Qt--QMetaObject

QMetaObject接口分析

上一节中我们概述了Meta-Object Model的架构，它通过提供了一个QObject的基类，使用Q_OBJECT宏，这样moc编译器就会自动帮我们生成带有QMetaObject记录了元信息的源码。

这节我们看下QMetaObject提供了哪些接口去获取或使用这些元信息

上源代码：

struct Q_CORE_EXPORT QMetaObject
{
    class Connection;
    const char *className() const;
    const QMetaObject *superClass() const;

    bool inherits(const QMetaObject *metaObject) const Q_DECL_NOEXCEPT;
    QObject *cast(QObject *obj) const;
    const QObject *cast(const QObject *obj) const;

#ifndef QT_NO_TRANSLATION
    QString tr(const char *s, const char *c, int n = -1) const;
#endif // QT_NO_TRANSLATION

    int methodOffset() const;
    int enumeratorOffset() const;
    int propertyOffset() const;
    int classInfoOffset() const;

    int constructorCount() const;
    int methodCount() const;
    int enumeratorCount() const;
    int propertyCount() const;
    int classInfoCount() const;

    int indexOfConstructor(const char *constructor) const;
    int indexOfMethod(const char *method) const;
    int indexOfSignal(const char *signal) const;
    int indexOfSlot(const char *slot) const;
    int indexOfEnumerator(const char *name) const;
    int indexOfProperty(const char *name) const;
    int indexOfClassInfo(const char *name) const;

    QMetaMethod constructor(int index) const;
    QMetaMethod method(int index) const;
    QMetaEnum enumerator(int index) const;
    QMetaProperty property(int index) const;
    QMetaClassInfo classInfo(int index) const;
    QMetaProperty userProperty() const;

    static bool checkConnectArgs(const char *signal, const char *method);
    static bool checkConnectArgs(const QMetaMethod &signal,
                                 const QMetaMethod &method);
    static QByteArray normalizedSignature(const char *method);
    static QByteArray normalizedType(const char *type);

    // internal index-based connect
    static Connection connect(const QObject *sender, int signal_index,
                        const QObject *receiver, int method_index,
                        int type = 0, int *types = Q_NULLPTR);
    // internal index-based disconnect
    static bool disconnect(const QObject *sender, int signal_index,
                           const QObject *receiver, int method_index);
    static bool disconnectOne(const QObject *sender, int signal_index,
                              const QObject *receiver, int method_index);
    // internal slot-name based connect
    static void connectSlotsByName(QObject *o);

    // internal index-based signal activation
    static void activate(QObject *sender, int signal_index, void **argv);
    static void activate(QObject *sender, const QMetaObject *, int local_signal_index, void **argv);
    static void activate(QObject *sender, int signal_offset, int local_signal_index, void **argv);

    static bool invokeMethod(QObject *obj, const char *member,
                             Qt::ConnectionType,
                             QGenericReturnArgument ret,
                             QGenericArgument val0 = QGenericArgument(Q_NULLPTR),
                             QGenericArgument val1 = QGenericArgument(),
                             QGenericArgument val2 = QGenericArgument(),
                             QGenericArgument val3 = QGenericArgument(),
                             QGenericArgument val4 = QGenericArgument(),
                             QGenericArgument val5 = QGenericArgument(),
                             QGenericArgument val6 = QGenericArgument(),
                             QGenericArgument val7 = QGenericArgument(),
                             QGenericArgument val8 = QGenericArgument(),
                             QGenericArgument val9 = QGenericArgument());

    static inline bool invokeMethod(QObject *obj, const char *member,
                             QGenericReturnArgument ret,
                             QGenericArgument val0 = QGenericArgument(Q_NULLPTR),
                             QGenericArgument val1 = QGenericArgument(),
                             QGenericArgument val2 = QGenericArgument(),
                             QGenericArgument val3 = QGenericArgument(),
                             QGenericArgument val4 = QGenericArgument(),
                             QGenericArgument val5 = QGenericArgument(),
                             QGenericArgument val6 = QGenericArgument(),
                             QGenericArgument val7 = QGenericArgument(),
                             QGenericArgument val8 = QGenericArgument(),
                             QGenericArgument val9 = QGenericArgument())
    {
        return invokeMethod(obj, member, Qt::AutoConnection, ret, val0, val1, val2, val3,
                val4, val5, val6, val7, val8, val9);
    }

