |                                                                   ~~~~~~~~~~~~~~~~~~~^~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:432:32: note: candidate: 'QMetaObject::Connection QObject::connect(const QObject*, const char*, const char*, Qt::ConnectionType) const'
  432 | inline QMetaObject::Connection QObject::connect(const QObject *asender, const char *asignal,
      |                                ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:432:85: note:   no known conversion for argument 2 from 'void (MainWindow1::*)(QString)' to 'const char*'
  432 | inline QMetaObject::Connection QObject::connect(const QObject *asender, const char *asignal,
      |                                                                         ~~~~~~~~~~~~^~~~~~~
ninja: build stopped: subcommand failed.

Could anyone help me figure out why this happens?

I tried to create the connect in the FirstTab class. Changing the parent in mainwindow1.cpp form mainWidget parent to this so the child class can access the signal ->

mainWidget->addTab(new FirstTab(this), "First");

And then I create this connect in FirstTab.cpp ->

connect(parent, &MainWindow1::loadDateSig, this, &FirstTab::loadDate);

I get this error when trying to build ->

====================[ Build | all | Debug ]=====================================
"E:\Program Files (x86)\CLion 2022.2.1\bin\cmake\win\bin\cmake.exe" --build E:\Projects\Galvion\cmake-build-debug --target all -j 9
[1/5] Automatic MOC and UIC for target Galvion
[2/4] Building CXX object CMakeFiles/Galvion.dir/FirstTab.cpp.obj
FAILED: CMakeFiles/Galvion.dir/FirstTab.cpp.obj 
E:\PROGRA~1\CLION2~1.1\bin\mingw\bin\G__~1.EXE -DMINGW_HAS_SECURE_API=1 -DQT_CORE_LIB -DQT_GUI_LIB -DQT_WIDGETS_LIB -DUNICODE -DWIN32 -DWIN64 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -D_UNICODE -D_WIN64 -IE:/Projects/Galvion/cmake-build-debug -IE:/Projects/Galvion -IE:/Projects/Galvion/cmake-build-debug/Galvion_autogen/include -isystem C:/Qt/6.4.1/mingw_64/include/QtCore -isystem C:/Qt/6.4.1/mingw_64/include -isystem C:/Qt/6.4.1/mingw_64/mkspecs/win32-g++ -isystem C:/Qt/6.4.1/mingw_64/include/QtGui -isystem C:/Qt/6.4.1/mingw_64/include/QtWidgets -g -MD -MT CMakeFiles/Galvion.dir/FirstTab.cpp.obj -MF CMakeFiles\Galvion.dir\FirstTab.cpp.obj.d -o CMakeFiles/Galvion.dir/FirstTab.cpp.obj -c E:/Projects/Galvion/FirstTab.cpp
E:/Projects/Galvion/FirstTab.cpp: In constructor 'FirstTab::FirstTab(QWidget*)':
E:/Projects/Galvion/FirstTab.cpp:82:12: error: no matching function for call to 'FirstTab::connect(QWidget*&, void (MainWindow1::*)(QString), FirstTab*, void (FirstTab::*)(QString))'
   82 |     connect(parent, &MainWindow1::loadDateSig, this, &FirstTab::loadDate);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgets:3,
                 from E:/Projects/Galvion/FirstTab.h:7,
                 from E:/Projects/Galvion/FirstTab.cpp:5:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:201:43: note: candidate: 'static QMetaObject::Connection QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const typename QtPrivate::FunctionPointer<Func2>::Object*, Func2, Qt::ConnectionType) [with Func1 = void (MainWindow1::*)(QString); Func2 = void (FirstTab::*)(QString); typename QtPrivate::FunctionPointer<Func>::Object = MainWindow1; typename QtPrivate::FunctionPointer<Func2>::Object = FirstTab]' (near match)
  201 |     static inline QMetaObject::Connection connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal,
      |                                           ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:201:43: note:   conversion of argument 1 would be ill-formed:
E:/Projects/Galvion/FirstTab.cpp:82:13: error: invalid conversion from 'QWidget*' to 'const Object*' {aka 'const MainWindow1*'} [-fpermissive]
   82 |     connect(parent, &MainWindow1::loadDateSig, this, &FirstTab::loadDate);
      |             ^~~~~~
      |             |
      |             QWidget*
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgets:3,
                 from E:/Projects/Galvion/FirstTab.h:7,
                 from E:/Projects/Galvion/FirstTab.cpp:5:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:233:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<((int)(QtPrivate::FunctionPointer<Func2>::ArgumentCount) >= 0), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, Func2)'
  233 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, Func2 slot)
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:233:13: note:   template argument deduction/substitution failed:
E:/Projects/Galvion/FirstTab.cpp:82:12: note:   candidate expects 3 arguments, 4 provided
   82 |     connect(parent, &MainWindow1::loadDateSig, this, &FirstTab::loadDate);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgets:3,
                 from E:/Projects/Galvion/FirstTab.h:7,
                 from E:/Projects/Galvion/FirstTab.cpp:5:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:242:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<(((int)(QtPrivate::FunctionPointer<Func2>::ArgumentCount) >= 0) && (! QtPrivate::FunctionPointer<Func2>::IsPointerToMemberFunction)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType)'
  242 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, const QObject *context, Func2 slot,
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:242:13: note:   template argument deduction/substitution failed:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h: In substitution of 'template<class Func1, class Func2> static typename std::enable_if<(((int)(QtPrivate::FunctionPointer<Func2>::ArgumentCount) >= 0) && (! QtPrivate::FunctionPointer<Func2>::IsPointerToMemberFunction)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (MainWindow1::*)(QString); Func2 = void (FirstTab::*)(QString)]':
