Qt Moc及信号-槽源代码解析
燕和裕
版本Qt5.12.3 moc_test.cpp位于可执行文件目录下，其余源代码都位于Qt5.12.3\5.12.3\Src\qtbase\src\corelib\kernel
一. MOC
1.1 简介
元对象编译器moc(Meta-Object Compiler)是Qt对C++的扩展。可以先把它看作一个代码生成器。以test类为例，构建项目时，moc读取C++头文件。如果在test.h中找到Q_OBJECT宏，它将生成一个moc_test.cpp，其中包含test类的元对象(metaObject)代码。这个新的文件和test.cpp一起参与编译，最终被链接到二进制代码中去。
Qt 将源代码交给标准 C++编译器，如gcc之前，需要事先将扩展的语法(Q_OBJECT,SLOT,SIGNAL等)展开来。完成这一操作的就是moc。
可以在命令行下输入moc test.h -o moc_test.cpp手动生成。
1.2 宏
Q_OBJECT,SLOT,SIGNAL,emit, Q_INVOKABLE等宏是Qt扩展的语法，它们其实定义在qobjectdefs.h中，编译时被moc展开。
二. moc_test.cpp分析
先贴一下代码：
test.h
class test : public QObject
{
Q_OBJECT
public:
explicit test(QObject *parent = nullptr);
int getValue(){return m_value;}
Q_INVOKABLE void identifyByMoc();
signals:
void testSignal1();
void testSignal2();
void testSignal3();
void valueChanged(int newValue);
public slots:
void testSlot1();
void testSlot2();
void setValue(int value);
private:
int m_value;
};test.cpp
#include "test.h"
test::test(QObject *parent) : QObject(parent)
{
m_value = 0;
}
void test::identifyByMoc(){
qDebug()<<"Identified By Moc";
}
void test::testSlot1(){
qDebug()<<"Invoke testSlot1";
}
void test::testSlot2(){
qDebug()<<"Invoke testSlot2";
}
void test::setValue(int value)
{
m_value = value;
emit valueChanged(value);
}main.cpp
#include “test.h”
void test_value()
{
test a,b;
QObject::connect(&a,SIGNAL(valueChanged(int)),&b,SLOT(setValue(int)));
QObject::connect(&a,SIGNAL(valueChanged(int)),&a,SLOT(testSlot1()));
qDebug()<<SIGNAL(valueChanged(int))<<SLOT(setValue(int));
qDebug()<<"before: b.getValue ="<<b.getValue();
a.setValue(12);
qDebug()<<"after: b.getValue ="<<b.getValue();
}moc_test.cpp
/****************************************************************************
** Meta object code from reading C++ file 'test.h'
**
** Created by: The Qt Meta Object Compiler version 67 (Qt 5.12.3)
**
** WARNING! All changes made in this file will be lost!
*****************************************************************************/
#include "../../mocTest/test.h"
#include <QtCore/qbytearray.h>
#include <QtCore/qmetatype.h>
#if !defined(Q_MOC_OUTPUT_REVISION)
#error "The header file 'test.h' doesn't include <QObject>."
#elif Q_MOC_OUTPUT_REVISION != 67
#error "This file was generated using the moc from 5.12.3. It"
#error "cannot be used with the include files from this version of Qt."
#error "(The moc has changed too much.)"
