I would like to know how to implement QProgressBar, which shows the progress of calculation in main thread.
Please refer to below codes.
import sys
from PySide2.QtWidgets import QApplication, QWidget, QPushButton, QVBoxLayout, QProgressBar
from PySide2.QtCore import QThread
class BarThread(QThread):
# Progress Bar UI Definition
def __init__(self):
QThread.__init__(self)
self.window = QWidget()
self.pgsb = QProgressBar()
self.lay = QVBoxLayout()
self.lay.addWidget(self.pgsb)
self.window.setLayout(self.lay)
self.isRun = False
# Thread Function Definition
def run(self):
self.window.show()
while self.isRun:
self.pgsb.setValue(self.percent)
print(self.percent)
if self.percent == 100:
self.isRun = False
class Tool(QWidget):
# Main UI Definition
def __init__(self):
windowWidth = 300
windowHeight = 300
QWidget.__init__(self)
self.setWindowTitle("Example")
self.resize(windowWidth, windowHeight)
self.bt = QPushButton('Numbering')
self.layout = QVBoxLayout()
self.layout.addWidget(self.bt)
self.setLayout(self.layout)
# Main Function Link Definition
self.bt.clicked.connect(self.numbering)
# Main Function Definition
def numbering(self):
bth = BarThread()
bth.start()
bth.isRun = True
for x in range(0,100000):
bth.percent = x/1000
print(x)
if __name__ == "__main__":
app = QApplication(sys.argv)
widget = Tool()
widget.show()
sys.exit(app.exec_())
You can copy and paste directly onto your python IDE.
(it needs PySide2. It can be installed with 'pip install pyside2' in your prompt).
This code executes simple numbering, however, this doesn't show numbering progress.
How can I solve this problem? Thank you in advance.
P.S. I'm using Windows 10 with PyCharm.
You have at least the following errors:
You must not modify the GUI from another thread, in your case the run method is executed in another thread but you try to modify the value of the QProgressBar, in addition to displaying a widget which is not allowed. If you want to modify the GUI with the information provided in the execution in the secondary thread you must do it through signals since they are thread-safe
The for loop is the blocking task so it must be executed in another thread.
Considering the above, the solution is:
import sys
from PySide2.QtWidgets import (
QApplication,
QWidget,
QPushButton,
QVBoxLayout,
QProgressBar,
)
from PySide2.QtCore import QThread, Signal
class ProgressWidget(QWidget):
def __init__(self, parent=None):
super(ProgressWidget, self).__init__(parent)
self.pgsb = QProgressBar()
lay = QVBoxLayout(self)
lay.addWidget(self.pgsb)
class BarThread(QThread):
progressChanged = Signal(int)
def run(self):
percent = 0
for x in range(0, 100000):
percent = x / 100
self.progressChanged.emit(percent)
class Tool(QWidget):
"""Main UI Definition"""
def __init__(self, parent=None):
super(Tool, self).__init__(parent)
self.setWindowTitle("Example")
self.resize(300, 300)
self.bt = QPushButton("Numbering")
layout = QVBoxLayout(self)
layout.addWidget(self.bt)
# Main Function Link Definition
self.bt.clicked.connect(self.numbering)
self.bar_thread = BarThread(self)
self.progress_widget = ProgressWidget()
self.bar_thread.progressChanged.connect(self.progress_widget.pgsb.setValue)
# Main Function Definition
def numbering(self):
self.bar_thread.start()
self.progress_widget.show()
def closeEvent(self, event):
super(Tool, self).closeEvent(event)
self.bar_thread.quit()
self.bar_thread.wait()
if __name__ == "__main__":
app = QApplication(sys.argv)
widget = Tool()
widget.show()
sys.exit(app.exec_())
Related
i want to change slider position, when the self.factor is changed during set_parameter(). More precisely, how to update slider position as the value changes during computation?
from PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QVBoxLayout, QPushButton, QSlider, QShortcut
from PyQt5.QtGui import QKeySequence
class Params():
def __init__(self):
self.factor = 0
def get_parameter(self):
return self.factor
def set_parameter(self, val):
self.factor =val
class SliderWidget(QWidget):
def __init__(self, param: Params):
QWidget.__init__(self)
self.params = param
layout = QVBoxLayout()
self.setLayout(layout)
self.slider = QSlider()
self.slider.valueChanged.connect(self.on_param_change)
layout.addWidget(self.slider)
self.slider.setMinimum(4)
self.slider.setMaximum(8)
def on_param_change(self):
value = self.params.get_parameter()
self.slider.setValue(value)
class Window(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
self.box = QVBoxLayout()
self.params = Params()
self.scene = SliderWidget(self.params)
self.setCentralWidget(self.scene)
self.shortcutUp = QShortcut(QKeySequence('Ctrl+W'), self)
self.shortcutDw = QShortcut(QKeySequence('Ctrl+S'), self)
self.shortcutUp.activated.connect(self.up)
self.shortcutDw.activated.connect(self.down)
def up(self):
print('up')
value = (self.params.get_parameter() + 1)
self.params.set_parameter(value)
def down(self):
print('down')
value = (self.params.get_parameter() -1)
self.params.set_parameter(value)
import sys
if __name__ == '__main__':
app = QApplication(sys.argv)
win = Window()
win.show()
app.exec_()
You need to go through threading.
There is an exact procedure to achieve threading using PyQt5.
If you are not following it correctly, the application will crash without any error messages.
You will need the QThread lib and create workers to overwrite run method of QThread.
Here some link describing this:
https://www.youtube.com/watch?v=G7ffF0U36b0
https://realpython.com/python-pyqt-qthread/#using-qthread-to-prevent-freezing-guis
Here is the code with buttons:
from PyQt5.QtCore import QObject, QThread, pyqtSignal
class Worker(QObject): # Step 1: Create a worker class
finished = pyqtSignal()
progress = pyqtSignal(int)
def run(self):
"""Long-running task."""
for i in range(5):
sleep(1)
self.progress.emit(i + 1)
self.finished.emit()
class Window(QMainWindow):
# Snip...
def runLongTask(self):
# Step 2: Create a QThread object
self.thread = QThread()
# Step 3: Create a worker object
self.worker = Worker()
# Step 4: Move worker to the thread
self.worker.moveToThread(self.thread)
# Step 5: Connect signals and slots
self.thread.started.connect(self.worker.run)
self.worker.finished.connect(self.thread.quit)
self.worker.finished.connect(self.worker.deleteLater)
self.thread.finished.connect(self.thread.deleteLater)
self.worker.progress.connect(self.reportProgress)
# Step 6: Start the thread
self.thread.start()
# Final resets
self.longRunningBtn.setEnabled(False)
self.thread.finished.connect(
lambda: self.longRunningBtn.setEnabled(True)
)
self.thread.finished.connect(
lambda: self.stepLabel.setText("Long-Running Step: 0")
)
Using PySide2 (which is basically the same as PyQt5), I created this minor example. It displays a single QSlider. If you press Ctrl+W or Ctrl+S, the QShortcut is activated and it respectively increases or decreases the QSlider by +1 or -1.
Here's the script:
from PySide2.QtWidgets import QApplication, QMainWindow, QWidget, QVBoxLayout, QPushButton, QSlider, QShortcut
from PySide2.QtGui import QKeySequence
class Scene(QWidget):
def __init__(self):
QWidget.__init__(self)
layout = QVBoxLayout()
self.setLayout(layout)
self.slider = QSlider()
layout.addWidget(self.slider)
self.slider.setMinimum(4)
self.slider.setMaximum(8)
class Window(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
self.scene = Scene()
self.setCentralWidget(self.scene)
self.shortcutUp = QShortcut(QKeySequence('Ctrl+W'), self)
self.shortcutDw = QShortcut(QKeySequence('Ctrl+S'), self)
self.shortcutUp.activated.connect(self.up)
self.shortcutDw.activated.connect(self.down)
def up(self):
print('up')
self.scene.slider.setValue(self.scene.slider.value()+1)
def down(self):
print('down')
self.scene.slider.setValue(self.scene.slider.value()-1)
if __name__ == '__main__':
app = QApplication()
win = Window()
win.show()
app.exec_()
I used a QShortcut so I didn't have to create a menubar, and set a shortcut there. It makes the exmaple smaller but with the same behaviour.
I have an application where I run some process in a second thread and at some point, given a certain condition, another dialog window opens, which halts the process until you confirm something. This causes the following error message:
QObject: Cannot create children for a parent that is in a different thread.
