定义两个类：Receiver接收信号，等待2秒后执行。Sender发送信号触发Receiver槽函数的执行
class Receiver : public QObject {
Q_OBJECT
public slots:
void exec() {
QThread::sleep(1);
qDebug() << QThread::currentThreadId() << "receiver exec";
}
};
class Sender : public QObject {
Q_OBJECT
public:
void exec() {
emit sig();
qDebug() << QThread::currentThreadId() << "sender exec";
}
signals:
void sig();
};
1. moveToThread()，但是直接调用
将sender对象放入线程，但是显示调用sender对象的exec()方法，此时moveToThread不起作用，receiver和sender都在主线程中执行，sender发送信号时，会等待receiver的槽函数执行完毕才执行后续的输出
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
Receiver* r = new Receiver();
Sender* s = new Sender();
QObject::connect(s, SIGNAL(sig()), r, SLOT(exec()));
QThread* thread = new QThread();
s->moveToThread(thread);
thread->start();
s->exec();
QThread::sleep(1000);
return a.exec();
}
2. 槽函数在子线程中执行
将receiver放到单独的线程中，sender在主线程中发信号触发receiver的槽函数。此时默认槽函数连接方式Qt::AutoConnection等同于Qt::QueuedConnection，槽函数在子线程中执行，sender发送信号后立刻执行输出语句
额外的：
- 子线程必须通过start()开启，否则receiver
- 如果指定槽函数的连接方式为Qt::DirectConnection，槽函数也会在主线程中执行
int main() {
Receiver* r = new Receiver();
Sender* s = new Sender();
QObject::connect(s, SIGNAL(sig()), r, SLOT(exec()));
QThread* thread = new QThread();
r->moveToThread(thread);
thread->start();
s->exec();
QThread::sleep(1000);
}
3. 信号循环发送，但槽函数执行速度慢
将Sender类的exec()函数改为循环执行5次，发送5次信号会直接执行完成。Receiver中的槽函数正常执行5次，执行过程不会被新来的信号打断
class Sender : public QObject {
Q_OBJECT
public:
void exec() {
for (int i = 0; i < 5; i++) {
emit sig();
qDebug() << QThread::currentThreadId() << "sender exec";
}
}
signals:
void sig();
};
4. 一次触发两个槽函数
Sender中一次发送两个信号，分别触发Receiver中的两个槽函数，一个延迟1s执行一个立即执行。槽函数按照发送信号的顺序执行。
class Sender : public QObject {
Q_OBJECT
public:
void exec() {
for (int i = 0; i < 5; i++) {
emit sig();
emit sig2();
qDebug() << QThread::currentThreadId() << "sender exec";
}
}
signals:
void sig();
void sig2();
};
class Receiver : public QObject {
Q_OBJECT
public slots:
void exec() {
QThread::sleep(1);
qDebug() << QDateTime::currentDateTime() << QThread::currentThreadId() << "receiver exec";
}
void exec2() {
qDebug() << QDateTime::currentDateTime() << QThread::currentThreadId() << "receiver exec2";
}
};
总结： 在Qt::QueuedConnection连接模式下，跨线程的槽函数调用会按照信号发送顺序执行。槽函数执行过程中不会被中断，槽函数执行完毕后再次开始事件循环，继续执行下一次的槽函数。来不及执行的信号和参数会被框架“保存”起来