#endif
QT_BEGIN_MOC_NAMESPACE
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
//此处省略见下文
QT_WARNING_POP
QT_END_MOC_NAMESPACEmoc_test.cpp看起来很复杂，分三部分来看：
2.1 类信息
位于moc_test.cpp头部
struct qt_meta_stringdata_test_t { //定义保存类信息的结构体
QByteArrayData data[12];
char stringdata0[113];
};QT_MOC_LITERAL宏的作用是为stringdata0中保存的每个函数名都创建一个QByteArrayData，宏参数为函数的索引值，偏移量，函数名长度。
#define QT_MOC_LITERAL(idx, ofs, len \
Q_STATIC_BYTE_ARRAY_DATA_HEADER_INITIALIZER_WITH_OFFSET(len, \
qptrdiff(offsetof(qt_meta_stringdata_test_t, stringdata0) + ofs \
- idx * sizeof(QByteArrayData)) \
)
static const qt_meta_stringdata_test_t
qt_meta_stringdata_test = { //初始化保存类信息的结构体
{
QT_MOC_LITERAL(0, 0, 4), // "test"
QT_MOC_LITERAL(1, 5, 11), // "testSignal1"
QT_MOC_LITERAL(2, 17, 0), // ""
QT_MOC_LITERAL(3, 18, 11), //"testSignal2"
QT_MOC_LITERAL(4, 30, 11), //"testSignal3"
QT_MOC_LITERAL(5, 42, 12), // "valueChanged"
QT_MOC_LITERAL(6, 55, 8), //"newValue"
QT_MOC_LITERAL(7, 64, 9), //"testSlot1"
QT_MOC_LITERAL(8, 74, 9), //"testSlot2"
QT_MOC_LITERAL(9, 84, 8), //"setValue"
QT_MOC_LITERAL(10, 93, 5), //"value"
QT_MOC_LITERAL(11, 99, 13) //"identifyByMoc
},
"test\0testSignal1\0\0testSignal2\0testSignal3\0"
"valueChanged\0newValue\0testSlot1\0"
"testSlot2\0setValue\0value\0identifyByMoc"
};
#undef QT_MOC_LITERAL
static const uint qt_meta_data_test[] = {
//保存了信号，槽及moc识别的其他函数的个数，函数索引，返回类型，参数个数，参数类型等信息。
//content:
8, // revision
0, // classname
0, 0, // classinfo
8, 14, // methods
0, 0, // properties
0, 0, // enums/sets
0, 0, // constructors
0, // flags
4, // signalCount
//signals: name, argc, parameters, tag, flags
1, 0, 54, 2, 0x06 /* Public */,
3, 0, 55, 2, 0x06 /* Public */,
4, 0, 56, 2, 0x06 /* Public */,
5, 1, 57, 2, 0x06 /* Public */,
//slots: name, argc, parameters, tag, flags
7, 0, 60, 2, 0x0a /* Public */,
8, 0, 61, 2, 0x0a /* Public */,
9, 1, 62, 2, 0x0a /* Public */,
//methods: name, argc, parameters, tag, flags
11, 0, 65, 2, 0x02 /* Public */,
//signals: parameters
QMetaType::Void,
QMetaType::Void,
QMetaType::Void,
QMetaType::Void, QMetaType::Int, 6,
//slots: parameters
QMetaType::Void,
QMetaType::Void,
QMetaType::Void, QMetaType::Int, 10,
//methods: parameters
QMetaType::Void,
0 // eod
};2.2 signals实现
位于moc_test.cpp底部：
// SIGNAL 0
void test::testSignal1()
{
QMetaObject::activate(this, &staticMetaObject, 0, nullptr);
}
// SIGNAL 1
void test::testSignal2()
{
QMetaObject::activate(this, &staticMetaObject, 1, nullptr);
}
// SIGNAL 2
void test::testSignal3()
{
QMetaObject::activate(this, &staticMetaObject, 2, nullptr);
}
// SIGNAL 3
void test::valueChanged(int _t1)
{
void *_a[] = { nullptr,const_cast<void*>(reinterpret_cast<const void*>(&_t1)) };
QMetaObject::activate(this, &staticMetaObject, 3, _a);
}test.h中构造函数一个，普通函数一个(getValue)，signal四个，slot三个，Q_INVOKABLE修饰的方法一个。其中三个槽函数需要自己在test.cpp里实现，四个信号函数由moc自动在moc_test.cpp中实现，在注释可以看到索引根据声明顺序分别为0，1，2，3。
2.3 Q_OBJECT宏的展开
查找qobjectdefs.h,可以找到Q_OBJECT宏的定义
#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,
"")正对应moc_test.cpp里的函数等，我们取重要的几个：
位于moc_test.cpp中部：
2.3.1 qt_static_metacall
void test::qt_static_metacall(QObject *_o,QMetaObject::Call _c, int _id, void **_a)
{
if (_c == QMetaObject::InvokeMetaMethod) {
