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Q_OBJECT

所有QObject的派生類在官方文檔中都推薦在頭文件中放置宏Q_OBJECT，那么該宏到底為我們做了哪些工作？在qobjectdef.h中有下面的代碼：

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#define Q_OBJECT \
public: \
Q_OBJECT_CHECK \
static const QMetaObject staticMetaObject; \
Q_OBJECT_GETSTATICMETAOBJECT \
virtual const QMetaObject *metaObject() const; \
virtual void *qt_metacast(const char *); \
QT_TR_FUNCTIONS \
virtual int qt_metacall(QMetaObject::Call, int, void **); \
private:

首先定義了一個Q_OBJECT_CHECK宏，這個宏在Q_OBJECT宏的上方定義：

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#define Q_OBJECT_CHECK \
template <typename T> inline void qt_check_for_QOBJECT_macro(const T &_q_argument) const \
{ int i = qYouForgotTheQ_OBJECT_Macro(this, &_q_argument); i = i; }

Q_OBJECT_CHECK實現了一個模板函數，該函數調用了qYouForgotTheQ_OBJECT_Macro的函數，qYouForgotTheQ_OBJECT_Macro在宏Q_OBJECT_CHECK下面有定義：

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template <typename T>
inline int qYouForgotTheQ_OBJECT_Macro(T, T) { return 0; }
template <typename T1, typename T2>
inline void qYouForgotTheQ_OBJECT_Macro(T1, T2) {}

從返回值情況上可以看到，調用的是有int返回值的那個模板函數。但是很不明白，為什么之后還要添加一句 i=i?，刨根之后，發現Q_OBJECT_CHECK宏并沒有做什么工作。

然后Q_OBJECT又幫我們定義了一個靜態的元對象，

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static const QMetaObject staticMetaObject; \
Q_OBJECT_GETSTATICMETAOBJECT \

Q_OBJECT_GETSTATICMETAOBJECT宏從名字上看就是為了獲取這個元對象，確實在定義了Q_NO_DATA_RELOCATION宏的情況下，Q_OBJECT_GETSTATICMETAOBJECT宏就為我們定義了獲取靜態元對象的方法。

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#ifdef Q_NO_DATA_RELOCATION
#define Q_OBJECT_GETSTATICMETAOBJECT static const QMetaObject &getStaticMetaObject();
#else
#define Q_OBJECT_GETSTATICMETAOBJECT
#endif

之后Q_OBJECT宏又給我們定義了連個虛函數用來獲取元對象指針和設置源對象。

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virtual const QMetaObject *metaObject() const; \
virtual void *qt_metacast(const char *); \

而定義的 QT_TR_FUNCTIONS 則表示是否支持I18N。

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#ifndef QT_NO_TRANSLATION
# ifndef QT_NO_TEXTCODEC
// full set of tr functions
// ### Qt 5: merge overloads
# define QT_TR_FUNCTIONS \
static inline QString tr(const char *s, const char *c = 0) \
{ return staticMetaObject.tr(s, c); } \
static inline QString trUtf8(const char *s, const char *c = 0) \
{ return staticMetaObject.trUtf8(s, c); } \
static inline QString tr(const char *s, const char *c, int n) \
{ return staticMetaObject.tr(s, c, n); } \
static inline QString trUtf8(const char *s, const char *c, int n) \
{ return staticMetaObject.trUtf8(s, c, n); }
# else
// no QTextCodec, no utf8
// ### Qt 5: merge overloads
# define QT_TR_FUNCTIONS \
static inline QString tr(const char *s, const char *c = 0) \
{ return staticMetaObject.tr(s, c); } \
static inline QString tr(const char *s, const char *c, int n) \
{ return staticMetaObject.tr(s, c, n); }
# endif
#else
// inherit the ones from QObject
# define QT_TR_FUNCTIONS
#endif

只要有所實現，tr的方法就通過靜態對象staticMetaObject的tr方法來實現。最后Q_OBJECT又定義了一個虛函數

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virtual int qt_metacall(QMetaObject::Call, int, void **);

