the following sample code is crashing with this error when I close the application:
QBasicTimer::start: QBasicTimer can only be used with threads started with QThread
here is my code :
import sys
from PyQt4 import QtGui ,QtCore
app = QtGui.QApplication(sys.argv)
data=[]
data.append("one")
model=QtGui.QStringListModel(data)
combobox=QtGui.QComboBox()
combobox.show()
combobox.setModel(model)
sys.exit(app.exec_())
I found out that's about using model but I don't know how to fix it.
edited:
os : win 7 64bit
pyqt4
The program is not "crashing": it is merely printing an error message during the normal shutdown process.
The reason the message is being shown is a side-effect of garbage-collection. When python shuts down, the order in which objects get deleted can be unpredictable. This may result in objects on the C++ side being deleted in the "wrong" order, and so Qt will sometimes complain when this happens.
One way to "fix" the sample code would be to simply rename some of the PyQt objects. If I change the name combobox to combo, for instance, the error message goes away. There's nothing mysterious about this - it just changes the order in which the objects are deleted.
But another, much more robust, way to fix the problem would be to make sure the QStringListModel has a parent, since it's possible that Qt doesn't take ownership of it when it's passed to the combo-box. Qt should always handle the deletion of child objects correctly when they're linked together in this way. So the code example would become:
import sys
from PyQt4 import QtGui, QtCore
app = QtGui.QApplication(sys.argv)
combobox = QtGui.QComboBox()
data = []
data.append("one")
model = QtGui.QStringListModel(data, combobox)
combobox.setModel(model)
combobox.show()
sys.exit(app.exec_())
Related
My problem is that I have a file with my UI called xxx.ui. Then as many have suggested I created another python file called test.py where I have put code to use my xxx.ui:
# imports
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5 import uic
import sys
class Ui(QtWidgets.QMainWindow):
def __init__(self):
super(Ui, self).__init__()
uic.loadUi('xxx.ui', self)
self.show()
app = QtWidgets.QApplication(sys.argv)
window = Ui()
app.exec_()
Up until this stage everything works ok. But now I would like to add a checkbox to my UI whe program starts without messing inside xxx.ui (so the checkbox will be created dynamicaly when the program runs).
How can I do that ???
Thank You in advance.
After many fail attempts I have found how to do it:
To add Checkbox outside of xxx.ui file. I went to my test.py file and added code below this line:
uic.loadUi('xxx.ui', self)
The code looks like that (I am using horizontal layout widget created in designer called seasonLayout and my checkbox is inside that layout):
self.checkBox = QtWidgets.QCheckBox(self.horizontalLayoutWidget)
self.checkBox.setObjectName("checkBox_0")
self.checkBox.setText('Hello')
self.seasonLayout.addWidget(self.checkBox)
Then if You want to get to that object all You have to do is to use code below:
(here i change text of this newly created checkbox):
self.checkBoxs = self.findChild(QtWidgets.QCheckBox, 'checkBox_0')
self.checkBoxs.setText('test')
Hopefuly it will be helpful for other because I have really tried to find answer for that almost everywhere and everyone were just using widgets from designer - noone explain how to add them outside of it.
This question already has answers here:
QtDesigner changes will be lost after redesign User Interface
(2 answers)
Closed 4 years ago.
I've been looking for a better way to work with frontends made using qtDesigner connected to a python backend. All the methods I have found have the following form:
Make GUI in designer
Output to python code using pyuic (usually with -x option)
Write backend code inside this output file
This methodology is not simple to maintain or edit. Any time you change the UI, it completely breaks workflow: you have to reconvert, generate a new file, fix that file back up to where you were before, then finally get back on track. This requires a lot of manual copy-paste of code, which is an invitation to errors on multiple levels (newly generated file layout may not be the same, manually fixing name changes while pasting, etc.). You can also end up losing work if you aren't careful, since you could accidentally overwrite the file and destroy the backend code.
Also, this doesn't use any of the control in qtDesigner like the Signal/Slot and Action editors. These must be here for something, but I can't find a way to actually direct these to call backend functions.
Is there a better way to work with this, possibly using the features of qtDesigner?