auto *_t = static_cast<test *>(_o);
Q_UNUSED(_t)
switch (_id) {
case 0: _t->testSignal1(); break;
case 1: _t->testSignal2(); break;
case 2: _t->testSignal3(); break;
case 3: _t->valueChanged((*reinterpret_cast< int(*)>(_a[1])));break;
case 4: _t->testSlot1(); break;
case 5: _t->testSlot2(); break;
case 6: _t->setValue((*reinterpret_cast< int(*)>(_a[1])));break;
case 7: _t->identifyByMoc(); break;
default: ;
}
}else if (_c == QMetaObject::IndexOfMethod) {
int *result = reinterpret_cast<int *>(_a[0]);
{
using _t = void (test::*)();
if (*reinterpret_cast<_t *>(_a[1]) ==static_cast<_t>(&test::testSignal1)) {
*result = 0;
return;
}
}
{
using _t = void (test::*)();
if (*reinterpret_cast<_t*>(_a[1]) == static_cast<_t>(&test::testSignal2)) {
*result = 1;
return;
}
}
{
using _t = void (test::*)();
if (*reinterpret_cast<_t *>(_a[1]) ==
static_cast<_t>(&test::testSignal3)) {
*result = 2;
return;
}
}
{
using _t = void (test::*)(int );
if (*reinterpret_cast<_t *>(_a[1]) ==
static_cast<_t>(&test::valueChanged)) {
*result = 3;
return;
}
}
}
}根据函数索引调用槽函数，在这里可以看出信号函数也可以当作槽函数一样被调用，这也是信号槽调用过程的最后一步(先留个印象)
2.3.2 staticMetaObject
test类的元对象(QMetaObject)，保存了test类的信息。保存的数据qt_meta_stringdata_test.data及qt_meta_data_test在moc文件的顶部定义并初始化。
QT_INIT_METAOBJECT const QMetaObject test::staticMetaObject = { {
&QObject::staticMetaObject,
qt_meta_stringdata_test.data,
qt_meta_data_test,
qt_static_metacall,
nullptr,
nullptr
} };2.3.3 metaObject
返回当前的QMetaObject,一般是返回staticMetaObject,即2介绍的。
const QMetaObject *test::metaObject() const
{
return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
}2.3.4 qt_metacast
类型转换
void *test::qt_metacast(const char *_clname)
{
if (!_clname) return nullptr;
if (!strcmp(_clname, qt_meta_stringdata_test.stringdata0))
return static_cast<void*>(this);
return QObject::qt_metacast(_clname);
}2.3.5 qt_metacall
int test::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 < 8)
qt_static_metacall(this, _c, _id, _a);
_id -= 8;
}else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
if (_id < 8)
*reinterpret_cast<int*>(_a[0]) = -1;
_id -= 8;
}
return _id;
}在内部调用了qt_static_metacall
总结：Moc的作用就是把Q_OBJECT SIGNAL Q_INVOKABLE等宏展开，并保存类中特定函数(signals,slots标签下的函数及Q_INVOKABLE修饰的函数等)的信息，创建函数的回调。
三. connect
要使用Qt的信号-槽机制，必须要connect这一步。我们查看QObject::connect的源码：
QObject.cpp
QMetaObject::Connection
QObject::connect(const QObject *sender, const char *signal,
constQObject *receiver, const char *method, Qt::ConnectionType type)
{
//此处省略了函数参数检查，信号及槽函数索引获取，connect类型处理等代码。
//最后其实调用了QMetaObjectPrivate::connect
QMetaObject::Connection handle = QMetaObject::Connection(QMetaObjectPrivate::connect(
sender, signal_index, smeta, receiver, method_index_relative, rmeta ,type, types));
return handle;
}QMetaObjectPrivate::connect同样位于QObject.cpp
QObjectPrivate::Connection *QMetaObjectPrivate::connect(const QObject *sender,
int signal_index, const QMetaObject *smeta,
const QObject *receiver, int method_index,
const QMetaObject *rmeta, int type, int *types)
{
QObject *s = const_cast<QObject *>(sender);
QObject *r = const_cast<QObject *>(receiver);
int method_offset = rmeta ? rmeta->methodOffset() : 0;
Q_ASSERT(!rmeta || QMetaObjectPrivate::get(rmeta)->revision >= 6);
