I have a need to update a QProgressBar while a slider is begin dragged, without
processing user events.
.
I tried calling QProgressBar.repaint(), as shown in the sample code below. This
works fine for linux/X11 (and osx/X11), but for osx/aqua I never see the
progress bar change. It seems that repaint() under osx has no effect. I'm
guessing that it causes drawing to occur to the off screen buffer, but never
copies that to the main screen.
I tried calling QApplication.processEvents(QEventLoop.ExcludeUserInputEvents)
instead of QProgressBar.update(). That makes the progress bar update correctly,
but I end up with funny slider movements where it jiggles back and forth a bit
instead of exactly tracking the mouse, and weird focus issues where the next
few mouse clicks after the last call to
QApplication.processEvents(QEventLoop.ExcludeUserInputEvents) get sent to the
wrong widget.
In case anyone is wondering why I need to do this...
My app does data visualization, and I have a slider that makes some adjustments
to my display widget. Most of the time the adjustment occurs near
instantaneously, so that the user sees the display update in real time as they
drag the slider. But occasionally, depending on the nature of the data, the
adjustment to the display widget can take up to 10 seconds. So when the
adjustment takes a long time I need some way to inform the user that the app is
processing their request (and hasn't hung) and give an estimate of how long its
going to take for the screen to update. If I allow normal event handling while
the adjustment to the widget is begin made (by calling processEvents() or
running the adjustment in a separate thread) then the adjustment of the display
widget would lag way behind the slider movement, and the user would have the
ability to trigger some other operation on the display widget during the
adjustment, which would lead to corruption of data in the widget.
Does anyone have any suggestions on how to get the same progress bar update
behavior I see under X11 to occur under osx/aqua?
Thanks
- J
from PyQt4 import QtGui
from PyQt4.QtCore import Qt
import time
import sys
class TestWindow(QtGui.QWidget):
def __init__(self):
QtGui.QWidget.__init__(self)
l = QtGui.QVBoxLayout()
slider = QtGui.QSlider(Qt.Horizontal, self)
slider.setRange(0,100)
l.addWidget(slider)
self.pb = QtGui.QProgressBar(self)
self.pb.setRange(0,20)
l.addWidget(self.pb)
self.setLayout(l)
slider.valueChanged.connect(self.doStuff)
def doStuff(self, v):
for i in xrange(20):
self.pb.setValue(i)
self.pb.repaint()
time.sleep(0.05)
self.pb.reset()
app = QtGui.QApplication(sys.argv)
w = TestWindow()
w.show()
app.exec_()
Jason Ferrara
Jacquette Consulting, Inc.
710 Providence Road
Malvern, PA 19355
[email protected]
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