    static inline bool invokeMethod(QObject *obj, const char *member,
                             Qt::ConnectionType type,
                             QGenericArgument val0 = QGenericArgument(Q_NULLPTR),
                             QGenericArgument val1 = QGenericArgument(),
                             QGenericArgument val2 = QGenericArgument(),
                             QGenericArgument val3 = QGenericArgument(),
                             QGenericArgument val4 = QGenericArgument(),
                             QGenericArgument val5 = QGenericArgument(),
                             QGenericArgument val6 = QGenericArgument(),
                             QGenericArgument val7 = QGenericArgument(),
                             QGenericArgument val8 = QGenericArgument(),
                             QGenericArgument val9 = QGenericArgument())
    {
        return invokeMethod(obj, member, type, QGenericReturnArgument(), val0, val1, val2,
                                 val3, val4, val5, val6, val7, val8, val9);
    }

    static inline bool invokeMethod(QObject *obj, const char *member,
                             QGenericArgument val0 = QGenericArgument(Q_NULLPTR),
                             QGenericArgument val1 = QGenericArgument(),
                             QGenericArgument val2 = QGenericArgument(),
                             QGenericArgument val3 = QGenericArgument(),
                             QGenericArgument val4 = QGenericArgument(),
                             QGenericArgument val5 = QGenericArgument(),
                             QGenericArgument val6 = QGenericArgument(),
                             QGenericArgument val7 = QGenericArgument(),
                             QGenericArgument val8 = QGenericArgument(),
                             QGenericArgument val9 = QGenericArgument())
    {
        return invokeMethod(obj, member, Qt::AutoConnection, QGenericReturnArgument(), val0,
                val1, val2, val3, val4, val5, val6, val7, val8, val9);
    }

    QObject *newInstance(QGenericArgument val0 = QGenericArgument(Q_NULLPTR),
                         QGenericArgument val1 = QGenericArgument(),
                         QGenericArgument val2 = QGenericArgument(),
                         QGenericArgument val3 = QGenericArgument(),
                         QGenericArgument val4 = QGenericArgument(),
                         QGenericArgument val5 = QGenericArgument(),
                         QGenericArgument val6 = QGenericArgument(),
                         QGenericArgument val7 = QGenericArgument(),
                         QGenericArgument val8 = QGenericArgument(),
                         QGenericArgument val9 = QGenericArgument()) const;

    enum Call {
        InvokeMetaMethod,
        ReadProperty,
        WriteProperty,
        ResetProperty,
        QueryPropertyDesignable,
        QueryPropertyScriptable,
        QueryPropertyStored,
        QueryPropertyEditable,
        QueryPropertyUser,
        CreateInstance,
        IndexOfMethod,
        RegisterPropertyMetaType,
        RegisterMethodArgumentMetaType
    };

    int static_metacall(Call, int, void **) const;
    static int metacall(QObject *, Call, int, void **);

    struct { // private data
        const QMetaObject *superdata;
        const QByteArrayData *stringdata;
        const uint *data;
        typedef void (*StaticMetacallFunction)(QObject *, QMetaObject::Call, int, void **);
        StaticMetacallFunction static_metacall;
        const QMetaObject * const *relatedMetaObjects;
        void *extradata; //reserved for future use
    } d;
};

从接口命名就可以简单分析出可以获取类名、类信息、方法（细分为信号、槽、构造函数、一般函数）、属性、枚举等信息

枚举类型Call中实际给出了可以进行的操作，包括调用方法、读写属性、查询属性各种特性、创建实例、注册属性类型、注册方法参数类型

enum Call {
   InvokeMetaMethod,
   ReadProperty,
   WriteProperty,
   ResetProperty,
   QueryPropertyDesignable,
   QueryPropertyScriptable,
   QueryPropertyStored,
   QueryPropertyEditable,
   QueryPropertyUser,
   CreateInstance,
   IndexOfMethod,
   RegisterPropertyMetaType,
   RegisterMethodArgumentMetaType
};

还给出了activate（发射信号实际调用的函数），connect（连接信号与槽），disconnect（断连信号与槽）的接口

QMetaObject实现分析

获取超类QMetaObject 指针

inline const QMetaObject *QMetaObject::superClass() const
{ return d.superdata; }

