如何将 Qt signal/slot 名称存储到数据结构中？

Question

我想将信号或槽的名称存储到容器中，以便我可以检索它并与之建立连接。

一种方法是hack the SIGNAL/SLOT macro and store the signal/slot's name as strings, and then use the the old connect syntax像这样建立连接

void connect(QObject *dst, QString slot)
{
    connect(this, SIGNAL(foo(void)), dst, slot.toLocal8Bit().data());
    // void foo(void) is a member signal of "this" and is known 
    // at compile time
    // but "dst" and "slot" are not known until runtime.
}

然而，这对我来说似乎有点太老套了。

我知道有another syntax for connect and there is also an object type for signal/slots, which implies a different and (potentially) less hacky solution. (note that this is not the new signal/slot syntax in Qt5)

但问题是，QMetaMethod 没有记录在案的构造函数，它似乎是可复制构造的。

还有一个问题，当signal/slots的名字是动态的时候，你如何建立联系？

我的编码环境是 Qt4 和 gcc 4.3.3 gnu++98，所以需要 Qt5 和 C++11 的解决方案虽然受欢迎，但对我来说用处不大。

Answer 1

2 个解决方案，我正在寻找第 3 个。

用于示例的简单 class：

#include <QObject>
#include <QDebug>

class MyClass : public QObject
{
    Q_OBJECT
public:
    MyClass() : QObject() { }

    void fireSignals()
    {
        qDebug() << "signal1 :" ;
        emit signal1();
        qDebug() << "signal2 :" ;
        emit signal2();
        qDebug() << "signal3 :" ;
        emit signal3(3);
    }

public slots:
    void slot1() { qDebug() << "slot1"; }
    void slot2() { qDebug() << "slot2"; }
    void slot3() { qDebug() << "slot3"; }
    void slot4(int i) { qDebug() << "slot4" << i; }
signals:
    void signal1();
    void signal2();
    void signal3(int);
};

Qt4/C++98:

我没有 Qt4，请告诉我这个解决方案是否有效。

使用 Qt 5.5、mingw 4.9.2、-std=c++98 测试

它依赖于将信号或插槽名称转换为其索引，然后转换为关联的 QMetaMethod。

注意：可以改为存储 QMetaMethod 个对象。这种方法更安全，因为插槽存在的检查发生得更早，但是在创建 QMap 之前需要一个 MyClass 实例，同时存储插槽名称更灵活。

// Get the index of a method, using obj's metaobject
QMetaMethod fetchIndexOfMethod(QObject* obj, const char* name)
{
    const QMetaObject* meta_object = obj->metaObject();
    QByteArray normalized_name = QMetaObject::normalizedSignature(name);
    int index = meta_object->indexOfMethod(normalized_name.constData());
    Q_ASSERT(index != -1);
    return meta_object->method(index);
}

// A QObject::connect wrapper
QMetaObject::Connection dynamicConnection(QObject* source,
                                          const char* signal_name,
                                          QObject* dest,
                                          const char* slot_name)
{
   return QObject::connect(source, fetchIndexOfMethod(source, signal_name),
                           dest, fetchIndexOfMethod(dest, slot_name));
}

void first_way()
{
    qDebug() << "\nFirst way:";
    QMap<QString, const char*> my_slots;
    my_slots["id_slot1"] = "slot1()";
    my_slots["id_slot2"] = "slot2()";
    my_slots["id_slot3"] = "slot3()";
    my_slots["id_slot4"] = "slot4(int)"; // slots with different signatures in the same container

    MyClass object;
    dynamicConnection(&object, "signal1()", &object, my_slots.value("id_slot1"));
    dynamicConnection(&object, "signal1()", &object, my_slots.value("id_slot2"));
    dynamicConnection(&object, "signal2()", &object, my_slots.value("id_slot3"));
    dynamicConnection(&object, "signal3(int)", &object, my_slots.value("id_slot4"));

    object.fireSignals();
}

Qt5/C++14:

使用 Qt 5.5、mingw 4.9.2、-std=c++14 测试

这个正在使用指向成员函数的指针。它是类型安全的，因此您不能在同一容器中使用具有不同签名的插槽。

template <typename T, typename R, typename ...Args>
struct PointerToMemberHelper
{
    using type = R (T::*)(Args...);
};

void second_way()
{
    qDebug() << "\nSecond way:";

    using MPTR_void = PointerToMemberHelper<MyClass, void>::type;
    using MPTR_int = PointerToMemberHelper<MyClass, void, int>::type;

    QMap<QString, MPTR_void> my_slots({{"id_slot1", MyClass::slot1},
                                       {"id_slot2", MyClass::slot2},
                                       {"id_slot3", MyClass::slot3}});

    MyClass object;
    QObject::connect(&object, MyClass::signal1, &object, my_slots.value("id_slot1"));
    QObject::connect(&object, MyClass::signal1, &object, my_slots.value("id_slot2"));
    QObject::connect(&object, MyClass::signal2, &object, my_slots.value("id_slot3"));

    MPTR_int my_int_slot = MyClass::slot4; // or auto my_int_slot = ...
    QObject::connect(&object, MyClass::signal3, &object, my_int_slot);

    object.fireSignals();
}

目前正在尝试基于 lambda 和 QMetaObject::invokeMethod 使第三个解决方案起作用 - 但它不会比第二个解决方案做得更多。

如何将 Qt signal/slot 名称存储到数据结构中？

How to store Qt signal/slot names to a data structure?

c++

qt

qt4