省去大部分virtual和public方法后，Qobject主要剩下以下成员：
//qobject.h
class Q_CORE_EXPORT Qobject{
Q_OBJECT
Q_PROPERTY(QString objectName READ objectName WRITE setObjectName NOTIFY objectNameChanged)
Q_DECLARE_PRIVATE(QObject)
public:
Q_INVOKABLE explicit QObject(QObject *parent=nullptr);
virtual ~QObject();
//...
protected:
QObject(QObjectPrivate &dd, QObject *parent = nullptr);
//...
protected:
QScopedPointer<QObjectData> d_ptr;
static const QMetaObject staticQtMetaObject;
//...
private:
Q_DISABLE_COPY(QObject)
//...
}一、Q_OBJECT
#define Q_OBJECT \
public: \
QT_WARNING_PUSH \
Q_OBJECT_NO_OVERRIDE_WARNING \
static const QMetaObject staticMetaObject; \
virtual const QMetaObject *metaObject() const; \
virtual void *qt_metacast(const char *); \
virtual int qt_metacall(QMetaObject::Call, int, void **); \
QT_TR_FUNCTIONS \
private: \
Q_OBJECT_NO_ATTRIBUTES_WARNING \
Q_DECL_HIDDEN_STATIC_METACALL static void qt_static_metacall(QObject *, QMetaObject::Call, int, void **); \
QT_WARNING_POP \
struct QPrivateSignal {}; \
QT_ANNOTATE_CLASS(qt_qobject, "")
1、宏 QT_WARNING_PUSH 和 QT_WARNING_POP用于保存和恢复编译器的警告状态，以便在宏定义内部做一些修改或设置，而不影响用户定义的警告状态。
2、Q_OBJECT_NO_OVERRIDE_WARNING和Q_OBJECT_NO_ATTRIBUTES_WARNING这两个宏用于控制是否发出关于未覆盖（override）的警告或者关于某些属性的警告。
3、QT_TR_FUNCTIONS这个宏用于启用Qt的国际化（internationalization）功能，使得文本可以被翻译为不同的语言。
4、Q_DECL_HIDDEN_STATIC_METACALL在qobjectdefs.h有定义：
# define Q_DECL_HIDDEN_STATIC_METACALL Q_DECL_HIDDEN
使用 Q_DECL_HIDDEN 可以将类或函数标记为在外部接口中隐藏的，从而使它们对库的用户不可见。这对于避免一些链接时的符号冲突和提高库的封装性很有帮助。这个宏可能会被翻译成 __attribute__((visibility("hidden")))。也就是说qt_static_metacall这个函数没用到，我们忽略。去除和编译器相关的宏，Q_OBJECT剩下的关键部分：
//qobjectdefs.h
#define Q_OBJECT \
public: \
static const QMetaObject staticMetaObject; \
virtual const QMetaObject *metaObject() const; \
virtual void *qt_metacast(const char *); \
virtual int qt_metacall(QMetaObject::Call, int, void **); \
private: \
Q_DECL_HIDDEN_STATIC_METACALL static void qt_static_metacall(QObject *, QMetaObject::Call, int, void **);
Q_OBJECT宏声明了1个QMetaObject变量和3个QMetaObject相关的虚函数。QMetaObject类非常重要，和元对象系统相关。二、Q_PROPERTY
//qobjectdefs.h
#define Q_PROPERTY(...) QT_ANNOTATE_CLASS(qt_property, __VA_ARGS__)
#define QT_ANNOTATE_CLASS(type, ...)