获取类名
先看一个转换函数

static inline const QMetaObjectPrivate *priv(const uint* data)
{ return reinterpret_cast(data); }

这个函数将uint*指针转化为QMetaObjectPrivate ，也就是说QMetaObject中的d.data实际就是一个QMetaObjectPrivate 结构体指针

那么让我们看看QMetaObjectPrivate 这个结构体

struct QMetaObjectPrivate
{
    enum { OutputRevision = 7 }; // Used by moc, qmetaobjectbuilder and qdbus

    int revision;
    int className;
    int classInfoCount, classInfoData;
    int methodCount, methodData;
    int propertyCount, propertyData;
    int enumeratorCount, enumeratorData;
    int constructorCount, constructorData; //since revision 2
    int flags; //since revision 3
    int signalCount; //since revision 4 
    //...
}

原来这个结构体就是对应我们上节的qt_meta_data_MyClass整型数组，里面记录了类、方法、属性等名称字符串的索引、参数的类型信息等

那么再来看获取类名的步骤

const char *QMetaObject::className() const
{
    return objectClassName(this);
}

static inline const char *objectClassName(const QMetaObject *m)
{
    return rawStringData(m, priv(m->d.data)->className);
}

static inline const char *rawStringData(const QMetaObject *mo, int index)
{
    return stringData(mo, index).data();
}

static inline const QByteArray stringData(const QMetaObject *mo, int index)
{
    const QByteArrayDataPtr data = { const_cast(&mo->d.stringdata[index]) };
    return data;
}

实际就是通过d.data中记录的索引找到d.stringdata中的字符串，即mo->d.stringdata[index]

判断继承关系

bool QMetaObject::inherits(const QMetaObject *metaObject)
{
    const QMetaObject *m = this;
    do {
        if (metaObject == m)
            return true;
    } while ((m = m->d.superdata));
    return false;
}

就是循环比较超类的QMetaObject是否等于这个metaObject

方法偏移

int QMetaObject::methodOffset() const
{
    int offset = 0;
    const QMetaObject *m = d.superdata;
    while (m) {
        offset += priv(m->d.data)->methodCount;
        m = m->d.superdata;
    }
    return offset;
}

返回所有基类的方法数之和

方法总数

int QMetaObject::methodCount() const
{
    int n = priv(d.data)->methodCount;
    const QMetaObject *m = d.superdata;
    while (m) {
        n += priv(m->d.data)->methodCount;
        m = m->d.superdata;
    }
    return n;
}

返回自身和基类所有的方法数之和

方法索引

int QMetaObject::indexOfMethod(const char *method) const
{
    const QMetaObject *m = this;
    int i;
    QArgumentTypeArray types;
    QByteArray name = QMetaObjectPrivate::decodeMethodSignature(method, types);
    i = indexOfMethodRelative<0>(&m, name, types.size(), types.constData());
    if (i >= 0)
        i += m->methodOffset();
    return i;
}

说明下decodeMethodSignature用来解析一个函数字符串如func(int a, QMap b)，返回值是函数名func，types中记录参数类型

然后通过indexOfMethodRelative去匹配是否有函数名和参数个数，参数类型都一样的，有就返回索引，最后和方法偏移相加，就是该方法的最终索引

根据索引获取方法

QMetaMethod QMetaObject::method(int index) const
{
    int i = index;
    i -= methodOffset();
    if (i < 0 && d.superdata)
        return d.superdata->method(index);

    QMetaMethod result;
    if (i >= 0 && i < priv(d.data)->methodCount) {
        result.mobj = this;
        result.handle = priv(d.data)->methodData + 5*i;
    }
    return result;
}

返回的是一个QMetaMethod类，Qt提供了QMetaClassInfo，QMetaMethod、QMetaProperty、QMetaEnum来包装这些元信息和对其的一些操作，比如QMetaMethod就提供了name、parameterTypes、invoke等接口。

其它QMetaObejct中classinfo、property、enum的接口与上面method的接口实现类似。

继续探索QMetaOjbect中invokeMethod接口的实现

bool QMetaObject::invokeMethod(QObject *obj,
                               const char *member,
                               Qt::ConnectionType type,
                               QGenericReturnArgument ret,
                               QGenericArgument val0,
                               QGenericArgument val1,
                               QGenericArgument val2,
                               QGenericArgument val3,
                               QGenericArgument val4,
                               QGenericArgument val5,
                               QGenericArgument val6,
                               QGenericArgument val7,
                               QGenericArgument val8,
                               QGenericArgument val9)
{
    if (!obj)
        return false;