You don't have to add your code in the output file :
If you take a 'home.py' generated by PYUIC, containing a QMainWindow which name set by QtDesigner/generated by Puic would be Ui_Home(), your main code could be :
from home import Ui_Home
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
class window_home(QMainWindow):
def __init__(self, parent=None):
QMainWindow.__init__(self, parent)
#set up the user interface from Designer
self.ui = Ui_Home()
self.ui.setupUi(parent)
#then do anything as if you were in your output file, for example setting an image for a QLabel named "label" (using QtDesigner) at the root QMainWindow :
self.ui.label.setPixmap(QPixmap("./pictures/log.png"))
def Home():
f=QMainWindow()
c=window_home(f)
f.show()
r=qApp.exec_()
if __name__=="__main__":
qApp=QApplication(sys.argv)
Home()
I found an even cleaner method for working with this, that does not require preemptive conversion after each edit at all. Instead it takes the .ui file itself, so all you need to do is restart the program itself to update the design.
import sys
import os
from PyQt5.QtWidgets import QMainWindow, QApplication
from PyQt5 import uic
path = os.path.dirname(__file__) #uic paths from itself, not the active dir, so path needed
qtCreatorFile = "XXXXX.ui" #Ui file name, from QtDesigner, assumes in same folder as this .py
Ui_MainWindow, QtBaseClass = uic.loadUiType(path + qtCreatorFile) #process through pyuic
class MyApp(QMainWindow, Ui_MainWindow): #gui class
def __init__(self):
#The following sets up the gui via Qt
super(MyApp, self).__init__()
self.ui = Ui_MainWindow()
self.ui.setupUi(self)
#set up callbacks
self.ui.NAME OF CONTROL.ACTION.connect(self.test)
def test(self):
#Callback Function
if __name__ == "__main__":
app = QApplication(sys.argv) #instantiate a QtGui (holder for the app)
window = MyApp()
window.show()
sys.exit(app.exec_())
Note that this is Qt5. Qt5 and Qt4 are not API compatible, so it will be a little different in Qt4 (and presumably earlier as well).
I have almost the exact same question as the one found here:
Override shouldInterruptJavaScript in QWebPage with PySide
In my case though I want to override the copy and paste slots on QLineEdit
import sys
from PySide import QtGui, QtCore
class myLineEdit(QtGui.QLineEdit):
# FIXME: This is not working, the slot is not overriden!
#QtCore.Slot()
def copy(self):
print 'overridden copy event'
App.clipboard().setText('customized text')
return False
#QtCore.Slot()
def paste(self):
print 'overridden paste event'
self.setText('customized text')
return False
if __name__ == "__main__":
App = QtGui.QApplication(sys.argv)
Widget = myLineEdit()
Widget.show()
cmenu = Widget.createStandardContextMenu()
sys.exit(App.exec_())
I'm using Python 2.7.3, with PySide 1.2.2
I don't know if these methods are even supposed to be override-able, but I can't find any documentation that says they shouldn't be.
I also found this page
http://qt-project.org/faq/answer/is_it_possible_to_reimplement_non-virtual_slots
The page explains how certain kinds of slots get pointers set to them by functions that get called when the object is initialized (or something along those lines, I'm not as familiar with the C++).
Following this logic I added the createStandardContextMenu() call above in the hopes that it would reinitialize the slots for at least the context menu, but no luck.
Am I doing something wrong? Or should I try filing a bug report?
You cannot override QLineEdit.copy or QLineEdit.paste in such a way that they will be called internally by Qt.
In general, you can only usefully override or reimplement Qt functions that are defined as being virtual. The Qt Docs will always specify whether this is the case, and for QLineEdit, there are no public slots that are defined in that way.
There is also no easy workaround. There are a lot of different ways in which copy and paste operations (or their equivalents) can be invoked, such as keyboard shortcuts, context menu, drag and drop, etc. It can be done: but it's a lot of work to get complete control over all these sorts of operations. So you need to think carefully about what you're trying to achieve before deciding how to proceed.