E:/Projects/Galvion/FirstTab.cpp:82:12:   required from here
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:242:13: error: no type named 'type' in 'struct std::enable_if<false, QMetaObject::Connection>'
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:276:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<((QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1) && (! is_convertible_v<Func2, const char*>)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, Func2)'
  276 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, Func2 slot)
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:276:13: note:   template argument deduction/substitution failed:
E:/Projects/Galvion/FirstTab.cpp:82:12: note:   candidate expects 3 arguments, 4 provided
   82 |     connect(parent, &MainWindow1::loadDateSig, this, &FirstTab::loadDate);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from C:/Qt/6.4.1/mingw_64/include/QtCore/qabstractanimation.h:7,
                 from C:/Qt/6.4.1/mingw_64/include/QtCore/QtCore:10,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgetsDepends:3,
                 from C:/Qt/6.4.1/mingw_64/include/QtWidgets/QtWidgets:3,
                 from E:/Projects/Galvion/FirstTab.h:7,
                 from E:/Projects/Galvion/FirstTab.cpp:5:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:287:13: note: candidate: 'template<class Func1, class Func2> static typename std::enable_if<((QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1) && (! is_convertible_v<Func2, const char*>)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType)'
  287 |             connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, const QObject *context, Func2 slot,
      |             ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:287:13: note:   template argument deduction/substitution failed:
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h: In substitution of 'template<class Func1, class Func2> static typename std::enable_if<((QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1) && (! is_convertible_v<Func2, const char*>)), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (MainWindow1::*)(QString); Func2 = void (FirstTab::*)(QString)]':
E:/Projects/Galvion/FirstTab.cpp:82:12:   required from here
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:287:13: error: no type named 'type' in 'struct std::enable_if<false, QMetaObject::Connection>'
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:181:36: note: candidate: 'static QMetaObject::Connection QObject::connect(const QObject*, const char*, const QObject*, const char*, Qt::ConnectionType)'
  181 |     static QMetaObject::Connection connect(const QObject *sender, const char *signal,
      |                                    ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:181:79: note:   no known conversion for argument 2 from 'void (MainWindow1::*)(QString)' to 'const char*'
  181 |     static QMetaObject::Connection connect(const QObject *sender, const char *signal,
      |                                                                   ~~~~~~~~~~~~^~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:184:36: note: candidate: 'static QMetaObject::Connection QObject::connect(const QObject*, const QMetaMethod&, const QObject*, const QMetaMethod&, Qt::ConnectionType)'
  184 |     static QMetaObject::Connection connect(const QObject *sender, const QMetaMethod &signal,
      |                                    ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:184:86: note:   no known conversion for argument 2 from 'void (MainWindow1::*)(QString)' to 'const QMetaMethod&'
  184 |     static QMetaObject::Connection connect(const QObject *sender, const QMetaMethod &signal,
      |                                                                   ~~~~~~~~~~~~~~~~~~~^~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:432:32: note: candidate: 'QMetaObject::Connection QObject::connect(const QObject*, const char*, const char*, Qt::ConnectionType) const'
  432 | inline QMetaObject::Connection QObject::connect(const QObject *asender, const char *asignal,
      |                                ^~~~~~~
C:/Qt/6.4.1/mingw_64/include/QtCore/qobject.h:432:85: note:   no known conversion for argument 2 from 'void (MainWindow1::*)(QString)' to 'const char*'
  432 | inline QMetaObject::Connection QObject::connect(const QObject *asender, const char *asignal,
      |                                                                         ~~~~~~~~~~~~^~~~~~~
[3/4] Building CXX object CMakeFiles/Galvion.dir/mainwindow1.cpp.obj
ninja: build stopped: subcommand failed.

Edit: I forgot to mention that the QWidget FirstTab has and object name, so it should be finding it correctly

c++ qt qt6 qt-connection
Original Q&A
1

There are 1 answers

1
m7913d On BEST ANSWER

Reading the error message may be tricky sometimes. The key is:

invalid conversion from 'QWidget*' to 'const Object*' {aka 'const FirstTab*'}

C++ doesn't allow automatic conversion from a base class (QWidget) to a derived class (FirstTab) as not all QWidgets are FirstTabs. So you should perform the conversion yourself. In general this could be safely achieved using qobject_cast, but in this case requesting a FirstTab instance instead of a general QWidget seems to be the best approach:

connect(this, &MainWindow1::loadDateSig, mainWidget->findChild<FirstTab *>("tab1"), &FirstTab::loadDate);

Related Questions in C++

Related Questions in QT

Related Questions in QT6

Related Questions in QT-CONNECTION

Popular Questions

Popular Tags

javascript python java c# php android html jquery c++ css ios sql mysql r reactjs node.js arrays c asp.net json python-3.x ruby-on-rails .net sql-server swift django angular objective-c pandas excel

Trending Questions