PyQt4：不能从另一个线程启动计时器

Question

When I run the following code ...

import sys, time
from PyQt4 import QtCore, QtGui

class WorkThread(QtCore.QThread):
 def __init__(self):
  QtCore.QThread.__init__(self)

 def run(self):
  for i in range(100):
   time.sleep(1) # artificial time delay
   print(i)
   test.pbar.setValue(i)
  return


class MyApp(QtGui.QWidget):
 def __init__(self):
  QtGui.QWidget.__init__(self, None)
  self.setGeometry(300, 300, 280, 600)
  self.setWindowTitle('threads')
  self.layout = QtGui.QVBoxLayout(self)
  self.pbar = QtGui.QProgressBar(self)
  self.layout.addWidget(self.pbar)



# run
app = QtGui.QApplication(sys.argv)
test = MyApp()
workThread = WorkThread()
workThread.start()
test.show()
app.exec_()

I get the following error ...

QObject::startTimer: timers cannot be started from another thread

The code still continues to execute ok, but what I dont understand is why this error stops appearing after I remove test.pbar.setValue(i) OR replace pbar with a different widget such as a list. It seems obvious that the error is specific to the progressbar widget ...

Answer 1

As I mentioned in my comment, the error you're seeing provides you exactly with the information it was meant to provide. You are not allowed to invoke QObject::setTimer from a thread different from the one in which the timer was created. Specifically, one version of the code of QObject I found has this code:

int QObject::startTimer(int interval)
{
    Q_D(QObject);

    if (interval < 0) {
        qWarning("QObject::startTimer: QTimer cannot have a negative interval");
        return 0;
    }

    d->pendTimer = true;                                // set timer flag

    if (!d->threadData->eventDispatcher) {
        qWarning("QObject::startTimer: QTimer can only be used with threads started with QThread");
        return 0;
    }
    return d->threadData->eventDispatcher->registerTimer(interval, this);
}

Note the warning-generating code.

Calling the pbar.setValue method obviously makes a call to this startTimer method, which creates the warning.

Now, I'm not sure what your problem with this is? Do you absolutely need to control the progress bar directly from another thread? That's not a good idea.