1. testopencvthread.h

//做信号枪
signals:
    void ImageProcessFinished(QImage image);

2. testopencvthread.cpp

//发信号,告诉ImageProcessFinished 我射了
emit ImageProcessFinished(image);

3. mainwindows.h

//做靶子, 注定要给信号枪射的, 逃不掉的, 除非(该函数没在 slots 标志里面)
public slots:
void ShowImageFromThread(QImage image);

4.mainwindows.cpp

//建立轨道, 必须怀孕的轨道
connect(m_pVideoCapture,SIGNAL(ImageProcessFinished(QImage)),
                   this,SLOT(ShowImageFromThread(QImage)));

testopencvthread.h

#ifndef TESTOPENCVTHREAD_H
#define TESTOPENCVTHREAD_H

#include <QWidget>
#include <QThread>
#include <QImage>

#include "opencv2/opencv.hpp"

using namespace cv;

class TestOpencvThread : public QThread
{
    Q_OBJECT
public:
    explicit TestOpencvThread();

public slots:

signals:
    void ImageProcessFinished(QImage image);

protected:
    void run();
    void InitVideoCapture();
private:
    Mat m_srcImage;
    VideoCapture m_videoCap;
};

#endif // TESTOPENCVTHREAD_H

testopencvthread.cpp

#include "testopencvthread.h"
TestOpencvThread::TestOpencvThread() :  QThread()
{
    InitVideoCapture();
}
void TestOpencvThread::InitVideoCapture()
{
    m_videoCap.open(0);
}
void TestOpencvThread::run()
{
    QImage image;
    while(1)
    {
        m_videoCap>>m_srcImage;

        if(m_srcImage.data)
        {
            cvtColor(m_srcImage, m_srcImage, CV_BGR2RGB);//Qt中支持的是RGB图像, OpenCV中支持的是BGR
            image = QImage((uchar*)(m_srcImage.data), m_srcImage.cols, m_srcImage.rows, QImage::Format_RGB888);
        }
        emit ImageProcessFinished(image);
    }
}

mainwindows.h

#include "testopencvthread.h"

class DisplayWidget : public QWidget
{
    Q_OBJECT
public:
    explicit DisplayWidget(QWidget *parent = nullptr);

signals:

public slots:
    void ShowImageFromThread(QImage image);
protected:
    void InitVideoCapture();
private:

    TestOpencvThread *m_pVideoCapture;
    QLabel *m_pxx;
};

#endif // DISPLAYWIDGET_H

mainwundows.cpp

#include "displaywidget.h"

DisplayWidget::DisplayWidget(QWidget *parent) : QWidget(parent)
{
    InitVideoCapture();
    InitLayout();
}
void DisplayWidget::InitVideoCapture()
{
    m_pVideoCapture = new VideoCaptureWidget;
    connect(m_pVideoCapture,SIGNAL(ImageProcessFinished(QImage)),this,SLOT(ShowImageFromThread(QImage)));
    m_pVideoCapture->start();
}
void DisplayWidget::ShowImageFromThread(QImage image)
{
   QPixmap *pixmap = new QPixmap();
   pixmap->scaled(m_pxx->size(), Qt::KeepAspectRatio);
   m_pxx->setPixmap(pixmap->fromImage(image));
}