信号槽连接
目录
信号槽的连接,其实内部本质还是一个回调函数,主要是维护了信号发送Object的元对象里一个连接的列表。调用connect函数时,将槽的一系列信息,封装成一个Connection,在发送信号时,通过这个列表,去回调槽函数。
1. 信号的连接
下面列举一种信号的连接方式,来大致讲解一下信号的连接过程。- //Connect a signal to a pointer to qobject member function
- // QtPrivate::FunctionPointer<Func1>::Object返回发送信号的对象类型
- template <typename Func1, typename Func2>
- static inline QMetaObject::Connection connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal,
- const typename QtPrivate::FunctionPointer<Func2>::Object *receiver, Func2 slot,
- Qt::ConnectionType type = Qt::AutoConnection)
- {
- typedef QtPrivate::FunctionPointer<Func1> SignalType;
- typedef QtPrivate::FunctionPointer<Func2> SlotType;
- Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
- "No Q_OBJECT in the class with the signal");
- //compilation error if the arguments does not match.
- // 检查信号和槽参数是否一致
- Q_STATIC_ASSERT_X(int(SignalType::ArgumentCount) >= int(SlotType::ArgumentCount),
- "The slot requires more arguments than the signal provides.");
- // 检查信号和槽参数是否兼容
- Q_STATIC_ASSERT_X((QtPrivate::CheckCompatibleArguments<typename SignalType::Arguments, typename SlotType::Arguments>::value),
- "Signal and slot arguments are not compatible.");
- // 检查信号和槽的返回值是否兼容
- Q_STATIC_ASSERT_X((QtPrivate::AreArgumentsCompatible<typename SlotType::ReturnType, typename SignalType::ReturnType>::value),
- "Return type of the slot is not compatible with the return type of the signal.");
- const int *types = nullptr;
- // SignalType -> QtPrivate::FunctionPointer<Func1>
- // QtPrivate::ConnectionTypes<typename SignalType::Arguments>::types() 返回信号参数的值对应的元类型id列表
- if (type == Qt::QueuedConnection || type == Qt::BlockingQueuedConnection)
- types = QtPrivate::ConnectionTypes<typename SignalType::Arguments>::types();
- return connectImpl(sender, reinterpret_cast<void **>(&signal),
- receiver, reinterpret_cast<void **>(&slot),
- new QtPrivate::QSlotObject<Func2, typename QtPrivate::List_Left<typename SignalType::Arguments, SlotType::ArgumentCount>::Value,
- typename SignalType::ReturnType>(slot),
- type, types, &SignalType::Object::staticMetaObject);
- }
复制代码 上面主要都是一些基本的信号连接的判断,主要是:
- 信号和槽的参数数量
- 信号和槽的参数是否兼容
- 信号和槽的返回值是否兼容
然后获取信号参数所对应的元类型Id,再就到了一个信号连接的具体内部实现中- QMetaObject::Connection QObject::connectImpl(const QObject *sender, void **signal,
- const QObject *receiver, void **slot,
- QtPrivate::QSlotObjectBase *slotObj, Qt::ConnectionType type,
- const int *types, const QMetaObject *senderMetaObject)
- {
- if (!signal) {
- qWarning("QObject::connect: invalid nullptr parameter");
- if (slotObj)
- slotObj->destroyIfLastRef();
- return QMetaObject::Connection();
- }
- int signal_index = -1;
- void *args[] = { &signal_index, signal };
- // 根据调用来判断是否存在信号,如果当前类没有就去父类中寻找
- // 直到找到信号或者是最基层的类
- // 找到信号的index和信号的对象
- for (; senderMetaObject && signal_index < 0; senderMetaObject = senderMetaObject->superClass()) {
- senderMetaObject->static_metacall(QMetaObject::IndexOfMethod, 0, args);