QObjectPrivate::StaticMetaCallFunction callFunction =
rmeta ? rmeta->d.static_metacall : 0;
QOrderedMutexLocker locker(signalSlotLock(sender),
signalSlotLock(receiver));
if (type & Qt::UniqueConnection) {
QObjectConnectionListVector *connectionLists =QObjectPrivate::get(s)->connectionLists;
if (connectionLists && connectionLists->count() >signal_index) {
const QObjectPrivate::Connection *c2 = (*connectionLists)[signal_index].first;
int method_index_absolute = method_index + method_offset;
while (c2) {
if (!c2->isSlotObject && c2->receiver == receiver && c2->method() == method_index_absolute)
return 0;
c2 = c2->nextConnectionList;
}
}
type &= Qt::UniqueConnection - 1;
}
// QObjectPrivate::Connection实例化，
//存储了信号-槽链接的信息
QScopedPointer<QObjectPrivate::Connection> c(new QObjectPrivate::Connection);
c->sender = s;
c->signal_index = signal_index;
c->receiver = r;
c->method_relative = method_index;
c->method_offset = method_offset;
c->connectionType = type;
c->isSlotObject = false;
c->argumentTypes.store(types);
c->nextConnectionList = 0;
c->callFunction = callFunction;
//addConnection为信号发送者s保存了这个信号-槽链接，具体保存了什么，还需要
//分析QObjectPrivate::Connection以及QObjectPrivate::addConnection
QObjectPrivate::get(s)->addConnection(signal_index, c.data());
locker.unlock();
QMetaMethod smethod = QMetaObjectPrivate::signal(smeta, signal_index);
if (smethod.isValid())
s->connectNotify(smethod);
return c.take();
}qobject_p.h中定义了class QObjectPrivate
它的几个成员如下：
struct Connection
{
QObject *sender;
QObject *receiver;
union {
StaticMetaCallFunction callFunction;
QtPrivate::QSlotObjectBase *slotObj;
};
// The next pointer for the singly-linked ConnectionList
Connection *nextConnectionList;
//senders linked list
Connection *next;
Connection **prev;
ushort method_offset;
ushort method_relative;
uint signal_index : 27; // In signal range (see QObjectPrivate::signalIndex())
ushort connectionType : 3; // 0 == auto, 1 == direct, 2 == queued, 4 == blocking
//省略部分代码
};Connection结构体保存了一个连接。其中的信息包括信号发送者指针，信号接收者指针以及指向下一个Connection的指针，信号索引，连接类型等
一个信号可以对应多个槽函数，这里用ConnectionList保存一个信号对应的所有连接。它是一个单向链表，每个节点都是一个Connection，通过它内部的nextConnectionList指针指向下一个Connection。在这里仅保存头尾指针即可。
struct ConnectionList {
ConnectionList() : first(nullptr), last(nullptr) {}
Connection *first;
Connection *last;
};connectionLists保存此对象作为信号发送者所对应的所有连接。这个向量里每个元素都是一个ConnectionList单链表
QObjectConnectionListVector *connectionLists;QObject.cpp里定义了QObjectConnectionListVector
class QObjectConnectionListVector : public
QVector<QObjectPrivate::ConnectionList>
{
public:
bool orphaned; //the QObject owner of this vector has been destroyed while the vector was inUse
bool dirty; //some Connection have been disconnected (their receiver is 0) but not removed from the list yet
int inUse; //number of functions that are currently accessing this object or its connections
QObjectPrivate::ConnectionList allsignals;
QObjectConnectionListVector(): QVector<QObjectPrivate::ConnectionList>(), orphaned(false),
dirty(false), inUse(0)
{}
QObjectPrivate::ConnectionList &operator[](int at)
{
if (at < 0)
return allsignals;
return QVector<QObjectPrivate::ConnectionList>::operator[](at);
}
};Connection *next和Connection**prev是此对象作为信号接收者时，保存发送者的双向链表的操作指针，这里的内容待以后补充。