看名字定義，應該是用來對元對象的調用。

合起來看所有的Q_OBJECT定義，都是為了操作元對象，并沒有所謂的信號和槽，屬性等內容，很顯然，QObject對象能夠支持這些功能，必然是通過QMetaObject這個元對象來實現的。盡管QMetaObject對象的實現有些龐大，但這個是所有的QOBject中最核心的一個實現，因此需要仔細分析該對象的每個定義：

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struct Q_CORE_EXPORT QMetaObject
{
const char *className() const; // 類名
const QMetaObject *superClass() const; // 父類的元對象
QObject *cast(QObject *obj) const; // 強制一個對象
#ifndef QT_NO_TRANSLATION
// ### Qt 4: Merge overloads
QString tr(const char *s, const char *c) const; // 翻譯函數
QString trUtf8(const char *s, const char *c) const;
QString tr(const char *s, const char *c, int n) const;
QString trUtf8(const char *s, const char *c, int n) const;
#endif // QT_NO_TRANSLATION
int methodOffset() const; // 方法偏移量
int enumeratorOffset() const; // 枚舉偏移量
int propertyOffset() const; // 屬性偏移量
int classInfoOffset() const; // 類信息數目
int constructorCount() const; // 構造函數數目
int methodCount() const; // 方法數目
int enumeratorCount() const; // 枚舉數據
int propertyCount() const; // 屬性數目
int classInfoCount() const; // 類信息數目
int indexOfConstructor(const char *constructor) const; // 構函函數索引
int indexOfMethod(const char *method) const; // 方法索引
int indexOfSignal(const char *signal) const; // 信號量索引
int indexOfSlot(const char *slot) const; // 槽索引
int indexOfEnumerator(const char *name) const; // 枚舉索引
int indexOfProperty(const char *name) const; // 屬性索引
int indexOfClassInfo(const char *name) const; // 類信息索引
QMetaMethod constructor(int index) const; // 構造方法
QMetaMethod method(int index) const; // 方法
QMetaEnum enumerator(int index) const; // 枚舉
QMetaProperty property(int index) const; // 屬性
QMetaClassInfo classInfo(int index) const; // 類屬性信息
QMetaProperty userProperty() const; // 用戶屬性
///////////////////////////////////////////////////////////////////////////////////////////////////////////////
static bool checkConnectArgs(const char *signal, const char *method);
static QByteArray normalizedSignature(const char *method);
static QByteArray normalizedType(const char *type);
// internal index-based connect
static bool connect(const QObject *sender, int signal_index,
const QObject *receiver, int method_index,
int type = 0, int *types = 0);
// 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); //obsolete
static void activate(QObject *sender, int from_signal_index, int to_signal_index, void **argv); //obsolete
static void activate(QObject *sender, const QMetaObject *, int local_signal_index, void **argv);
static void activate(QObject *sender, const QMetaObject *, int from_local_signal_index, int to_local_signal_index, void **argv); //obsolete
// internal guarded pointers
static void addGuard(QObject **ptr);
static void removeGuard(QObject **ptr);
static void changeGuard(QObject **ptr, QObject *o);
static bool invokeMethod(QObject *obj, const char *member,
Qt::ConnectionType,
QGenericReturnArgument ret,
QGenericArgument val0 = QGenericArgument(0),
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(0),
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(0),
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(0),
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(0),
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
};
int static_metacall(Call, int, void **) const;
static int metacall(QObject *, Call, int, void **);
#ifdef QT3_SUPPORT
QT3_SUPPORT const char *superClassName() const;
#endif
struct { // private data
const QMetaObject *superdata; // 父類
const char *stringdata; // 類名
const uint *data; // 任意指向數據的指針
const void *extradata; // 擴展數據
} d;
};

QMetaObject就內部一個結構體對象，包含了四個部分，分別是父類對象，自己元對象的名稱，以及一個指針任意值的指針數據和擴展數據，一般情況下，d.data表示的是QMetaObjectPrivate對象指針，在priv函數中可以找到一些痕跡：