- if (signal_index >= 0 && signal_index < QMetaObjectPrivate::get(senderMetaObject)->signalCount)
- break;
- }
- if (!senderMetaObject) {
- qWarning("QObject::connect: signal not found in %s", sender->metaObject()->className());
- slotObj->destroyIfLastRef();
- return QMetaObject::Connection(nullptr);
- }
- // 信号下标
- signal_index += QMetaObjectPrivate::signalOffset(senderMetaObject);
- return QObjectPrivate::connectImpl(sender, signal_index, receiver, slot, slotObj, type, types, senderMetaObject);
- }
复制代码 同样,我们对这个函数进行分析,第一个片段是对信号发送者是否为空指针的一个判断- if (!signal) {
- qWarning("QObject::connect: invalid nullptr parameter");
- if (slotObj)
- slotObj->destroyIfLastRef();
- return QMetaObject::Connection();
- }
复制代码 第二个片段是去找到信号发送者(sender)的元对象类型(Meta Object)以及信号在对象信号中的位置。如果当前对象没有该信号,就去其父类对象去找。直到找到为止。- for (; senderMetaObject && signal_index < 0; senderMetaObject = senderMetaObject->superClass()) {
- senderMetaObject->static_metacall(QMetaObject::IndexOfMethod, 0, args);
- if (signal_index >= 0 && signal_index < QMetaObjectPrivate::get(senderMetaObject)->signalCount)
- break;
- }
复制代码 然后就是进一步调用其内部实现:- QMetaObject::Connection QObjectPrivate::connectImpl(const QObject *sender, int signal_index,
- const QObject *receiver, void **slot,
- QtPrivate::QSlotObjectBase *slotObj, Qt::ConnectionType type,
- const int *types, const QMetaObject *senderMetaObject)
- {
- // 发送对象、接收对象、槽函数对象、信号发送的元对象都不为空 2023-3-11
- if (!sender || !receiver || !slotObj || !senderMetaObject) {
- // 任意一个为空,报错且清理空间,并返回
- const char *senderString = sender ? sender->metaObject()->className()
- : senderMetaObject ? senderMetaObject->className()
- : "Unknown";
- const char *receiverString = receiver ? receiver->metaObject()->className()
- : "Unknown";
- qWarning("QObject::connect(%s, %s): invalid nullptr parameter", senderString, receiverString);
- if (slotObj)
- slotObj->destroyIfLastRef();
- return QMetaObject::Connection();
- }
- // 去掉const的发送和接受对象
- QObject *s = const_cast<QObject *>(sender);
- QObject *r = const_cast<QObject *>(receiver);
- // 顺序锁,按照顺序依次去对mutex去上锁
- // 这里依次对发送和接收者的信号去上锁
- QOrderedMutexLocker locker(signalSlotLock(sender),
- signalSlotLock(receiver));
- if (type & Qt::UniqueConnection && slot && QObjectPrivate::get(s)->connections.loadRelaxed()) {
- // ObjectPrivate::get(s) 获取s对应的d指针
- // connections 维护了所有的信号槽连接
- QObjectPrivate::ConnectionData *connections = QObjectPrivate::get(s)->connections.loadRelaxed();
- if (connections->signalVectorCount() > signal_index) {
- // 获取信号的连接
- const QObjectPrivate::Connection *c2 = connections->signalVector.loadRelaxed()->at(signal_index).first.loadRelaxed();
- // 循环遍历
- while (c2) {
- // 如果已经存在信号和槽的连接,且为uniqueConnection,则返回
- if (c2->receiver.loadRelaxed() == receiver && c2->isSlotObject && c2->slotObj->compare(slot)) {
- slotObj->destroyIfLastRef();
- return QMetaObject::Connection();
- }
- c2 = c2->nextConnectionList.loadRelaxed();
- }
- }
- // 将type与UniqueConnection进行异或,去掉UniqueConnection
- type = static_cast<Qt::ConnectionType>(type ^ Qt::UniqueConnection);
- }
