不能发出QThread信号

Question

QT 5.1.0rc2，msvc 2010,2010

它是Qt 4.8.4，msvc 2008上的工作代码

我的编译错误在

#if defined( HANDLE_PROCESSING_IN_MAIN_THREAD )
    if(QThread::currentThread() != this)
        emit started();
#endif
    inherited::run();

和

#if defined( HANDLE_PROCESSING_IN_MAIN_THREAD )
    if(QThread::currentThread() != this)
      emit finished();
#endif

错误C2660：'QThread::started‘：function不接受0参数 错误C2660：'QThread::finished‘：function不接受0参数

我在QThread上见过

Q_SIGNALS:
    void started(
#if !defined(Q_QDOC)
      QPrivateSignal
#endif
    );
    void finished(
#if !defined(Q_QDOC)
      QPrivateSignal
#endif
    );

当我定义Q_QDOC时，我在QT源代码中得到了许多错误。

QPrivateSignal是在宏Q_OBJECT中定义的空结构。

需要不影响应用程序体系结构的解决方案，如向后兼容Qt4.8.4

一些想法？

Answer 1

线程的信号会自动发出。你不应该手动发射它们。

您正在尝试使用预处理器来处理代码的两个变体: gui线程中的处理或专用线程中的处理。Qt提供了一种非常简单的处理方法。

1. 在派生自QObject的类中的槽中实现处理功能。如果通过投递事件而不是调用插槽来开始处理，您也可以在重新实现的event()方法中这样做。
2. 如果希望在不同的线程中运行对象的槽，请使用moveToThread()方法。
3. 您不需要从QThread派生。它的默认run()实现会旋转一个本地事件循环。
4. 如果您希望您的对象与GUI线程中的对象兼容，那么它必须以小块的形式进行处理，并放弃控制，这样GUI就不会停止。

下面是一个完整的示例，演示如何在GUI或单独线程中启动worker对象，以及如何在线程之间安全地移动它。

// https://github.com/KubaO/stackoverflown/tree/master/questions/qobject-thread-18653347
#include <QtGui>
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
#include <QtWidgets>
#endif

/// See http://stackoverflow.com/a/40382821/1329652
bool isSafe(QObject * obj) {
   Q_ASSERT(obj->thread() || qApp && qApp->thread() == QThread::currentThread());
   auto thread = obj->thread() ? obj->thread() : qApp->thread();
   return thread == QThread::currentThread();
}

class Helper : private QThread {
public:
   using QThread::usleep;
};

class Worker : public QObject {
   Q_OBJECT
   int m_counter;
   QBasicTimer m_timer;
   void timerEvent(QTimerEvent * ev) override;
public:
   Worker(QObject *parent = nullptr) : QObject(parent) {}
   /// This method is thread-safe.
   Q_SLOT void start() {
      if (!isSafe(this)) return (void)QMetaObject::invokeMethod(this, "start");
      if (m_timer.isActive()) return;
      m_counter = 0;
      m_timer.start(0, this);
   }
   /// This method is thread-safe.
   Q_INVOKABLE void startInThread(QObject *targetThread) {
      if (!isSafe(this)) return (void)QMetaObject::invokeMethod(this, "startInThread", Q_ARG(QObject*, targetThread));
      QObject::moveToThread(qobject_cast<QThread*>(targetThread));
      start();
   }
   Q_SIGNAL void done();
   Q_SIGNAL void progress(int percent, bool inGuiThread);
};

void Worker::timerEvent(QTimerEvent * ev)
{
   const int busyTime = 50; // [ms] - longest amount of time to stay busy
   const int testFactor = 128; // number of iterations between time tests
   const int maxCounter = 30000;
   if (ev->timerId() != m_timer.timerId()) return;

   const auto inGuiThread = []{ return QThread::currentThread() == qApp->thread(); };
   QElapsedTimer t;
   t.start();
   while (1) {
      // do some "work"
      Helper::usleep(100);
      m_counter ++;
      // exit when the work is done
      if (m_counter > maxCounter) {
         emit progress(100, inGuiThread());
         emit done();
         m_timer.stop();
         break;
      }
      // exit when we're done with a timed "chunk" of work
      // Note: QElapsedTimer::elapsed() may be expensive, so we call it once every testFactor iterations
      if ((m_counter % testFactor) == 0 && t.elapsed() > busyTime) {
         emit progress(m_counter*100/maxCounter, inGuiThread());
         break;
      }
   }
}

class Window : public QWidget {
   Q_OBJECT
   QVBoxLayout m_layout{this};
   QPushButton m_startGUI{"Start in GUI Thread"};
   QPushButton m_startWorker{"Start in Worker Thread"};
   QLabel m_label;
   QThread m_thread{this};
   Worker m_worker;

   Q_SLOT void showProgress(int p, bool inGuiThread) {
      m_label.setText(QString("%1 % in %2 thread")
                      .arg(p).arg(inGuiThread ? "gui" : "worker"));
   }
   Q_SLOT void on_startGUI_clicked() {
      m_worker.startInThread(qApp->thread());
   }
   Q_SLOT void on_startWorker_clicked() {
      m_worker.startInThread(&m_thread);
   }
public:
   Window(QWidget *parent = {}, Qt::WindowFlags f = {}) : QWidget(parent, f) {
      m_layout.addWidget(&m_startGUI);
      m_layout.addWidget(&m_startWorker);
      m_layout.addWidget(&m_label);
      m_thread.start();
      connect(&m_worker, SIGNAL(progress(int,bool)), SLOT(showProgress(int,bool)));
      connect(&m_startGUI, SIGNAL(clicked(bool)), SLOT(on_startGUI_clicked()));
      connect(&m_startWorker, SIGNAL(clicked(bool)), SLOT(on_startWorker_clicked()));
   }
   ~Window() {
      m_thread.quit();
      m_thread.wait();
   }
};

int main(int argc, char *argv[])
{
   QApplication a(argc, argv);
   Window w;
   w.show();
   return a.exec();
}

#include "main.moc"