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

按照Qt的實現慣例，使用Private對象做一些具體的工作，于是就有了QMetaObjectPrivate和QObjectPrivate

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struct QMetaObjectPrivate // 注意是一個結構體
{
int revision; // 版本
int className; // 類名，注意類型
int classInfoCount, classInfoData; // 類信息數據和數量
int methodCount, methodData; // 方法數據和數量
int propertyCount, propertyData; // 屬性數據和數量
int enumeratorCount, enumeratorData; // 枚舉數據和數量
int constructorCount, constructorData; //since revision 2 // 構造函數數據和數量
int flags; //since revision 3 // 標記
int signalCount; //since revision 4 // 信號量數目
// revision 5 introduces changes in normalized signatures, no new members
// 從元數據中獲取QMetaObjectPrivate對象指針，從data中得到！！
static inline const QMetaObjectPrivate *get(const QMetaObject *metaobject)
{ return reinterpret_cast<const QMetaObjectPrivate*>(metaobject->d.data); }
static int indexOfSignalRelative(const QMetaObject **baseObject,
const char* name,
bool normalizeStringData);
static int indexOfSlot(const QMetaObject *m,
const char *slot,
bool normalizeStringData);
static int originalClone(const QMetaObject *obj, int local_method_index);
#ifndef QT_NO_QOBJECT
//defined in qobject.cpp
enum DisconnectType { DisconnectAll, DisconnectOne };
static bool connect(const QObject *sender, int signal_index,
const QObject *receiver, int method_index,
int type = 0, int *types = 0);
static bool disconnect(const QObject *sender, int signal_index,
const QObject *receiver, int method_index,
DisconnectType = DisconnectAll);
static inline bool disconnectHelper(QObjectPrivate::Connection *c,
const QObject *receiver, int method_index,
QMutex *senderMutex, DisconnectType);
#endif
};