在 qobjectdefs.h 中我们并没有看到 Q_PROPERTY 的准确定义。很多Qt的宏和特殊功能是通过moc生成的代码而不是在头文件中显式定义的。C++编译器能够识别 Q_PROPERTY 宏，是因为moc编译时生成了相应的代码。
使用Q_PROPERTY后，相当于把属性纳入了元对象系统，而且给出了一段Q_PROPERTY更细致的声明：
Q_PROPERTY(type name
(READ getFunction [WRITE setFunction] |
MEMBER memberName [(READ getFunction | WRITE setFunction)])
[RESET resetFunction]
[NOTIFY notifySignal]
[REVISION int | REVISION(int[, int])]
[DESIGNABLE bool]
[SCRIPTABLE bool]
[STORED bool]
[USER bool]
[BINDABLE bindableProperty]
[CONSTANT]
[FINAL]
[REQUIRED])
三、Q_DECLARE_PRIVATE
//qglobal.h
#define Q_DECLARE_PRIVATE(Class) \
inline Class##Private* d_func() \
{ Q_CAST_IGNORE_ALIGN(return reinterpret_cast<Class##Private *>(qGetPtrHelper(d_ptr));) } \
inline const Class##Private* d_func() const \
{ Q_CAST_IGNORE_ALIGN(return reinterpret_cast<const Class##Private *>(qGetPtrHelper(d_ptr));) } \
friend class Class##Private;
加入参数并翻译过后：
inline QObjectPrivate* d_func()
{ Q_CAST_IGNORE_ALIGN(return reinterpret_cast<QObjectPrivate *>(qGetPtrHelper(d_ptr));) }
inline const QObjectPrivate* d_func() const
{ Q_CAST_IGNORE_ALIGN(return reinterpret_cast<const QObjectPrivate *>(qGetPtrHelper(d_ptr));) }
friend class QObjectPrivate;
qGetPtrHelper()方法的定义：
//qglobal.h
template <typename T> static inline T *qGetPtrHelper(T *ptr) { return ptr; }
template <typename Wrapper> static inline typename Wrapper::pointer qGetPtrHelper(const Wrapper &p) { return p.data(); }
qGetPtrHelper是一个模板函数，其目的是为了获取指针或类似指针的数据。
Q_CAST_IGNORE_ALIGN用于禁用GCC编译器的 -Wcast-align 警告。
Q_DECLARE_PRIVATE宏定义了2个函数和1个友元类。2个d_func只是签名不同，传入参数d_ptr，都返回一个QObjectPrivate*类型的指针，而且友元类的名称也是QObjectPrivate。四、QObjectData和QObjectPrivate
关于变量QScopedPointer<QObjectData> d_ptr:
QScopedPointer类是用于存储指向动态分配对象的指针，并在其销毁时删除它，确保指向的对象在当前作用域消失时将被删除。
所以QScopedPointer<QObjectData>是一个QObjectData的指针。
QObjectData定义：
//qobject.h
class Q_CORE_EXPORT QObjectData {
//防止对象拷贝
Q_DISABLE_COPY(QObjectData)
public:
QObjectData() = default;
virtual ~QObjectData() = 0;
QObject *q_ptr;
QObject *parent;
QObjectList children;
uint isWidget : 1;
uint blockSig : 1;
uint wasDeleted : 1;
uint isDeletingChildren : 1;
uint sendChildEvents : 1;
uint receiveChildEvents : 1;
uint isWindow : 1; //for QWindow
uint deleteLaterCalled : 1;
uint unused : 24;
int postedEvents;
QDynamicMetaObjectData *metaObject;
QMetaObject *dynamicMetaObject() const;
#ifdef QT_DEBUG
enum { CheckForParentChildLoopsWarnDepth = 4096 };
#endif
};
上面说到d_func函数传入参数d_ptr，返回的QObjectPrivate*类型的指针，而d_ptr是QObjectData，那也就是说QObjectPrivate是QObjectData的子类。我们且看QObjectPrivate的定义:
//qobject_p.h
class Q_CORE_EXPORT QObjectPrivate : public QObjectData
{
Q_DECLARE_PUBLIC(QObject)
public:
struct ExtraData{
//...
}；
//和信号&槽相关
struct ConnectionOrSignalVector{
//...
}；
//和信号&槽相关
struct Connection : public ConnectionOrSignalVector{
//...
};
//和信号&槽相关
struct Sender{
//...
};
//和信号&槽相关
struct ConnectionData{
//...
