Qt实现多线程编程的两种方式

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方式一： 继承自QThread类，覆写run函数。此实现方法只有run函数内的代码是运行在子线程内。

代码示例：

#ifndef QDEMOTHREAD_H
#define QDEMOTHREAD_H#include <QThread>
#include <QDebug>class QDemoThread : public QThread
{Q_OBJECTpublic:QDemoThread(QObject* parent = nullptr);~QDemoThread();protected:void run() override;public:void stop();private:bool flag;
};#endif // QDEMOTHREAD_H

#include "qdemothread.h"QDemoThread::QDemoThread(QObject* parent) : QThread(parent)
{}QDemoThread::~QDemoThread()
{}void QDemoThread::run()
{flag = true;while(flag){qDebug() << "thread id:" << QThread::currentThreadId();sleep(1);}
}void QDemoThread::stop()
{flag = false;if(isRunning()){exit();  // 结束线程wait();  // 等待退出}
}

#include "widget.h"
#include "ui_widget.h"Widget::Widget(QWidget *parent) :QWidget(parent),ui(new Ui::Widget)
{ui->setupUi(this);demoThread = new QDemoThread(this);qDebug() << "main thread id:" << QThread::currentThreadId();
}Widget::~Widget()
{demoThread->stop();  // 退出线程delete ui;
}void Widget::on_pushButton_clicked()
{if(!demoThread->isRunning()){demoThread->start();  // 启动线程}
}

运行效果：

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方式二： 创建一个QThread和QWorker(继承自QObject)类对象，使用moveToThread函数移动到thread中运行，通过thread类start信号和worker的init槽函数绑定，init槽函数内是一些初始化操作，然后定义个定时器，周期触发doWork()。

网上有很多教程是在doWork()中使用while(isRunning)死循环的形式，不建议这么干，如果线程一直在doWork中死循环，那么他是无法接收到来自外部的信号的。推荐的方法是用定时器周期触发。

示例代码：

QWorker类：

#ifndef QWORKER_H
#define QWORKER_H#include <QObject>
#include <QThread>
#include <QDebug>class QWorker : public QObject
{Q_OBJECT
public:explicit QWorker(QObject *parent = nullptr);~QWorker();signals:void newData(QByteArray data);    // 将本类内的私有数据通过该信号发射出去，供外部使用public slots:void init();         // 一些必要的初始化操作写在此函数内void doWork();       // 一些耗时操作写在此函数内void writeData(const char* buf, qint64 len);  // 供外部使用的操作接口
};#endif // QWORKER_H

#include "qworker.h"QWorker::QWorker(QObject *parent) : QObject(parent)
{qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();
}QWorker::~QWorker()
{qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();
}void QWorker::init()
{qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();
}void QWorker::doWork()
{static int count = 0;qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId() << ">>>" << count++;
}void QWorker::writeData(const char* buf, qint64 len)
{qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId() << ">>>" << QByteArray(buf, len);
}

主线程：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H#include <QMainWindow>
#include "qworker.h"
#include <QTimer>namespace Ui {
class MainWindow;
}class MainWindow : public QMainWindow
{Q_OBJECTpublic:explicit MainWindow(QWidget *parent = 0);~MainWindow();private slots:void on_pushButton_clicked();private:Ui::MainWindow *ui;QWorker* worker;QThread* thread;QTimer* timer;signals:void writeData(const char* buf, qint64 len);void stopWork();
};#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"MainWindow::MainWindow(QWidget *parent) :QMainWindow(parent),ui(new Ui::MainWindow)
{ui->setupUi(this);qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();timer = new QTimer(this);thread = new QThread();  // 不要指定parentworker = new QWorker();  // 不要指定parent// thread的finished和deleteLater相连接后，在thread退出时自动删除thread对象，无需手动delete threadconnect(thread, SIGNAL(finished()), thread, SLOT(deleteLater())); // thread的finished和worker的deleteLater相连接后，在thread退出时自动删除worker对象，无需手动delete workerconnect(thread, SIGNAL(finished()), worker, SLOT(deleteLater()));connect(thread, SIGNAL(started()), worker, SLOT(init()));connect(timer, SIGNAL(timeout()), worker, SLOT(doWork()));connect(this, SIGNAL(writeData(const char*,qint64)), worker, SLOT(writeData(const char*,qint64)));worker->moveToThread(thread);thread->start();timer->start(1000);  // 1000ms执行一次doWork()
}MainWindow::~MainWindow()
{if(timer->isActive()){timer->stop();}if(thread->isRunning()){thread->quit();thread->wait();}qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();delete ui;
}void MainWindow::on_pushButton_clicked()
{emit writeData("hello world\r\n", 13);
}

程序界面：

运行后控制台打印信息如下：

可以看到的是，MainWindow和QWorker的构造函数中都显示线程ID为0x336c，而在QWorker的析构函数中显示线程ID为0x22a8，这说明moveToThread确实将worker移动到了thread中；而且还可以看到的是，QWorker的槽函数init、doWork、writeData也都是运行在了子线程中！

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