==================================================================

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class Q_CORE_EXPORT QObjectPrivate : public QObjectData
{
Q_DECLARE_PUBLIC(QObject)
public:
struct ExtraData // 定義額外數據
{
ExtraData() {}
#ifndef QT_NO_USERDATA
QVector<QObjectUserData *> userData;
#endif
QList<QByteArray> propertyNames; // 屬性名列表
QList<QVariant> propertyValues; // 屬性值
};
struct Connection // 定義連接信息
{
QObject *sender; // 發送者
QObject *receiver; // 接受者
int method; // 方法
uint connectionType : 3; // 0 == auto, 1 == direct, 2 == queued, 4 == blocking
QBasicAtomicPointer<int> argumentTypes; // 參數類型
// The next pointer for the singly-linked ConnectionList
Connection *nextConnectionList; // 下一個連接對象列表
//senders linked list
Connection *next; // 下一個連接
Connection **prev; // 上一個連接
~Connection();
};
// ConnectionList is a singly-linked list
struct ConnectionList { // 定義連接列表
ConnectionList() : first(0), last(0) {}
Connection *first; // 連接首
Connection *last; // 連接尾
};
struct Sender // 定義發送者
{
QObject *sender; // 發送者
int signal; // 信號
int ref; // 引用計數
};
QObjectPrivate(int version = QObjectPrivateVersion);
virtual ~QObjectPrivate();
void deleteChildren(); // 刪除所有子節點
void setParent_helper(QObject *); // 設置父節點
void moveToThread_helper(); // 轉到某個線程中
void setThreadData_helper(QThreadData *currentData, QThreadData *targetData); // 設置線程數據
void _q_reregisterTimers(void *pointer); // 設置注冊時間
bool isSender(const QObject *receiver, const char *signal) const; // 判斷信號量是否為發送者
QObjectList receiverList(const char *signal) const; // 接受信號的對象列表
QObjectList senderList() const; // 發出信息列表
void addConnection(int signal, Connection *c); // 添加一個信號連接
void cleanConnectionLists(); // 清理連接列表
#ifdef QT3_SUPPORT
void sendPendingChildInsertedEvents();
void removePendingChildInsertedEvents(QObject *child);
#endif
static inline Sender *setCurrentSender(QObject *receiver,
Sender *sender); // 設置當前發送者
static inline void resetCurrentSender(QObject *receiver,
Sender *currentSender,
Sender *previousSender); // 重置當前發送者
static int *setDeleteWatch(QObjectPrivate *d, int *newWatch); // 設置刪除監聽
static void resetDeleteWatch(QObjectPrivate *d, int *oldWatch, int deleteWatch); // 重置刪除監聽
static void clearGuards(QObject *); // 清除管理者
static QObjectPrivate *get(QObject *o) { // 從QObject對象中獲取QObjectPrivate
return o->d_func();
}
int signalIndex(const char *signalName) const; // 信號索引
inline bool isSignalConnected(uint signalIdx) const; // 判斷是否為信號連接
public:
QString objectName; // 對象名字
ExtraData *extraData; // extra data set by the user // 額外數據
QThreadData *threadData; // id of the thread that owns the object // 線程數據
QObjectConnectionListVector *connectionLists; // 連接列表數組
Connection *senders; // linked list of connections connected to this object // 發送者連接
Sender *currentSender; // object currently activating the object // 當前發送者
mutable quint32 connectedSignals[2]; // 連接信號
#ifdef QT3_SUPPORT
QList<QObject *> pendingChildInsertedEvents;
#else
// preserve binary compatibility with code compiled without Qt 3 support
// keeping the binary layout stable helps the Qt Creator debugger
void *unused; // 保留
#endif
QList<QPointer<QObject> > eventFilters;
union {
QObject *currentChildBeingDeleted; // 當前子節點被刪除
QAbstractDeclarativeData *declarativeData; //extra data used by the declarative module
};
// these objects are all used to indicate that a QObject was deleted
// plus QPointer, which keeps a separate list
QAtomicPointer<QtSharedPointer::ExternalRefCountData> sharedRefcount; // 共享引用計數
int *deleteWatch; // 刪除監聽者
};

QObjectPrivate從QObjectData派生下來：

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class
#if defined(__INTEL_COMPILER) && defined(Q_OS_WIN)
Q_CORE_EXPORT
#endif
QObjectData {
public:
virtual ~QObjectData() = 0;
QObject *q_ptr; // 當前指向的QOBject
QObject *parent; // 指向的QObject父類
QObjectList children; // 孩兒們
uint isWidget : 1; // 是否為widget的標記
uint pendTimer : 1; // 開啟時鐘
uint blockSig : 1; // 阻塞信號標記
uint wasDeleted : 1; // 是否參數標記
uint ownObjectName : 1; // 是否含有對象名標記
uint sendChildEvents : 1; // 發送到子對象時間標記
uint receiveChildEvents : 1; // 接受子對象時間標記
uint inEventHandler : 1; // 是否有事件句柄標記
uint inThreadChangeEvent : 1; // 線程更改時間標記
//是否有守護標記
uint hasGuards : 1; //true iff there is one or more QPointer attached to this object
uint unused : 22; // 保留
int postedEvents; // 發送的數據
QMetaObject *metaObject; // assert dynamic // 元對象
};

QObjectData保留一些了基本的數據信息

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#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;

在元對象中獲取類名和父類的方式很簡單，直接即可。

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

元對象中cast函數的實現

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QObject *QMetaObject::cast(QObject *obj) const
{
if (obj) {
const QMetaObject *m = obj->metaObject();
do {
if (m == this)
return const_cast<QObject*>(obj);
} while ((m = m->d.superdata));
}
return 0;
}

如果對象obj存在，則對每一個obj的父類的源對象進行轉換，如果是當前的元對象，則進行返回，否則返回0，也就是cast函數是在obj中查找當前元對象所在的QObject對象。

posted on 2014-05-22 15:58 lyhui 閱讀(380) 評論(0) 收藏舉報

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