接下来看最后的addConnection, 位于QObject.cpp
void QObjectPrivate::addConnection(int signal, Connection *c)
{
Q_ASSERT(c->sender == q_ptr);
if (!connectionLists)
connectionLists = new QObjectConnectionListVector();
if (signal >= connectionLists->count())
connectionLists->resize(signal + 1);
//根据信号索引取得此信号所对应的链表，并把此连接加入链表中。
ConnectionList &connectionList = (*connectionLists)[signal];
if (connectionList.last) {
connectionList.last->nextConnectionList = c;
}else {
connectionList.first = c;
}
connectionList.last = c;
cleanConnectionLists();
//下面是对Connection* QObjectPrivate::senders双向链表的操作
c->prev = &(QObjectPrivate::get(c->receiver)->senders);
c->next = *c->prev;
*c->prev = c;
if (c->next)
c->next->prev = &c->next;
if (signal < 0) {
connectedSignals[0] = connectedSignals[1] = ~0;
}else if (signal < (int)sizeof(connectedSignals) * 8) {
connectedSignals[signal >> 5] |= (1 << (signal & 0x1f));
}
}四. activate
连接完成后，我们调用信号函数，从moc_test.cpp里对信号函数的实现可知，其实是调用了QMetaObject::activate(this, &staticMetaObject, 3, _a);
// SIGNAL 3
void test::valueChanged(int _t1)
{
void *_a[] = { nullptr, const_cast<void*>(reinterpret_cast<const void*>(&_t1)) };
QMetaObject::activate(this, &staticMetaObject, 3, _a);
}QMetaObject::activate源码在QObject.cpp中
void QMetaObject::activate(QObject *sender, const QMetaObject *m, int local_signal_index, void **argv)
{
activate(sender, QMetaObjectPrivate::signalOffset(m), local_signal_index, argv);
}下面的activate函数省略了部分代码，方便理解。
void QMetaObject::activate(QObject *sender, int signalOffset, int local_signal_index, void **argv)
{
int signal_index = signalOffset + local_signal_index;
//判断是否有与该信号相连接的接收对象
if(!sender->d_func()->isSignalConnected(signal_index))
return; // nothing connected to these signals, and no spy
//给信号量加锁，因为在connectionLists里所有的操作都是线程安全的
QMutexLocker locker(signalSlotLock(sender));
//获取与该信号的ConnectionList链表
QObjectConnectionListVector *connectionLists = sender->d_func()->connectionLists;
const QObjectPrivate::ConnectionList *list = &connectionLists->at(signal_index);
QObjectPrivate::Connection *c = list->first;
if (!c) continue;
QObjectPrivate::Connection *last = list->last;
//循环执行该信号对应的所有槽函数
do {
if (!c->receiver)
continue;
QObject * const receiver = c->receiver;
const bool receiverInSameThread = QThread::currentThreadId() == receiver->d_func()->threadData->threadId;
// 决定该连接是马上响应还是把它放到事件队列中
if ((c->connectionType == Qt::AutoConnection && !receiverInSameThread)|| (c->connectionType == Qt::QueuedConnection)) {
queued_activate(sender, signal_index, c, argv);
continue;
} else if (c->connectionType == Qt::BlockingQueuedConnection) {
continue;
}
QConnectionSenderSwitcher sw;
if (receiverInSameThread)
sw.switchSender(receiver, sender, signal_index);
const QObjectPrivate::StaticMetaCallFunction callFunction = c->callFunction;
const int method_relative = c->method_relative;
//下面if-else结构包含三种调用槽函数的方式。
if (c->isSlotObject) {
c->slotObj->ref();
QScopedPointer<QtPrivate::QSlotObjectBase,QSlotObjectBaseDeleter>obj(c->slotObj);
locker.unlock();
Q_TRACE(QMetaObject_activate_begin_slot_functor, obj.data());
//一，通过call调用接收者中的槽函数
obj->call(receiver, argv ? argv : empty_argv);
Q_TRACE(QMetaObject_activate_end_slot_functor, obj.data());