    QVarLengthArray 512> sig;
    int len = qstrlen(member);
    if (len <= 0)
        return false;
    sig.append(member, len);
    sig.append('(');

    const char *typeNames[] = {ret.name(), val0.name(), val1.name(), val2.name(), val3.name(),
                               val4.name(), val5.name(), val6.name(), val7.name(), val8.name(),
                               val9.name()};

    int paramCount;
    for (paramCount = 1; paramCount < MaximumParamCount; ++paramCount) {
        len = qstrlen(typeNames[paramCount]);
        if (len <= 0)
            break;
        sig.append(typeNames[paramCount], len);
        sig.append(',');
    }
    if (paramCount == 1)
        sig.append(')'); // no parameters
    else
        sig[sig.size() - 1] = ')';
    sig.append('\0');

    const QMetaObject *meta = obj->metaObject();
    int idx = meta->indexOfMethod(sig.constData());
    if (idx < 0) {
        QByteArray norm = QMetaObject::normalizedSignature(sig.constData());
        idx = meta->indexOfMethod(norm.constData());
    }

    if (idx < 0 || idx >= meta->methodCount()) {
        // This method doesn't belong to us; print out a nice warning with candidates.
        qWarning("QMetaObject::invokeMethod: No such method %s::%s%s",
                 meta->className(), sig.constData(), findMethodCandidates(meta, member).constData());
        return false;
    }
    QMetaMethod method = meta->method(idx);
    return method.invoke(obj, type, ret,
                         val0, val1, val2, val3, val4, val5, val6, val7, val8, val9);
}

嗯，就是根据函数名、函数返回类型、参数类型，构建函数签名sig，然后通过indexOfMethod获取索引号，再通过method得到QMetaMethod ，最后实际调用的是QMetaMethod 的invoke接口

bool QMetaMethod::invoke(QObject *object,
                         Qt::ConnectionType connectionType,
                         QGenericReturnArgument returnValue,
                         QGenericArgument val0,
                         QGenericArgument val1,
                         QGenericArgument val2,
                         QGenericArgument val3,
                         QGenericArgument val4,
                         QGenericArgument val5,
                         QGenericArgument val6,
                         QGenericArgument val7,
                         QGenericArgument val8,
                         QGenericArgument val9) const
{
    if (!object || !mobj)
        return false;

    Q_ASSERT(mobj->cast(object));

    // check return type
    if (returnValue.data()) {
        const char *retType = typeName();
        if (qstrcmp(returnValue.name(), retType) != 0) {
            // normalize the return value as well
            QByteArray normalized = QMetaObject::normalizedType(returnValue.name());
            if (qstrcmp(normalized.constData(), retType) != 0) {
                // String comparison failed, try compare the metatype.
                int t = returnType();
                if (t == QMetaType::UnknownType || t != QMetaType::type(normalized))
                    return false;
            }
        }
    }

    // check argument count (we don't allow invoking a method if given too few arguments)
    const char *typeNames[] = {
        returnValue.name(),
        val0.name(),
        val1.name(),
        val2.name(),
        val3.name(),
        val4.name(),
        val5.name(),
        val6.name(),
        val7.name(),
        val8.name(),
        val9.name()
    };
    int paramCount;
    for (paramCount = 1; paramCount < MaximumParamCount; ++paramCount) {
        if (qstrlen(typeNames[paramCount]) <= 0)
            break;
    }
    if (paramCount <= QMetaMethodPrivate::get(this)->parameterCount())
        return false;

    // check connection type
    QThread *currentThread = QThread::currentThread();
    QThread *objectThread = object->thread();
    if (connectionType == Qt::AutoConnection) {
        connectionType = currentThread == objectThread
                         ? Qt::DirectConnection
                         : Qt::QueuedConnection;
    }

#ifdef QT_NO_THREAD
    if (connectionType == Qt::BlockingQueuedConnection) {
        connectionType = Qt::DirectConnection;
    }
#endif