};
QObjectPrivate(int version = QObjectPrivateVersion);
virtual ~QObjectPrivate();
public:
ExtraData *extraData;
QAtomicPointer<QThreadData> threadData;
using ConnectionDataPointer = QExplicitlySharedDataPointer<ConnectionData>;
QAtomicPointer<ConnectionData> connections;
union {
QObject *currentChildBeingDeleted;
QAbstractDeclarativeData *declarativeData;
};
QAtomicPointer<QtSharedPointer::ExternalRefCountData> sharedRefcount;
}
Q_DECLARE_PUBLIC(QObject)定义：
//qglobal.h
#define Q_DECLARE_PUBLIC(Class) \
inline Class* q_func() { return static_cast<Class *>(q_ptr); } \
inline const Class* q_func() const { return static_cast<const Class *>(q_ptr); } \
friend class Class;
翻译过后：
inline QObject* q_func() { return static_cast<QObject *>(q_ptr); }
inline const QObject* q_func() const { return static_cast<const QObject *>(q_ptr); } \
friend class QObject;
这个宏实际上定义了2个签名不一样的函数q_func()，返回q_ptr指针，声明了QObject是友元类。
QObjectPrivate的构造器定义如下：
//qobject.cpp
QObjectPrivate::QObjectPrivate(int version)
: threadData(nullptr), currentChildBeingDeleted(nullptr)
{
checkForIncompatibleLibraryVersion(version);
// QObjectData initialization
q_ptr = nullptr;
parent = nullptr; // no parent yet. It is set by setParent()
isWidget = false; // assume not a widget object
blockSig = false; // not blocking signals
wasDeleted = false; // double-delete catcher
isDeletingChildren = false; // set by deleteChildren()
sendChildEvents = true; // if we should send ChildAdded and ChildRemoved events to parent
receiveChildEvents = true;
postedEvents = 0;
extraData = nullptr;
metaObject = nullptr;
isWindow = false;
deleteLaterCalled = false;
}
基本上是对继承下来的变量和自身变量进行初始化。五、QObject()
当实例化一个继承自QObject的对象时，首先会调用QObject的构造器，构造器开始构造对象模型的世界，我们且看QObject构造函数QObject()的定义：
//qobject.cpp
QObject::QObject(QObject *parent)
: QObject(*new QObjectPrivate, parent)
{
}
//qobject.cpp
QObject::QObject(QObjectPrivate &dd, QObject *parent)
: d_ptr(&dd)
{
Q_ASSERT_X(this != parent, Q_FUNC_INFO, "Cannot parent a QObject to itself");
Q_D(QObject);
d_ptr->q_ptr = this;
auto threadData = (parent && !parent->thread()) ? parent->d_func()->threadData.loadRelaxed() : QThreadData::current();
threadData->ref();
d->threadData.storeRelaxed(
threadData);
if (parent) {
QT_TRY {
if (!check_parent_thread(parent, parent ? parent->d_func()->threadData.loadRelaxed() : nullptr,
threadData))
parent = nullptr;
if (d->isWidget) {
if (parent) {
d->parent = parent;
d->parent->d_func()->children.append(
this);
}
// no events sent here, this is done at the end of the QWidget constructor
} else {
setParent(parent);
}
} QT_CATCH(...) {
threadData->deref();
QT_RETHROW;
}
}
#if QT_VERSION < 0x60000
qt_addObject(this);
#endif
if (Q_UNLIKELY(qtHookData[QHooks::AddQObject]))
reinterpret_cast<QHooks::AddQObjectCallback>(qtHookData[QHooks::AddQObject])(this);
Q_TRACE(QObject_ctor, this);
}
public的构造函数实际上是调用了protected的构造函数。
默认新建了一个QObjectPrivate并作为构造函数参数传入，赋值给了d_ptr。变量QScopedPointer<QObjectData> d_ptr在构造函数里实际被赋值为其新建的子实例QObjectPrivate。
Q_D(QObject)定义：
//qglobal.h
#define Q_D(Class) Class##Private * const d = d_func()
调用d_func()得到QObjectPrivate* 并赋值给d，此时d和d_ptr都指向前面实例化的QObjectPrivate。
d_ptr->q_ptr = this;
将QObjectPrivate->q_ptr设置为自身。
//qobject.cpp
auto threadData = (parent && !parent->thread()) ? parent->d_func()->threadData.loadRelaxed() : QThreadData::current();
threadData->ref();
d->threadData.storeRelaxed(
threadData);
检查 parent 是否非空且它所属的线程是否为空，如果都不空的话，获取parent的线程数据；否则获取当前的线程数据。将线程数据存储到对象内部的数据结构中。
//qobject.cpp
if (!check_parent_thread(parent, parent ? parent->d_func()->threadData.loadRelaxed() : nullptr, threadData))
parent = nullptr;
检查parent和当前对象是否在相同的线程中，如果不在相同线程中，将 parent 设置为 nullptr。
//qobject.cpp
if (d->isWidget) {
if (parent) {
d->parent = parent;
d->parent->d_func()->children.append(this);
}
}else{
//...