- // 创建一个新的连接
- std::unique_ptr<QObjectPrivate::Connection> c{new QObjectPrivate::Connection};
- c->sender = s;
- c->signal_index = signal_index;
- QThreadData *td = r->d_func()->threadData;
- td->ref();
- c->receiverThreadData.storeRelaxed(td);
- c->receiver.storeRelaxed(r);
- c->slotObj = slotObj;
- c->connectionType = type;
- c->isSlotObject = true;
- if (types) {
- c->argumentTypes.storeRelaxed(types);
- c->ownArgumentTypes = false;
- }
- // 将新创建的连接加到连接列表中
- QObjectPrivate::get(s)->addConnection(signal_index, c.get());
- QMetaObject::Connection ret(c.release());
- locker.unlock();
- QMetaMethod method = QMetaObjectPrivate::signal(senderMetaObject, signal_index);
- Q_ASSERT(method.isValid());
- s->connectNotify(method);
- return ret;
- }
复制代码 同样第一个部分也是对一些个空值的判断- // 发送对象、接收对象、槽函数对象、信号发送的元对象都不为空 2023-3-11
- if (!sender || !receiver || !slotObj || !senderMetaObject) {
- // 任意一个为空,报错且清理空间,并返回
- const char *senderString = sender ? sender->metaObject()->className()
- : senderMetaObject ? senderMetaObject->className()
- : "Unknown";
- const char *receiverString = receiver ? receiver->metaObject()->className()
- : "Unknown";
- qWarning("QObject::connect(%s, %s): invalid nullptr parameter", senderString, receiverString);
- if (slotObj)
- slotObj->destroyIfLastRef();
- return QMetaObject::Connection();
- }
复制代码 然后就是一个if判断,主要是对Qt::UniqueConnection连接的一些处理,获取当前对象的信号连接列表,并判断当前要连接的信号和槽,之前有没有被连接过,如果有过连接,就直接返回。- if (type & Qt::UniqueConnection && slot && QObjectPrivate::get(s)->connections.loadRelaxed()) {
- // ObjectPrivate::get(s) 获取s对应的d指针
- // connections 维护了所有的信号槽连接
- QObjectPrivate::ConnectionData *connections = QObjectPrivate::get(s)->connections.loadRelaxed();
- if (connections->signalVectorCount() > signal_index) {
- // 获取信号的连接
- const QObjectPrivate::Connection *c2 = connections->signalVector.loadRelaxed()->at(signal_index).first.loadRelaxed();
- // 循环遍历
- while (c2) {
- // 如果已经存在信号和槽的连接,且为uniqueConnection,则返回
- if (c2->receiver.loadRelaxed() == receiver && c2->isSlotObject && c2->slotObj->compare(slot)) {
- slotObj->destroyIfLastRef();
- return QMetaObject::Connection();
- }
- c2 = c2->nextConnectionList.loadRelaxed();
- }
- }
- // 将type与UniqueConnection进行异或,去掉UniqueConnection
- type = static_cast<Qt::ConnectionType>(type ^ Qt::UniqueConnection);
- }
复制代码 最后才是创建一个Connection并将连接的信息以及信号的参数设置进去,然后保存到对象的信号连接容器里。- // 创建一个新的连接
- std::unique_ptr<QObjectPrivate::Connection> c{new QObjectPrivate::Connection};
- c->sender = s;
- c->signal_index = signal_index;
- QThreadData *td = r->d_func()->threadData;
- td->ref();
- c->receiverThreadData.storeRelaxed(td);
- c->receiver.storeRelaxed(r);
- c->slotObj = slotObj;
- c->connectionType = type;
- c->isSlotObject = true;
- if (types) {
- c->argumentTypes.storeRelaxed(types);
- c->ownArgumentTypes = false;
- }
- // 将新创建的连接加到连接列表中
- QObjectPrivate::get(s)->addConnection(signal_index, c.get());
- QMetaObject::Connection ret(c.release());
- locker.unlock();
- QMetaMethod method = QMetaObjectPrivate::signal(senderMetaObject, signal_index);