obj.reset();
locker.relock();
} else if (c->callFunction && c->method_offset <= receiver->metaObject()->methodOffset()) {
const int methodIndex = c->method();
const int method_relative = c->method_relative;
const auto callFunction = c->callFunction;
locker.unlock();
if(qt_signal_spy_callback_set.slot_begin_callback != 0)
qt_signal_spy_callback_set.slot_begin_callback(receiver, methodIndex, argv ? argv : empty_argv);
Q_TRACE(QMetaObject_activate_begin_slot, receiver, methodIndex);
//二，callFunction即moc_test.cpp里的qt_static_metacall
callFunction(receiver, QMetaObject::InvokeMetaMethod, method_relative, argv ? argv : empty_argv);
Q_TRACE(QMetaObject_activate_end_slot, receiver, methodIndex);
if(qt_signal_spy_callback_set.slot_end_callback != 0)
qt_signal_spy_callback_set.slot_end_callback(receiver, methodIndex);
locker.relock();
} else {
const int method = c->method_relative + c->method_offset;
locker.unlock();
if(qt_signal_spy_callback_set.slot_begin_callback != 0) {
qt_signal_spy_callback_set.slot_begin_callback(receiver, method,argv ? argv : empty_argv);
}
Q_TRACE(QMetaObject_activate_begin_slot, receiver, method);
//三，metacall即moc_test.cpp里的qt_metacall
metacall(receiver, QMetaObject::InvokeMetaMethod, method, argv ? argv : empty_argv);
Q_TRACE(QMetaObject_activate_end_slot, receiver, method);
if(qt_signal_spy_callback_set.slot_end_callback != 0)
qt_signal_spy_callback_set.slot_end_callback(receiver,method);
locker.relock();
} // 检查该对象没有被槽函数删除
if (connectionLists->orphaned) break;
} while (c != last && (c = c->nextConnectionList) != 0);
}第二种方法解析：
qobjectdefs.h
struct Q_CORE_EXPORT QMetaObject
{
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;
}moc_test.cpp 用qt_static_metacall实例化d.static_metacall
QT_INIT_METAOBJECT const QMetaObject
test::staticMetaObject = { {
&QObject::staticMetaObject,
qt_meta_stringdata_test.data,
qt_meta_data_test,
qt_static_metacall,
nullptr,
nullptr
} };qobject.cpp
QObjectPrivate::Connection *QMetaObjectPrivate::connect()
{
QObjectPrivate::StaticMetaCallFunction callFunction = rmeta ? rmeta->d.static_metacall : 0;
}
void QMetaObject::activate()
{
const QObjectPrivate::StaticMetaCallFunction callFunction = c->callFunction;
callFunction(...);
//最后调用callFunction其实就是调用qt_static_metacall，还记的文章前边说的留个印象么，现在就到了调用的最后一步。
}第三种方法解析：
qmetaobject.cpp
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);
}moc_test.cpp
int test::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 < 8)
qt_static_metacall(this, _c, _id, _a);
_id -= 8;
}else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
if (_id < 8)
*reinterpret_cast<int*>(_a[0]) = -1;
_id -= 8;
}
return _id;
}qobject.cpp
void QMetaObject::activate()
{
metacall(receiver, QMetaObject::InvokeMetaMethod, method, argv ? argv : empty_argv);
}metacall其实就是调用qt_metacall，在内部最终还是调用了qt_static_metacall
五. 总结
5.1 解析
Moc帮我们解析头文件中Qt特有的宏，将函数信息保存在数组中，构建信号函数的实现，槽函数的回调。
5.2 保存
QObject::connect将连接信息保存在结构体Connection中，一个信号可对应多个槽函数，这就形成了单链表ConnectionList，然后以信号在test类的MetaObject中的索引作为向量的索引保存所有链表，形成QObjectConnectionListVector* connectionLists.
5.3 调用
调用信号函数时，其实是调用activate函数，最终回到qt_static_metacall，调用槽函数。
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