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

Time：12-04

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

CodePudding user response：

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);

Page link：https//www.codepudding.com/database/631870.html

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