}
如果对象是一个QWidget，parent不空，则建立起对象和parent的联系，对象的父对象就是parent，parent的children添加该对象。
//qobject.cpp
if (d->isWidget) {
//...
} else {
setParent(parent);
}
如果对象不是QWidget，通过setParent(parent)设置父对象。
setParent()的定义：
//qobject.cpp
void QObject::setParent(QObject *parent)
{
Q_D(QObject);
Q_ASSERT(!d->isWidget);
d->setParent_helper(parent);
}
继续调用d->setParent_helper(parent)。
setParent_helper()的定义：
void QObjectPrivate::setParent_helper(QObject *o)
{
Q_Q(QObject);
Q_ASSERT_X(q != o, Q_FUNC_INFO, "Cannot parent a QObject to itself");
#ifdef QT_DEBUG
const auto checkForParentChildLoops = qScopeGuard(
[&](){
int depth = 0;
auto p = parent;
while (p) {
if (++depth == CheckForParentChildLoopsWarnDepth) {
qWarning(
"QObject %p (class: '%s', object name: '%s') may have a loop in its parent-child chain; "
"this is undefined behavior",
q, q->metaObject()->className(), qPrintable(q->objectName()));
}
p = p->parent();
}
});
#endif
if (o == parent)
return;
if (parent) {
QObjectPrivate *parentD = parent->d_func();
if (parentD->isDeletingChildren && wasDeleted
&& parentD->currentChildBeingDeleted == q) {
// don't do anything since QObjectPrivate::deleteChildren() already
// cleared our entry in parentD->children.
} else {
const int index = parentD->children.indexOf(q);
if (index < 0) {
// we're probably recursing into setParent() from a ChildRemoved event, don't do anything
} else if (parentD->isDeletingChildren) {
parentD->children[index] = 0;
} else {
parentD->children.removeAt(index);
if (sendChildEvents && parentD->receiveChildEvents) {
QChildEvent e(QEvent::ChildRemoved, q);
QCoreApplication::sendEvent(parent, &e);
}
}
}
}
parent = o;
if (parent) {
// object hierarchies are constrained to a single thread
if (threadData != parent->d_func()->threadData) {
qWarning(
"QObject::setParent: Cannot set parent, new parent is in a different thread");
parent = nullptr;
return;
}
parent->d_func()->children.append(q);
if(sendChildEvents && parent->d_func()->receiveChildEvents) {
if (!isWidget) {
QChildEvent e(QEvent::ChildAdded, q);
QCoreApplication::sendEvent(parent, &e);
}
}
}
if (!wasDeleted && !isDeletingChildren && declarativeData && QAbstractDeclarativeData::parentChanged)
QAbstractDeclarativeData::parentChanged(declarativeData, q, o);
}
Q_Q(QObject)的定义：
//qglobal.h
#define Q_Q(Class) Class * const q = q_func()
通过q_func()获取QObjectPrivate的q_ptr，在上面我们知道q_ptr指向了QObject，所以q和q_ptr都指向QObject。
#ifdef QT_DEBUG
const auto checkForParentChildLoops = qScopeGuard(
[&](){
int depth = 0;
auto p = parent;