    // invoke!
    void *param[] = {
        returnValue.data(),
        val0.data(),
        val1.data(),
        val2.data(),
        val3.data(),
        val4.data(),
        val5.data(),
        val6.data(),
        val7.data(),
        val8.data(),
        val9.data()
    };
    int idx_relative = QMetaMethodPrivate::get(this)->ownMethodIndex();
    int idx_offset =  mobj->methodOffset();
    Q_ASSERT(QMetaObjectPrivate::get(mobj)->revision >= 6);
    QObjectPrivate::StaticMetaCallFunction callFunction = mobj->d.static_metacall;

    if (connectionType == Qt::DirectConnection) {
        if (callFunction) {
            callFunction(object, QMetaObject::InvokeMetaMethod, idx_relative, param);
            return true;
        } else {
            return QMetaObject::metacall(object, QMetaObject::InvokeMetaMethod, idx_relative + idx_offset, param) < 0;
        }
    } else if (connectionType == Qt::QueuedConnection) {
        if (returnValue.data()) {
            qWarning("QMetaMethod::invoke: Unable to invoke methods with return values in "
                     "queued connections");
            return false;
        }

        int nargs = 1; // include return type
        void **args = (void **) malloc(paramCount * sizeof(void *));
        Q_CHECK_PTR(args);
        int *types = (int *) malloc(paramCount * sizeof(int));
        Q_CHECK_PTR(types);
        types[0] = 0; // return type
        args[0] = 0;

        for (int i = 1; i < paramCount; ++i) {
            types[i] = QMetaType::type(typeNames[i]);
            if (types[i] != QMetaType::UnknownType) {
                args[i] = QMetaType::create(types[i], param[i]);
                ++nargs;
            } else if (param[i]) {
                // Try to register the type and try again before reporting an error.
                void *argv[] = { &types[i], &i };
                QMetaObject::metacall(object, QMetaObject::RegisterMethodArgumentMetaType,
                                      idx_relative + idx_offset, argv);
                if (types[i] == -1) {
                    qWarning("QMetaMethod::invoke: Unable to handle unregistered datatype '%s'",
                            typeNames[i]);
                    for (int x = 1; x < i; ++x) {
                        if (types[x] && args[x])
                            QMetaType::destroy(types[x], args[x]);
                    }
                    free(types);
                    free(args);
                    return false;
                }
            }
        }

        QCoreApplication::postEvent(object, new QMetaCallEvent(idx_offset, idx_relative, callFunction,
                                                        0, -1, nargs, types, args));
    } else { // blocking queued connection
#ifndef QT_NO_THREAD
        if (currentThread == objectThread) {
            qWarning("QMetaMethod::invoke: Dead lock detected in "
                        "BlockingQueuedConnection: Receiver is %s(%p)",
                        mobj->className(), object);
        }

        QSemaphore semaphore;
        QCoreApplication::postEvent(object, new QMetaCallEvent(idx_offset, idx_relative, callFunction,
                                                        0, -1, 0, 0, param, &semaphore));
        semaphore.acquire();
#endif // QT_NO_THREAD
    }
    return true;
}

代码首先检查返回值的类型是否正确；
再检查参数的个数是否匹配；
再依据当前线程和被调对象所属 线程来调整connnection type；
如果是Qt::DirectConnection，直接调用

QMetaObject::metacall(object, QMetaObject::InvokeMetaMethod, methodIndex, param)

如果是Qt::QueuedConnection，即异步调用

QCoreApplication::postEvent(object, new QMetaCallEvent(idx_offset, idx_relative, callFunction,0, -1, nargs, types, args));

当然还有一种Qt::BlockingQueuedConnection阻塞式异步调用，通过QSemaphore信号量来等待调用结束后再继续执行

QSemaphore semaphore;
QCoreApplication::postEvent(object, new QMetaCallEvent(idx_offset, idx_relative, callFunction, 0, -1, 0, 0, param, &semaphore));
semaphore.acquire();

关于异步调用，是在对象所属线程中的事件循环中，从事件队列中取得这个事件时，再去调用这个函数

int QMetaObject::metacall(QObject *object, Call cl, int idx, void **argv)
{
    if (object->d_ptr->metaObject)
        return object->d_ptr->metaObject->metaCall(object, cl, idx, argv);
    else
        return object->qt_metacall(cl, idx, argv);
}