I know this has been asked many times before. I read all of those threads, and my case seems different. Everybody else who has this trouble has a few straightforward causes that I think I’ve ruled out, such as:
Starting a timer with no event loop running
Starting/stopping a timer from a thread other than the one that created the timer
Failing to set the parent property of a widget, leading to problems with the order of destruction
Below I have a minimal code sample that demonstrates the problem. Notice that I’ve started no threads or timers. I also have set the parent of every widget. If I remove the graph widgets, the problem goes away, so one is tempted to blame pyQtGraph, however, if I include the plot widgets but exclude all the blank tabs (i.e. every tab except tabCatchaTiger), the problem also goes away, and that seems to vindicate pyQtGraph.
Versions:
Windows 7
Python 2.7.8
Wing IDE 5.0.9-1
PyQt 4.11.1
PyQwt 5.2.1
PyQtGraph 0.9.8
Test case:
from PyQt4 import Qt, QtGui, QtCore
import PyQt4.Qwt5 as Qwt
import pyqtgraph as pg
pg.functions.USE_WEAVE = False # Lets pyqtgraph plot without gcc
pg.setConfigOption('background', 'w')
pg.setConfigOption('foreground', 'k')
# GUI for visualizing data from database
class crashyGUI(QtGui.QWidget) :
def __init__(self) :
# Make the window
QtGui.QWidget.__init__(self)
self.resize(700, QtGui.QDesktopWidget().screenGeometry(self).height()*.85)
self.setWindowTitle('Data Visualization')
# Create tab interface
tabWidget = QtGui.QTabWidget(self)
# define the tab objects
self.tabEeny = QtGui.QWidget(tabWidget)
self.tabMeeny = QtGui.QWidget(tabWidget)
self.tabMiney = QtGui.QWidget(tabWidget)
self.tabMoe = QtGui.QWidget(tabWidget)
self.tabCatchaTiger = QtGui.QWidget(tabWidget)
self.tabByThe = QtGui.QWidget(tabWidget)
self.tabToe = QtGui.QWidget(tabWidget)
# Initialize the tab objects
self.initTabCatchaTiger()
###########################################
############### Main Layout ###############
###########################################
tabWidget.addTab(self.tabEeny, 'Eeny')
tabWidget.addTab(self.tabMeeny, 'Meeny')
tabWidget.addTab(self.tabMiney, 'Miney')
tabWidget.addTab(self.tabMoe, 'Moe')
tabWidget.addTab(self.tabCatchaTiger, 'Catch a Tiger')
tabWidget.addTab(self.tabByThe, 'By The')
tabWidget.addTab(self.tabToe, 'Toe')
self.mainLayout = QtGui.QVBoxLayout(self)
self.mainLayout.addWidget(tabWidget)
self.setLayout(self.mainLayout)
def initTabCatchaTiger(self):
###########################################
############# ADC Capture Tab #############
###########################################
# define tab layout
grid = QtGui.QGridLayout(self.tabCatchaTiger)
# create copy of adc plot and add to row 3 of the grid
self.catchaTigerPlot1 = pg.PlotWidget(name = 'Catch a Tiger 1', parent = self.tabCatchaTiger)
self.catchaTigerPlot1.setTitle('Catch a Tiger 1')
grid.addWidget(self.catchaTigerPlot1, 2, 0, 1, 8)
self.catchaTigerPlot2 = pg.PlotWidget(name = 'Catch a Tiger 2', parent = self.tabCatchaTiger)
self.catchaTigerPlot2.setTitle('Catch a Tiger 2')
grid.addWidget(self.catchaTigerPlot2, 3, 0, 1, 8)
# set layout for tab
self.tabCatchaTiger.setLayout(grid)
def closeEvent(self, event) :
pass
def main() :
# open a QApplication and dialog() GUI
app = QtGui.QApplication([])
windowCrashy = crashyGUI()
windowCrashy.show()
app.exec_()
main()
There seem to be two closely-related issues in the example.
The first one causes Qt to print the QObject::startTimer: QTimer can only be used with threads started with QThread messages on exit.
The second one (which may not affect all users) causes Qt to print QPixmap: Must construct a QApplication before a QPaintDevice, and then dump core on exit.
Both of these issues are caused by python deleting objects in an unpredicable order when it exits.
In the example, the second issue can be fixed by adding the following line to the __init__ of the top-level window:
self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
Unless QApplication.setQuitOnLastWindowClosed has been changed to False, this will ensure that the application quits at the right time, and that Qt has a chance to automatically delete all the children of the top-level window before the python garbage-collector gets to work.