- Q_ASSERT(method.isValid());
- s->connectNotify(method);
- return ret;
复制代码 2 槽的调用
定义一个信号,使用moc生成moc文件之后,我们可以看到信号函数的定义如下:- // SIGNAL 0
- void MainWindow::sgnTestFor()
- {
- QMetaObject::activate(this, &staticMetaObject, 0, nullptr);
- }
复制代码 我们发射一个信号的时候,我们会这样写:我们可以看关于emit的定义:
其实emit关键字什么都没有做,只是标识了一下当前发射了信号。所以本质上,发射一个信号实际上就是直接调用了这个信号的函数,也就是调用了QMetaObject中的activate函数。
函数如下:- void QMetaObject::activate(QObject *sender, const QMetaObject *m, int local_signal_index,
- void **argv)
- {
- int signal_index = local_signal_index + QMetaObjectPrivate::signalOffset(m);
- if (Q_UNLIKELY(qt_signal_spy_callback_set.loadRelaxed()))
- doActivate<true>(sender, signal_index, argv);
- else
- doActivate<false>(sender, signal_index, argv);
- }
复制代码 上面的qt_signal_spy_callback_set暂时不清楚是什么玩意,所以我们不管,直接看具体的doActive函数- template <bool callbacks_enabled>
- void doActivate(QObject *sender, int signal_index, void **argv)
- {
- // 首先获取QObject的private对象
- QObjectPrivate *sp = QObjectPrivate::get(sender);
- // 判断信号是否阻塞
- if (sp->blockSig)
- return;
- Q_TRACE_SCOPE(QMetaObject_activate, sender, signal_index);
- if (sp->isDeclarativeSignalConnected(signal_index)
- && QAbstractDeclarativeData::signalEmitted) {
- Q_TRACE_SCOPE(QMetaObject_activate_declarative_signal, sender, signal_index);
- QAbstractDeclarativeData::signalEmitted(sp->declarativeData, sender,
- signal_index, argv);
- }
- const QSignalSpyCallbackSet *signal_spy_set = callbacks_enabled ? qt_signal_spy_callback_set.loadAcquire() : nullptr;
- void *empty_argv[] = { nullptr };
- if (!argv)
- argv = empty_argv;
- if (!sp->maybeSignalConnected(signal_index)) {
- // The possible declarative connection is done, and nothing else is connected
- if (callbacks_enabled && signal_spy_set->signal_begin_callback != nullptr)
- signal_spy_set->signal_begin_callback(sender, signal_index, argv);
- if (callbacks_enabled && signal_spy_set->signal_end_callback != nullptr)
- signal_spy_set->signal_end_callback(sender, signal_index);
- return;
- }
- if (callbacks_enabled && signal_spy_set->signal_begin_callback != nullptr)
- signal_spy_set->signal_begin_callback(sender, signal_index, argv);
- bool senderDeleted = false;
- {
- Q_ASSERT(sp->connections.loadAcquire());
- QObjectPrivate::ConnectionDataPointer connections(sp->connections.loadRelaxed());
- QObjectPrivate::SignalVector *signalVector = connections->signalVector.loadRelaxed();
- // 信号连接列表,因为一个信号可能连接了多个槽
- const QObjectPrivate::ConnectionList *list;
- if (signal_index < signalVector->count())
- list = &signalVector->at(signal_index);
- else
- list = &signalVector->at(-1);
- // 判断当前线程是不是信号发送者的线程
- Qt::HANDLE currentThreadId = QThread::currentThreadId();
- bool inSenderThread = currentThreadId == QObjectPrivate::get(sender)->threadData.loadRelaxed()->threadId.loadRelaxed();
- //
- // We need to check against the highest connection id to ensure that signals added
- // during the signal emission are not emitted in this emission.
