How to make Qt(PyQt) codes runs in order?

Question

Hello every one. I am making a desktop GUI application using PyQt5 on Windows 7.

In my application, there is a heavy workload. It is making a hash code of all files in specified directories and downloads from ftp if the files hash code is not equal with ftps file. On my system this takes about 5-6 minutes.

In my thought...

show widget first. ( of course, the 'self.show()' is prior to code of compare hash. )
compare hash code and download the files.

Code works properly, but widget show after 2. ends. And this is a problem.
I want to my application runs step 1 first then step 2. What should I do?

Any help is apreciated

Code:

class showUI(QWidget):
  # make menu, toolbar, buttons, etc..
  self.show()

class compareHashAndDownload:
  # compare hash and download the files.

if __name__ == '__main__':
  app = QApplication(sys.argv)
  ex = showUI()
  mainProcess = compareHashAndDownload()
  sys.exit(app.exec_())

You must enter the event loop (app.exec()) to make the widget appear, and not block the event loop while doing the download and computation (do the download asynchronous/event-based or in another thread). — Frank Osterfeld, Nov 30 '15 at 07:06
Thank you, 'Frank Osterfeld'. But I'm not an expert at PyQt. Do you have any example of block/nonblock event loop and how to enter and edit event loop? — passion053, Nov 30 '15 at 07:18
why not just call the `compareHashAndDownload` after the `self.show()` from inside the `showUI` — GIRISH RAMNANI, Nov 30 '15 at 08:32
@GIRISHRAMNANI: That’s equivalent to what he is doing now, I think? — Frank Osterfeld, Nov 30 '15 at 10:11
@GIRISHRAMNANI: Sorry but your solution doesn't make difference... — passion053, Nov 30 '15 at 10:26

score 1 · Accepted Answer · edited May 23 '17 at 11:59

The best way to fix this is to run the compareHashAndDownload in a separate QThread. This would also allow the widget to be interacted with, even before the long running function has completed. You could also re-run the function later and not hang up the GUI in that time.

Using threads is quite complex. For example, you will need to arrange the GUI actions so they operate correctly when called before, during, or after the execution of the compareHashAndDownload function.

There are some nice examples here which will help you if you decide to go down this route.

However, a cheap and cheerful alternative would be to show a splash screen while you perform the compareHashAndDownload. Here's a simple example:

class showUI(QWidget):
  splash = QtGui.QSplashScreen(QtGui.QPixmap(splashFileName))
  splash.show()
  # make menu, toolbar, buttons, etc..
  mainProcess = compareHashAndDownload()
  self.show()
  splash.finish(self)

class compareHashAndDownload:
  # compare hash and download the files.

if __name__ == '__main__':
  app = QApplication(sys.argv)
  ex = showUI()

  sys.exit(app.exec_())

Thank yo very much 'strubbly'. You showed me a right way and good workaround! thank you again! — passion053, Nov 30 '15 at 14:41

score 0 · Answer 2 · answered Nov 30 '15 at 08:39

you can directly call compareHashAndDownload from the showUI widget itself. But if your compare method takes too long then the ui will wait from it to complete and thats not a nice experience.So keep that in mind.

class showUI(QWidget):
  # make menu, toolbar, buttons, etc..
  mainProcess = compareHashAndDownload()
  self.show()

class compareHashAndDownload:
  # compare hash and download the files.

if __name__ == '__main__':
  app = QApplication(sys.argv)
  ex = showUI()

  sys.exit(app.exec_())

this will work fine is the method doesnt take that long, if it does then use qt's own QThread to run the method on seperate thread (not the most elegant solution but will work fine) .

As I mentioned, My code has heavy workload(5, 6minutes). So your solution makes no difference. I need the way to completely show the ui first. Your code result same as I write.... — passion053, Nov 30 '15 at 10:01

How to make Qt(PyQt) codes runs in order?

2 Answers2