However, for this to be completely successful, all the relevant objects must be linked together in a parent-child hierarchy. The example code does this where it can, but there seem to be some critical places in the initialization of the PlotWidget class where it is not done.
In particular, there is nothing to ensure that the central item of the PlotWidget has a parent set when it is created. If the relevant part of the code is changed to this:
class PlotWidget(GraphicsView):
...
def __init__(self, parent=None, background='default', **kargs):
GraphicsView.__init__(self, parent, background=background)
...
self.plotItem = PlotItem(**kargs)
# make sure the item gets a parent
self.plotItem.setParent(self)
self.setCentralItem(self.plotItem)
then the first issue with the QTimer messages also goes away.
Here's a better answer:
You are allowing the QApplication to be collected before python exits. This causes two different issues:
The QTimer error messages are caused by pyqtgraph trying to track its ViewBoxes after the QApplication has been destroyed.
The crash appears to be intrinsic to Qt / PyQt. The following crashes in the same way:
from PyQt4 import Qt, QtGui, QtCore
def main() :
app = QtGui.QApplication([])
x = QtGui.QGraphicsView()
s = QtGui.QGraphicsScene()
x.setScene(s)
x.show()
app.exec_()
main()
You can fix it by adding global app to your main function, or by creating the QApplication at the module level.
Try to write this in block of __init__:
self.setAttribute(Qt.WA_DeleteOnClose)
Personally, I don't put any effort into chasing exit crashes anymore--just use pg.exit() and be done with it.
(but if you do happen to find a bug in pyqtgraph, don't hesitate to open an issue on github)
I had this happen as well and in my case it was caused by a call to deleteLater() on the aboutToQuit-Signal of the application, like so:
def closeEvent(self, *args, **kwargs):
self.deleteLater()
if __name__ == "__main__":
application = QtWidgets.QApplication(sys.argv)
window = testApplication()
# Handle application exit
application.aboutToQuit.connect(window.closeEvent)
# System exit
sys.exit(application.exec_())
Getting rid of the deleteLater on the whole window seemed to solve it.
I'm adding an item to a QListWidget, and although I can get the specifics of the item back from the QListQidget, the new item never appears on the screen. Is it possible to refresh the QListWidget to have it update to display newer contents?
>>>myQListWidget.addItem("Hello")
>>>print self.myQListWidget.item(0).text()
Hello
I'm doing this in Python, but if you have the solution in C++ I can easily convert it.
Thanks!
--Erin
You can update the widget's view by calling update() or repaint(), the second function is asynchronous and forces widget to update immediately. But the QListWidget should update automatically after insertion without calling any extra functions, if not, then the problem could be that Qt can't process the paint events. Then you have to call QCoreApplication::processEvents(), but I am not sure if it is your problem.
Hmm... I'm not seeing that behavior.
import sys
from PyQt4 import QtCore
from PyQt4 import QtGui
a = QtGui.QApplication(sys.argv)
w = QtGui.QListWidget()
w.setWindowTitle('example')
w.show()
w.addItem("test 1") # shows up
w.addItem("test 2") # also shows up
EDIT: Removed chevrons so the code can be copied/pasted
I saw similar behavior as user671110 with PyQt5 (5.9.2). In my case using the suggestion from this qt forum worked.
Using the adapted sample code from jkerian:
import sys
from PyQt5 import QtWidgets
a = QtWidgets.QApplication(sys.argv)
w = QtWidgets.QListWidget()
w.setWindowTitle('example')
w.show()
w.addItem("test 1") # Item 1 does NOT show up
w.repaint() # Item 1 does NOT show up
QtCore.QCoreApplication.processEvents()
# Item 1 DOES show up
w.addItem("test 2")
# Item 2 does NOT show up
QtCore.QCoreApplication.processEvents()
# Item 2 DOES show up
w.addItem("test 3")
# Item 3 does NOT show up
a.exec_() # All items shows up
This is kind of expected as the GUI is refreshed with event processing. Still THe doc mentioned that repaint() could be use to perform an asynchronous refresh but it does not seems to be working, or I use it wrongly.