如果是QObject类，那就直接调用metaCall，否则就是QObject的派生类，调用qt_metacall，就是moc文件自动生成的代码了。

moc_myclass.cpp参考上一章，下面回顾下qt_metacall的代码加深理解

int MyClass::qt_metacall(QMetaObject::Call _c, int _id, void **_a)
{
    _id = QObject::qt_metacall(_c, _id, _a);
    if (_id < 0)
        return _id;
    if (_c == QMetaObject::InvokeMetaMethod) {
        if (_id < 3)
            qt_static_metacall(this, _c, _id, _a);
        _id -= 3;
    } else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
        if (_id < 3)
            *reinterpret_cast<int*>(_a[0]) = -1;
        _id -= 3;
    }
#ifndef QT_NO_PROPERTIES
   else if (_c == QMetaObject::ReadProperty || _c == QMetaObject::WriteProperty
            || _c == QMetaObject::ResetProperty || _c == QMetaObject::RegisterPropertyMetaType) {
        qt_static_metacall(this, _c, _id, _a);
        _id -= 1;
    } else if (_c == QMetaObject::QueryPropertyDesignable) {
        _id -= 1;
    } else if (_c == QMetaObject::QueryPropertyScriptable) {
        _id -= 1;
    } else if (_c == QMetaObject::QueryPropertyStored) {
        _id -= 1;
    } else if (_c == QMetaObject::QueryPropertyEditable) {
        _id -= 1;
    } else if (_c == QMetaObject::QueryPropertyUser) {
        _id -= 1;
    }
#endif // QT_NO_PROPERTIES
    return _id;
}

可以看到如果是QMetaObject::InvokeMetaMethod，那么将调用

qt_static_metacall(this, _c, _id, _a);

void MyClass::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
{
    if (_c == QMetaObject::CreateInstance) {
        switch (_id) {
        case 0: { MyClass *_r = new MyClass((*reinterpret_cast< int(*)>(_a[1])),(*reinterpret_cast< QObject*(*)>(_a[2])));
            if (_a[0]) *reinterpret_cast(_a[0]) = _r; } break;
        default: break;
        }
    } else if (_c == QMetaObject::InvokeMetaMethod) {
        MyClass *_t = static_cast(_o);
        Q_UNUSED(_t)
        switch (_id) {
        case 0: _t->signal1((*reinterpret_cast< int(*)>(_a[1]))); break;
        case 1: { int _r = _t->slot1((*reinterpret_cast< int(*)>(_a[1])));
            if (_a[0]) *reinterpret_cast< int*>(_a[0]) = _r; }  break;
        case 2: { int _r = _t->method1((*reinterpret_cast< int(*)>(_a[1])));
            if (_a[0]) *reinterpret_cast< int*>(_a[0]) = _r; }  break;
        default: ;
        }
    } else if (_c == QMetaObject::IndexOfMethod) {
        int *result = reinterpret_cast<int *>(_a[0]);
        void **func = reinterpret_cast<void **>(_a[1]);
        {
            typedef void (MyClass::*_t)(int );
            if (*reinterpret_cast<_t *>(func) == static_cast<_t>(&MyClass::signal1)) {
                *result = 0;
                return;
            }
        }
    }
#ifndef QT_NO_PROPERTIES
    else if (_c == QMetaObject::ReadProperty) {
    } else if (_c == QMetaObject::WriteProperty) {
    } else if (_c == QMetaObject::ResetProperty) {
    }
#endif // QT_NO_PROPERTIES
}

这段代码将调用最终转到我们自己的实现的函数（这里是signal1、slot1、method1）中来。这个函数不仅提供了method的动态调用，而且也提供了property的动态操作方法。可想而知，property的动态调用的实现方式一定和invocalbe method是类似的。

总结

通过上一节moc文件分析，和这一节的QMetaObject源码分析，我们应该是对Qt Meta-Object Model有了一个清楚的认识

• Qt提供了一个QObject的基类
• Qt扩展了C++语法，提供了Q_OBJECT、Q_INVOKABLE、signals、slots、emit、SIGNAL，SLOT、Q_PROPERT、Q_ENUM、Q_FLAG、Q_CLASSINFO等宏，moc会识别这些宏并生成对应的moc源代码
• Q_OBJECT宏中声明了QMetaObject的静态对象，QMetaObject中记录了classiofo、method、property、enum，并提供了metacall来操作

*关于信号与槽机制关键几个接口activate和connect、disconect的实现，见下一节