在Qt中正确的线程方式 [英] Correct way of threading in Qt

问题描述

我有时间的图像加载（图像是大），还有一些操作上就完成了加载。我不想阻止应用程序GUI。

I have time consuming image loading (image is big), also some operations on it are done when loading. I do not want to block application GUI.

我的想法是在另一个线程中加载图片，发出加载图片的信号，然后使用此图片重绘视图。

My idea is to load image in another thread, emit signal that image is loaded and then redraw view with this image.

我的方法：

void Window::loadImage()
{ 
    ImageLoader* loaderThread = new ImageLoader();
    connect(loaderThread,SIGNAL(imageLoaded()),this,SLOT(imageLoadingFinished());
    loaderThread->loadImage(m_image, m_imagesContainer, m_path);
}
void Window::imageLoadingFinished()
{
    m_imagesContainer->addImage(m_image);
    redrawView();
}

class ImageLoader : public QThread
{
    Q_OBJECT
    public:
       ImageLoader(QObject *parent = 0) : m_image(NULL), m_container(NULL)

       void loadImage(Image* img, Container* cont, std::string path)
       {
            m_image = img;
            m_container = cont;
            ...
            start();
       }
    signals:
       void imageLoaded();
    protected:
       void run()
       {
           //loading image and operations on it
           emit imageLoaded();
       }
    protected:
       Image* m_image;
       Container* m_container;
}

我基于 quedcustomtype 示例从Qt写这个代码。当在stackoverflow中进行搜索和搜索时，我还发现子类化 QThread 不是一个好主意。

I was basing on quedcustomtype example from Qt writing this code. When googling and searching in stackoverflow I've also find out that subclassing QThread is not a good idea.

所以问题是什么是正确的方法呢？正如我所说，我想要非阻塞的GUI，加载和操作完成在另一个线程和信号，说加载完成。在信号被发出后，视图应该被重绘。
我不知道多线程，但是认为理解或有足够的知识来理解基本的想法。

So the question is what is the correct way to do it? As I said I want non blocking GUI, loading and operations done in another thread and signal which says loading is finished. After signal is emited view should be redrawn. I don't know much about multithreading however think to understand or have sufficient knowledge to understand basic ideas.

推荐答案

我想这是最好的方式：

#include <QApplication>
#include <QLabel>
#include <QThread>

class ImageLoader : public QObject
{
   Q_OBJECT
public:
   ImageLoader() : QObject() {
      moveToThread(&t);
      t.start();
   }
   ~ImageLoader() {
      qDebug("Bye bye!");
      t.quit();
      t.wait();
   }

   void requestImage(QString absPath) {
      QMetaObject::invokeMethod(this, "loadImage", Q_ARG(QString, absPath));
   }

public slots:
   void loadImage(QString absPath) {
      // Simulate large image.
      QImage image(absPath);
      sleep(10);
      qDebug("Image loaded!");
      emit imageReady(image);
   }

signals:
   void imageReady(QImage image);

private:
   QThread t;
};

class MyLabel : public QLabel
{
   Q_OBJECT
public:
   MyLabel() : QLabel() {}

   void mousePressEvent(QMouseEvent* ev) {
      Q_UNUSED(ev);
      qDebug("I got the event!");
   }

public slots:
   void setImage(QImage image) {
      setPixmap(QPixmap::fromImage(image));
      resize(image.width(), image.height());
      qDebug("Image shown!");
   }
};

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

   MyLabel label;
   label.show();

   ImageLoader imageLoader;
   QObject::connect(&imageLoader, SIGNAL(imageReady(QImage)), &label, SLOT(setImage(QImage)));
   imageLoader.requestImage(some_abs_path);

   return a.exec();
}

#include "main.moc"

也喜欢QtConcurrent，但认为它的使用在某种程度上被劝阻： http： //www.mail-archive.com/[e-mail]/msg07794.html 。

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