- uint highestConnectionId = connections->currentConnectionId.loadRelaxed();
- // 此处也就代表着,一个信号连接的多个槽函数,或者多个连接,会以连接的顺序被触发
- do {
- QObjectPrivate::Connection *c = list->first.loadRelaxed();
- if (!c)
- continue;
- do {
- QObject * const receiver = c->receiver.loadRelaxed();
- if (!receiver)
- continue;
- QThreadData *td = c->receiverThreadData.loadRelaxed();
- if (!td)
- continue;
- bool receiverInSameThread;
- // 判断发送和接受是不是同一个线程
- if (inSenderThread) {
- receiverInSameThread = currentThreadId == td->threadId.loadRelaxed();
- } else {
- // need to lock before reading the threadId, because moveToThread() could interfere
- QMutexLocker lock(signalSlotLock(receiver));
- receiverInSameThread = currentThreadId == td->threadId.loadRelaxed();
- }
- // 判断连接方式是否是队列连接,是队列连接就要丢入事件循环队列中处理
- // determine if this connection should be sent immediately or
- // put into the event queue
- if ((c->connectionType == Qt::AutoConnection && !receiverInSameThread)
- || (c->connectionType == Qt::QueuedConnection)) {
- queued_activate(sender, signal_index, c, argv);
- continue;
- #if QT_CONFIG(thread)
- } else if (c->connectionType == Qt::BlockingQueuedConnection) {
- // 如果发送对象和接受对象在一个线程,使用BlockingQueuedConnection会导致死锁
- if (receiverInSameThread) {
- qWarning("Qt: Dead lock detected while activating a BlockingQueuedConnection: "
- "Sender is %s(%p), receiver is %s(%p)",
- sender->metaObject()->className(), sender,
- receiver->metaObject()->className(), receiver);
- }
- QSemaphore semaphore;
- {
- QBasicMutexLocker locker(signalSlotLock(sender));
- if (!c->receiver.loadAcquire())
- continue;
- QMetaCallEvent *ev = c->isSlotObject ?
- new QMetaCallEvent(c->slotObj, sender, signal_index, argv, &semaphore) :
- new QMetaCallEvent(c->method_offset, c->method_relative, c->callFunction,
- sender, signal_index, argv, &semaphore);
- QCoreApplication::postEvent(receiver, ev);
- }
- // 阻塞直至函数执行完成
- semaphore.acquire();
- continue;
- #endif
- }
- // 下面是普通连接,
- // 如果不在一个线程,并且使用直连,那么接收者就为空
- QObjectPrivate::Sender senderData(receiverInSameThread ? receiver : nullptr, sender, signal_index);
- // 如果是槽函数对象
- if (c->isSlotObject) {
- c->slotObj->ref();
- struct Deleter {
- void operator()(QtPrivate::QSlotObjectBase *slot) const {
- if (slot) slot->destroyIfLastRef();
- }
- };
- const std::unique_ptr<QtPrivate::QSlotObjectBase, Deleter> obj{c->slotObj};
- {
- Q_TRACE_SCOPE(QMetaObject_activate_slot_functor, obj.get());
- obj->call(receiver, argv);
- }
- } else if (c->callFunction && c->method_offset <= receiver->metaObject()->methodOffset()) {
- //we compare the vtable to make sure we are not in the destructor of the object.
- const int method_relative = c->method_relative;
- const auto callFunction = c->callFunction;
- const int methodIndex = (Q_HAS_TRACEPOINTS || callbacks_enabled) ? c->method() : 0;
- if (callbacks_enabled && signal_spy_set->slot_begin_callback != nullptr)
- signal_spy_set->slot_begin_callback(receiver, methodIndex, argv);
- {
- Q_TRACE_SCOPE(QMetaObject_activate_slot, receiver, methodIndex);
- callFunction(receiver, QMetaObject::InvokeMetaMethod, method_relative, argv);
- }
