[PySide] a couple of QProgressDialog questions

Sebastian Elsner sebastian at risefx.com
Sat Sep 7 08:37:04 CEST 2013

Looks pretty good! I totally forgot that QProcess is asynchronous so you
can save the thread

The only thing I dont like is :

from PySide.QtCore import *
from PySide.QtGui import *

which is not recommended, because it will pollute your namespace with
stuff you might not know about - overwriting functions with unexpected

For the "100% not emitted" problem: just connect the QProcess.finished
signal to your __read method. The doc says the buffers are still intact
after this signal is emitted and you are able to read from stdout and
get the 100% done line.

Am 07.09.2013 07:44, schrieb Frank Rueter | OHUfx:
> Here is what I got:
> http://pastebin.com/kCUkSsUX
> I didn't even need QThread at all since QProcess seems to be taking care 
> of everything as expected.
> It's working nicely, though I had a few times where the last signal of 
> 100% wasn't emitted for some reason.
> Does this look about right?
> Cheers and thanks again for the help!
> frank
> On 3/09/13 8:01 PM, Sebastian Elsner wrote:
>> On 09/03/2013 08:31 AM, Frank Rueter | OHUfx wrote:
>>> Hi everybody,
>>> after almost a year of having to neglect PySide I'm finally making some
>>> time for it again, only to feel like I almost forgot everything I
>>> learned :-D
>>> I'm trying to do something fairly common and wanted to sanity check my
>>> approach, so here is my sandbox script to figure out how to use
>>> QProgressDialog:
>>> http://pastebin.com/4kVhPiUx
>>> It all works as expected except for the fact that when I hit cancel, the
>>> progress stops (as expected), and the second time I hit the cancel
>>> button the dialog closes. Seems wrong, and I'm sure I should be doing it
>>> better, so that the progress stops and the dialog closes at the same
>>> time. This behaviour seems to be the same even if setAutoClose() is set
>>> to True.
>> auto close only works if the current progress value is equal with the
>> maximum value.
>>> Should manually close the window when wasCanceled() is true, or set the
>>> progress' value to it's maximum to let auroClose take over? Or is there
>>> a better way?
>> I normally do dlg.setValue(dlg.maximum()) and let autoclose do the rest,
>> because afaik it also takes care of resetting stuff
>>> My second question is:
>>> What is the best approach to connect a QProgressDialog to another thread
>>> that is running a command line application?
>>> I'm guessing I should write a wrapper around the external application
>>> (using QEvent or QProcess?), grabbing it's stdout, parsing it to get the
>>> actual progress value, then connecting that to the QProgressDialog widget.
>>> Is that the way to do it?
>> Thats basically it. Your example suggests, that you want to put the
>> computation code in the QProgressDialog subclass - don't. This is how
>> the pieces should work together:
>> Create a subclass of QObject. This is your object, that launches the
>> QProgress and runs in its own thread watching and parsing the output of
>> the QProgress. This class communicates ONLY via signals and slots with
>> the main thread (normal method calls to the QProgress/within the thread
>> are OK). This means you need a signal, which signals what the current
>> progress is. Do not follow the old QThread documentation it is WRONG :)
>> Read up on this topic here:
>> http://blog.qt.digia.com/blog/2010/06/17/youre-doing-it-wrong/ and get a
>> recent 4.8.4 documentation. Move this QObject to a QThread instance and
>> connect the usual signals according to the docs. Create a
>> QProgressDialog, connecting the canceled signal to a slot in your
>> QObject to signal to stop the computation. Connect the progress signal
>> from the QObject to the setValue of your progress dialog. For this to
>> work you do only need to subclass QObject.
>>> Ultimately I would like a simple Dialog, that has both a progress bar
>>> and a text widget, to show the application's stdout as well as the
>>> overall progress.
>> Thats totally possible, just fire up qtdesigner and put it together.
>> As an exercise you could try to de-couple this new dialog totally from
>> the actual type of command line program it is running by providing a way
>> to generally configure the command line to run and a regex to parse the
>> stdout for progress.
>>> Am I on the right track or are there easier/better ways?
>>> Cheers,
>>> frank
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