QT 关于使用QThread实现多线程（重写run函数）-蒲公英云

在QT中，有两种多线程的方法，一种是继承QThread的run函数，另一种是把一个继承于QObject的类转移到一个Thread里。

Qt4.8之前都是使用继承QThread的run这种方法（本次主要介绍的就是这种），其主要步骤如下：

0x01、新建一个类（WorkThread），把该类的父类改为QThread

0x02、重写QThread的run函数，在run函数中搞事情（耗时操作）

0x03、在需要使用的地方，new一个子线程，然后调用QThread的 start 方法启动线程。

0x04、如果需要结束线程，则使用QThread的 wait 方法。

示例代码如下（workthread为子线程，maindialog为调用者）：

workthread.h

#ifndef WORKTHREAD_H
#define WORKTHREAD_H
#include <QObject>
#include <QThread>
class WorkThread : public QThread/*QObject*/
{
    Q_OBJECT
public:
    explicit WorkThread(QObject *parent = 0);
signals:
    void currentNum(int);
    void workDone();
public slots:
    void stopThread();
protected:
    virtual void run();
private:
    volatile bool bStop = false;//易失性变量,用volatile进行申明
};
#endif // WORKTHREAD_H

workthread.cpp

#include "workthread.h"
#include <QDebug>
#include <QMessageBox>
WorkThread::WorkThread(QObject *parent) : QThread(parent)
{
}
void WorkThread::run()
{
    //注意:在子线程中不能出现跟UI相关的代码(QMessageBox这些都不行)
    //ASSERT failure in QWidget: "Widgets must be created in the GUI thread.",
    //QMessageBox::information(NULL, "info", "I'm sub thread");
    //do something...
    for(int i=0; i<10; i++)
    {
        if(bStop == false)
        {
            QThread::msleep(500);
            qDebug() << "SubThreadId:" << QThread::currentThreadId() << "i:" << i;
            emit currentNum(i);
        }
    }
    emit workDone();
}
void WorkThread::stopThread()
{
    bStop = true;
}

maindialog.h

#ifndef MAINDIALOG_H
#define MAINDIALOG_H
#include <QDialog>
class MainDialog : public QDialog
{
    Q_OBJECT
public:
    MainDialog(QWidget *parent = 0);
    ~MainDialog();
public slots:
    void onCurrentNum(int);
    void onWorkDone();
};
#endif // MAINDIALOG_H

maindialog.cpp

#include "maindialog.h"
#include "workthread.h"
#include <QPushButton>
#include <QDebug>
MainDialog::MainDialog(QWidget *parent)
    : QDialog(parent)
{
    //创建"开始"按钮 按照控件的大小创建窗口
    QPushButton * btnStart = new QPushButton("Start", this);
    //移动btnStart按钮
    btnStart->move(100,100);
    //调整按钮大小
    btnStart->resize(100,50);
    //创建"停止"按钮 按照控件的大小创建窗口
    QPushButton * btnStop = new QPushButton("Stop", this);
    //移动btnStop按钮
    btnStop->move(300,100);
    //调整按钮大小
    btnStop->resize(100,50);
    //重置窗口大小
    resize(600,400);
    //设置固定窗口大小
    setFixedSize(600,400);
    //设置窗口标题
    setWindowTitle("QThread Test");
    WorkThread *pWork = new WorkThread(this);
    //Qt4版本的写法
//    connect(pWork,SIGNAL(currentNum(int)),this, SLOT(onCurrentNum(int)));
//    connect(pWork,SIGNAL(workDone()),this, SLOT(onWorkDone()));
    //连接带参数的信号和槽(函数指针的写法)
//    void(WorkThread:: *currentNumSigal)(int) = &WorkThread::currentNum;
//    void(MainDialog:: *currentNumSlot)(int)  = &MainDialog::onCurrentNum;
//    connect(pWork, currentNumSigal, this, currentNumSlot);
//    void(WorkThread:: *workDoneSigal)(void) = &WorkThread::workDone;
//    void(MainDialog:: *workDoneSlot)(void)  = &MainDialog::onWorkDone;
//    connect(pWork, workDoneSigal, this, workDoneSlot);
    //Qt5版本写法(Lambda表达式)
    connect(pWork, &WorkThread::currentNum, [=](int val){
        this->onCurrentNum(val);
    });
    connect(pWork, &WorkThread::workDone, [=](){
        this->onWorkDone();
    });
    //关联Start和Stop按钮的信号和槽
    connect(btnStart, &QPushButton::clicked, [=](){
        qDebug() << "MainThreadId:" << QThread::currentThreadId();
        pWork->start();//开启线程
    });
    connect(btnStop, &QPushButton::clicked, [=](){
        pWork->stopThread();
        pWork->wait();//结束线程
    });
}
MainDialog::~MainDialog()
{
}
void MainDialog::onCurrentNum(int num)
{
    qDebug() << "MainDialog::onCurrentNum:" << num;
}
void MainDialog::onWorkDone()
{
    qDebug() << "MainDialog::onWorkDone()";
}

点击Start按钮启动线程后，然后通过stop按钮停止线程，在Qt Creator中应用程序输出：

MainThreadId: 0x2638
SubThreadId: 0x3480 i: 0
MainDialog::onCurrentNum: 0
SubThreadId: 0x3480 i: 1
MainDialog::onCurrentNum: 1
SubThreadId: 0x3480 i: 2
MainDialog::onCurrentNum: 2
SubThreadId: 0x3480 i: 3
MainDialog::onCurrentNum: 3
MainDialog::onWorkDone()