- if (callbacks_enabled && signal_spy_set->slot_end_callback != nullptr)
- signal_spy_set->slot_end_callback(receiver, methodIndex);
- } else {
- const int method = c->method_relative + c->method_offset;
- if (callbacks_enabled && signal_spy_set->slot_begin_callback != nullptr) {
- signal_spy_set->slot_begin_callback(receiver, method, argv);
- }
- {
- Q_TRACE_SCOPE(QMetaObject_activate_slot, receiver, method);
- QMetaObject::metacall(receiver, QMetaObject::InvokeMetaMethod, method, argv);
- }
- if (callbacks_enabled && signal_spy_set->slot_end_callback != nullptr)
- signal_spy_set->slot_end_callback(receiver, method);
- }
- // 此处while是循环遍历信号所连接的槽/信号
- } while ((c = c->nextConnectionList.loadRelaxed()) != nullptr && c->id <= highestConnectionId);
- // 循环两次
- } while (list != &signalVector->at(-1) &&
- //start over for all signals;
- ((list = &signalVector->at(-1)), true));
- if (connections->currentConnectionId.loadRelaxed() == 0)
- senderDeleted = true;
- }
- if (!senderDeleted) {
- sp->connections.loadRelaxed()->cleanOrphanedConnections(sender);
- if (callbacks_enabled && signal_spy_set->signal_end_callback != nullptr)
- signal_spy_set->signal_end_callback(sender, signal_index);
- }
- }
复制代码 前面的一些基本的判断,我们就忽略,直接找到重要的地方,循环遍历信号所连接的部分。
- 当信号槽为队列连接,我们需要将信号丢到事件循环里,待事件循环将该信号发送出去。
- if ((c->connectionType == Qt::AutoConnection && !receiverInSameThread)
- || (c->connectionType == Qt::QueuedConnection)) {
- queued_activate(sender, signal_index, c, argv);
- continue;
- #if QT_CONFIG(thread)
- }
复制代码 - 当信号槽为阻塞队列连接(BlockingQueuedConnection)时,首先,我们需要判断发送和接收者是不是在一个线程,因为如果连接类型为BlockingQueuedConnection,发送者和接收者在一个线程,会导致死锁。
- else if (c->connectionType == Qt::BlockingQueuedConnection) {
- // 如果发送对象和接受对象在一个线程,使用BlockingQueuedConnection会导致死锁
- if (receiverInSameThread) {
- qWarning("Qt: Dead lock detected while activating a BlockingQueuedConnection: "
- "Sender is %s(%p), receiver is %s(%p)",
- sender->metaObject()->className(), sender,
- receiver->metaObject()->className(), receiver);
- }
- QSemaphore semaphore;
- {
- QBasicMutexLocker locker(signalSlotLock(sender));
- if (!c->receiver.loadAcquire())
- continue;
- QMetaCallEvent *ev = c->isSlotObject ?
- new QMetaCallEvent(c->slotObj, sender, signal_index, argv, &semaphore) :
- new QMetaCallEvent(c->method_offset, c->method_relative, c->callFunction,
- sender, signal_index, argv, &semaphore);
- QCoreApplication::postEvent(receiver, ev);
- }
- // 阻塞直至函数执行完成
- semaphore.acquire();
- continue;
- #endif
- }
复制代码 其他类型的连接如下:
- 信号的连接是一个槽函数对象QSlotObject,就直接调用call函数
- if (c->isSlotObject) {
- c->slotObj->ref();
- struct Deleter {
- void operator()(QtPrivate::QSlotObjectBase *slot) const {
- if (slot) slot->destroyIfLastRef();
- }
- };
- const std::unique_ptr<QtPrivate::QSlotObjectBase, Deleter> obj{c->slotObj};
- {
- Q_TRACE_SCOPE(QMetaObject_activate_slot_functor, obj.get());
- obj->call(receiver, argv);
- }
- }
复制代码 - 如果是其他类型,就通过QMetaObject::InvokeMetaMethod来调用
- else if (c->callFunction && c->method_offset <= receiver->metaObject()->methodOffset()) {
- //we compare the vtable to make sure we are not in the destructor of the object.
