如何将插槽作为参数传递

Posted 2023-02-17

【中文标题】如何将插槽作为参数传递

【英文标题】：How to pass a slot as an argument

【发布时间】：2016-08-12 13:49:11

【问题描述】：

我正在使用 Qt 5.7，并且我有一个行为类似于 QMenuBar 的组件。该组件有两种方法，一种称为addMenu(QPushButton* menu)，用于添加条形菜单，另一种称为addMenuItem(QPushButton* menu, QString item, const char *slot)，用于添加构成条形菜单之一的项目。在第二个方法中，我调用 QMenu 的 addAction 方法，并且必须向它传递两个参数：项目名称和触发项目时将运行的插槽。我的问题是怎么做。 我进行了搜索（请参阅here），我发现 QT 将插槽视为const char *，但是当我尝试使用此方法签名编译我的程序时，它给出了错误，说明没有为此注册 operator()输入。

我的代码：

GMInternalMenu::addMenuItem(QPushButton *menu, QString menuItem, const char* slot)
    QMenu *dropdown = mapa->value(menu);
    dropdown->addAction(menuItem, slot);

使用方法：

ui->imMenu->addMenuItem(someButton, "Some action", SLOT(close()));

输出错误： （也在pastebin上）

In file included from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtGui/qwindowdefs.h:43:0,
                 from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/qwidget.h:43,
                 from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/qmenu.h:43,
                 from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/QMenu:1,
                 from ../Project/mymenu.h:4,
                 from ../Project/mymenu.cpp:1:
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobject.h: In instantiation of 'static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (QAction::*)(bool); Func2 = const char*; typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type = QMetaObject::Connection; typename QtPrivate::FunctionPointer<Func>::Object = QAction]':
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobject.h:293:74:   required from 'static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, Func2) [with Func1 = void (QAction::*)(bool); Func2 = const char*; typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type = QMetaObject::Connection; typename QtPrivate::FunctionPointer<Func>::Object = QAction]'
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/qmenu.h:120:9:   required from 'QAction* QMenu::addAction(const QString&, Func1, const QKeySequence&) [with Func1 = const char*]'
../Project/mymenu.cpp:35:39:   required from here
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qglobal.h:746:47: error: static assertion failed: Signal and slot arguments are not compatible.
 #define Q_STATIC_ASSERT_X(Condition, Message) static_assert(bool(Condition), Message)
                                               ^
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobject.h:306:9: note: in expansion of macro 'Q_STATIC_ASSERT_X'
         Q_STATIC_ASSERT_X((FunctorArgumentCount >= 0),
         ^
In file included from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobjectdefs.h:50:0,
                 from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtGui/qwindowdefs.h:44,
                 from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/qwidget.h:43,
                 from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/qmenu.h:43,
                 from C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/QMenu:1,
                 from ../Project/mymenu.h:4,
                 from ../Project/mymenu.cpp:1:
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobjectdefs_impl.h: In instantiation of 'struct QtPrivate::FunctorReturnType<const char*, QtPrivate::List<> >':
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobject.h:309:158:   required from 'static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (QAction::*)(bool); Func2 = const char*; typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type = QMetaObject::Connection; typename QtPrivate::FunctionPointer<Func>::Object = QAction]'
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobject.h:293:74:   required from 'static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, Func2) [with Func1 = void (QAction::*)(bool); Func2 = const char*; typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == (-1)), QMetaObject::Connection>::Type = QMetaObject::Connection; typename QtPrivate::FunctionPointer<Func>::Object = QAction]'
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtWidgets/qmenu.h:120:9:   required from 'QAction* QMenu::addAction(const QString&, Func1, const QKeySequence&) [with Func1 = const char*]'
../Project/mymenu.cpp:35:39:   required from here
C:/Qt/Qt5.7.0/5.7/mingw53_32/include/QtCore/qobjectdefs_impl.h:632:78: error: request for member 'operator()' in 'QtPrivate::FunctorReturnType<Functor, QtPrivate::List<Tail ...> >::dummy<const char*>()', which is of non-class type 'const char*'
         typedef decltype(dummy<Functor>().operator()((dummy<ArgList>())...)) Value;

【问题讨论】：

你使用的是Qt4还是Qt5？

另外，请将错误粘贴到您的问题中，有些人无法访问 pastebin.com ;)

【参考方案1】：

这是您尝试使用的QMenu::addAction 方法的声明：

QAction* addAction(const QString &text, 
                   const QObject *receiver, 
                   const char *member, 
                   const QKeySequence &shortcut = 0);

如您所见，您缺少receiver 参数，这是将接收信号的对象。

从你的代码中，我猜你应该有类似的东西：

GMInternalMenu::addMenuItem(QPushButton *menu, QString menuItem, 
                            QObject *receiver, const char* slot)
    QMenu *dropdown = mapa->value(menu);
    dropdown->addAction(menuItem, receiver, slot);

然后当你使用它时：

ui->imMenu->addMenuItem(someButton, "Some action", this, SLOT(close()));
//                                                 ^^^^
//                 Maybe something else... I do not know
//                 which object should receive the signal.