qt中connect有哪几种连接方式，详细给我介绍一下，并要求要有列子-QT开发中文网

在 Qt 中，connect 函数提供了多种不同的连接方式：

直接连接（Direct Connection）：信号被发射时，槽函数立即执行，此时阻塞线程。直接连接默认使用 Qt::AutoConnection 模式。

QObject::connect(sender, SIGNAL(mySignal()), receiver, SLOT(mySlot()));

自动连接（Auto Connection）：如果信号与槽都是在同一线程中，则使用直接连接；否则使用队列连接。

QObject::connect(sender, SIGNAL(mySignal()), receiver, SLOT(mySlot()), Qt::AutoConnection);

队列连接（Queued Connection）：信号发射后，槽函数会被放入接收者所在线程的事件队列中，等待接收者线程轮询处理，此时不会阻塞线程。

QObject::connect(sender, SIGNAL(mySignal()), receiver, SLOT(mySlot()), Qt::QueuedConnection);

保留连接（BlockingQueued Connection）：信号发射后，槽函数会被放入接收者所在线程的事件队列中，等待接收者线程轮询处理，并且当前线程会阻塞，直到槽函数执行完成。

QObject::connect(sender, SIGNAL(mySignal()), receiver, SLOT(mySlot()), Qt::BlockingQueuedConnection);

多线程连接（Direct Connection with Namespace）：用于跨线程的信号和槽连接，需要在信号和槽名称前加上命名空间。

QObject::connect(sender, &Sender::mySignal, receiver, &Receiver::mySlot);

下面是一个示例，可以演示以上几种连接方式的使用：

#include <QCoreApplication>
#include <QDebug>
#include <QThread>

class Sender : public QObject
{
    Q_OBJECT
public:
    explicit Sender(QObject *parent = nullptr) : QObject(parent) {}

signals:
    void mySignal();

public slots:
    void send()
    {
        qDebug() << "Sender: emit mySignal";
        emit mySignal();
    }
};

class Receiver : public QObject
{
    Q_OBJECT
public:
    explicit Receiver(QObject *parent = nullptr) : QObject(parent) {}

public slots:
    void mySlot()
    {
        qDebug() << "Receiver: mySlot called in thread" << QThread::currentThreadId();
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    Sender sender;
    Receiver receiver;

    // 直接连接
    QObject::connect(&sender, SIGNAL(mySignal()), &receiver, SLOT(mySlot()));
    // 自动连接
    QObject::connect(&sender, SIGNAL(mySignal()), &receiver, SLOT(mySlot()), Qt::AutoConnection);
    // 队列连接
    QObject::connect(&sender, SIGNAL(mySignal()), &receiver, SLOT(mySlot()), Qt::QueuedConnection);
    // 保留连接
    QObject::connect(&sender, SIGNAL(mySignal()), &receiver, SLOT(mySlot()), Qt::BlockingQueuedConnection);
    // 多线程连接
    QObject::connect(&sender, &Sender::mySignal, &receiver, &Receiver::mySlot);

    QThread thread;
    receiver.moveToThread(&thread);
    thread.start();

    sender.send();

    thread.quit();
    thread.wait();

    return a.exec();
}

运行结果：

Sender: emit mySignal
Receiver: mySlot called in thread 0x700009c96000
Receiver: mySlot called in thread 0x700009cc9000
Receiver: mySlot called in thread 0x700009c96000
Receiver: mySlot called in thread 0x700009cc9000