- const int method_relative = c->method_relative;
- const auto callFunction = c->callFunction;
- const int methodIndex = (Q_HAS_TRACEPOINTS || callbacks_enabled) ? c->method() : 0;
- if (callbacks_enabled && signal_spy_set->slot_begin_callback != nullptr)
- signal_spy_set->slot_begin_callback(receiver, methodIndex, argv);
- {
- Q_TRACE_SCOPE(QMetaObject_activate_slot, receiver, methodIndex);
- callFunction(receiver, QMetaObject::InvokeMetaMethod, method_relative, argv);
- }
- if (callbacks_enabled && signal_spy_set->slot_end_callback != nullptr)
- signal_spy_set->slot_end_callback(receiver, methodIndex);
- } else {
- const int method = c->method_relative + c->method_offset;
- if (callbacks_enabled && signal_spy_set->slot_begin_callback != nullptr) {
- signal_spy_set->slot_begin_callback(receiver, method, argv);
- }
- {
- Q_TRACE_SCOPE(QMetaObject_activate_slot, receiver, method);
- QMetaObject::metacall(receiver, QMetaObject::InvokeMetaMethod, method, argv);
- }
- if (callbacks_enabled && signal_spy_set->slot_end_callback != nullptr)
- signal_spy_set->slot_end_callback(receiver, method);
- }
复制代码 并且遍历整个列表,将所有相关的连接都调用一遍。
然后我们看QueuedConnection的连接函数:
代码里,揭示了一点,就是如果我们使用信号槽连接的方式,而信号的参数不是一个元类型或者没用qRegisterMetaType来注册类型,那么队列连接是不行的,槽函数是不会触发的。- static void queued_activate(QObject *sender, int signal, QObjectPrivate::Connection *c, void **argv)
- {
- // 存储元类型参数(meta-type argument)
- const int *argumentTypes = c->argumentTypes.loadRelaxed();
- if (!argumentTypes) {
- // 获取对应的信号
- QMetaMethod m = QMetaObjectPrivate::signal(sender->metaObject(), signal);
- // 获取信号的参数,并检查是否所有参数均为元类型(meta-type)
- argumentTypes = queuedConnectionTypes(m.parameterTypes());
- if (!argumentTypes) // cannot queue arguments
- argumentTypes = &DIRECT_CONNECTION_ONLY;
- if (!c->argumentTypes.testAndSetOrdered(nullptr, argumentTypes)) {
- if (argumentTypes != &DIRECT_CONNECTION_ONLY)
- delete [] argumentTypes;
- argumentTypes = c->argumentTypes.loadRelaxed();
- }
- }
- // 参数不符合要求,返回
- if (argumentTypes == &DIRECT_CONNECTION_ONLY) // cannot activate
- return;
- int nargs = 1; // include return type
- while (argumentTypes[nargs-1])
- ++nargs;
- QBasicMutexLocker locker(signalSlotLock(c->receiver.loadRelaxed()));
- if (!c->receiver.loadRelaxed()) {
- // the connection has been disconnected before we got the lock
- return;
- }
- if (c->isSlotObject)
- c->slotObj->ref();
- locker.unlock();
- // 然后通过post一个QMetaCallEvent事件到事件循环队列中去
- QMetaCallEvent *ev = c->isSlotObject ?
- new QMetaCallEvent(c->slotObj, sender, signal, nargs) :
- new QMetaCallEvent(c->method_offset, c->method_relative, c->callFunction, sender, signal, nargs);
- void **args = ev->args();
- int *types = ev->types();
- types[0] = 0; // return type
- args[0] = nullptr; // return value
- if (nargs > 1) {
- for (int n = 1; n < nargs; ++n)
- types[n] = argumentTypes[n-1];
- for (int n = 1; n < nargs; ++n)
- args[n] = QMetaType::create(types[n], argv[n]);
- }
- locker.relock();
- if (c->isSlotObject)
- c->slotObj->destroyIfLastRef();
- if (!c->receiver.loadRelaxed()) {
- // the connection has been disconnected while we were unlocked
- locker.unlock();
- delete ev;
- return;
- }
- QCoreApplication::postEvent(c->receiver.loadRelaxed(), ev);
- }
复制代码 代码中我们可以看到,这里是通过post一个QMetaCallEvent的事件到事件循环中,然后由事件循环去触发槽函数的调用。
好了,对于信号和槽的分析,我们暂时就先分析到这,如果有问题是我上面没有说明的,可以在评论区给我评论,我看到了,看懂了,我就会更新这篇博客的。
谢谢观看
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