while (p) {
if (++depth == CheckForParentChildLoopsWarnDepth) {
qWarning(
"QObject %p (class: '%s', object name: '%s') may have a loop in its parent-child chain; "
"this is undefined behavior",
q, q->metaObject()->className(), qPrintable(q->objectName()));
}
p = p->parent();
}
});
#endif
这一段通过warning可以推断出是在检测父子关系链中是否存在循环，如果循环链深度超过阈值，则警告。
if (o == parent)
return;
如果已经设置过parent且没变，直接返回。
//如果已经有parent
if (parent) {
//获取父对象的QObjectPrivate
QObjectPrivate *parentD = parent->d_func();
//检查父对象是否正在删除其子对象，当前对象是否已经被删除，前对象是否是父对象正在删除的子对象。
//如果这些条件都成立，就跳过后续的处理，因为在删除子对象的过程中已经做了清理工作。
if (parentD->isDeletingChildren && wasDeleted
&& parentD->currentChildBeingDeleted == q) {
// don't do anything since QObjectPrivate::deleteChildren() already
// cleared our entry in parentD->children.
} else {
//获取当前对象在其父对象的子对象列表中的索引
const int index = parentD->children.indexOf(q);
//如果索引为负数，可能表示正在从 ChildRemoved 事件中递归到 setParent()，这时不执行任何操作。
if (index < 0) {
// we're probably recursing into setParent() from a ChildRemoved event, don't do anything
} else if (parentD->isDeletingChildren) {//如果父对象正在删除其子对象，将相应的子对象指针更新为0。
parentD->children[index] = 0;
} else {//否则，从父对象的子对象列表中移除当前对象
parentD->children.removeAt(
index);
//发送一个 ChildRemoved 事件给父对象。
if (sendChildEvents && parentD->receiveChildEvents) {
QChildEvent e(QEvent::ChildRemoved, q);
QCoreApplication::sendEvent(parent,
&e);
}
}
}
}
上面这一段是在已有perent的情况下，断开parent和当前对象的联系，并确保在移除子对象时做了适当的清理和事件通知。实际上是为下面刷新parent做准备。
parent = o;//更新parent
//parent赋值后
if (parent) {
// object hierarchies are constrained to a single thread
// 对象层次结构受限于单个线程
// 比较当前对象的线程数据和父对象的线程数据，如果它们不一致
if (threadData != parent->d_func()->threadData) {
qWarning(
"QObject::setParent: Cannot set parent, new parent is in a different thread");
//父对象置空
parent = nullptr;
//直接返回
return;
}
//将当前对象添加到父对象的子对象列表中。
parent->d_func()->children.append(
q);
if(sendChildEvents && parent->d_func()->receiveChildEvents) {
if (!isWidget) {
//将这个事件发送给父对象
QChildEvent e(QEvent::ChildAdded, q);
QCoreApplication::sendEvent(parent,
&e);
}
}
}
上面这一段是在设置对象的父对象后进行一些检查，确保父对象线程数据和该对象的一致，否则将parent设为nullptr，随后发送相应的ChildAdded事件给parent。
setParent_helper函数主要做了两件事:
1）确保旧parent安全撤离。
2）确保新parent正确设置。
简单概括一下构造函数QObject()的内容：
1）新建QObjectPrivate并赋值给d_ptr。
2）赋值d_ptr->q_ptr为对象本身。
3）初始化threadData。
4）检查当前对象和parent是否在同一线程.
5）为当前对象和parent设置关联.六、Q_DISABLE_COPY()
//qglobal.h
#define Q_DISABLE_COPY(Class) \
Class(const Class &) = delete;\
Class &operator=(const Class &) = delete;
这里删除了拷贝构造函数和拷贝赋值操作符，确保QObject不能被拷贝构造或赋值。觉得有帮助的话，打赏一下呗。。