(Parent is QApplication(0x1f9c82383d0), parent's thread is QThread(0x1f9c7ade2a0), current thread is QThread(0x1f9c8358800)
Interestingly, if you also move your cursor over the MainWindow while the process is running, and before the new dialog pops up, it also produces this error message a couple of times:
QBasicTimer::stop: Failed. Possibly trying to stop from a different thread
Very strange. Because it only occurs if you move your cursor over the MainWindow.
Now, in my application, I actually load an interface for the new dialog that pops up using PyQt5.uic.loadUi, and this hasn't caused any problems. However, when I was creating the example for this post, another issue occurred, due to the fact that I was setting the layout of the new dialog during its initialization:
QObject::setParent: Cannot set parent, new parent is in a different thread
Which results in the application crashing:
Process finished with exit code -1073741819 (0xC0000005)
I'm obviously doing something wrong here regarding the threading I would guess, but I don't know what. I am especially baffled by the fact that I cannot set the layout of the new dialog during its initialization, while using loadUi is totally fine. Here is my example code:
import sys
import time
import numpy as np
from PyQt5.QtCore import QObject, pyqtSignal, QThread
from PyQt5.QtWidgets import (
QDialog, QApplication, QPushButton, QGridLayout, QProgressBar, QLabel
)
class SpecialDialog(QDialog):
def __init__(self):
super().__init__()
btn = QPushButton('pass variable')
btn.clicked.connect(self.accept)
layout = QGridLayout()
layout.addWidget(btn)
# self.setLayout(layout)
self.variable = np.random.randint(0, 100)
class Handler(QObject):
progress = pyqtSignal(int)
finished = pyqtSignal(int)
def __init__(self):
super().__init__()
self._isRunning = True
self._success = False
def run(self):
result = None
i = 0
while i < 100 and self._isRunning:
if i == 50:
dialog = SpecialDialog()
dialog.exec_()
result = dialog.variable
time.sleep(0.01)
i += 1
self.progress.emit(i)
if i == 100:
self._success = True
self.finished.emit(result)
def stop(self):
self._isRunning = False
class MainWindow(QDialog):
def __init__(self):
super().__init__()
btn = QPushButton('test')
btn.clicked.connect(self.run_test)
self.pbar = QProgressBar()
self.resultLabel = QLabel('Result:')
layout = QGridLayout(self)
layout.addWidget(btn)
layout.addWidget(self.pbar)
layout.addWidget(self.resultLabel)
self.setLayout(layout)
self.handler = None
self.handler_thread = QThread()
self.result = None
def run_test(self):
self.handler = Handler()
self.handler.moveToThread(self.handler_thread)
self.handler.progress.connect(self.progress)
self.handler.finished.connect(self.finisher)
self.handler_thread.started.connect(self.handler.run)
self.handler_thread.start()
def progress(self, val):
self.pbar.setValue(val)
def finisher(self, result):
self.result = result
self.resultLabel.setText(f'Result: {result}')
self.pbar.setValue(0)
self.handler.stop()
self.handler.progress.disconnect(self.progress)
self.handler.finished.disconnect(self.finisher)
self.handler_thread.started.disconnect(self.handler.run)
self.handler_thread.terminate()
self.handler = None
if __name__ == '__main__':
app = QApplication(sys.argv)
GUI = MainWindow()
GUI.show()
sys.exit(app.exec_())
EDIT
I forgot to mention that I already found this post, which may be related to my problem, however, I don't undestand the reasoning of the solution in the top answer, and more importantly, I don't speak what I believe is C++.
You cannot create or modify a GUI element from a secondary thread and this is signaled by the error message.
You have to redesign the Handler class, with your requirement you must divide run into 2 methods, the first method will generate progress up to 50% where the GUI will open the dialogue, obtain the result and launch the second method.
import sys
import time
import numpy as np
from functools import partial
from PyQt5.QtCore import QObject, pyqtSignal, pyqtSlot, QThread, QTimer
from PyQt5.QtWidgets import (
QDialog,
QApplication,
QPushButton,
QGridLayout,
QProgressBar,
QLabel,
)
class SpecialDialog(QDialog):
def __init__(self):
super().__init__()
btn = QPushButton("pass variable")
btn.clicked.connect(self.accept)
layout = QGridLayout()
layout.addWidget(btn)
# self.setLayout(layout)
self.variable = np.random.randint(0, 100)
class Handler(QObject):
progress = pyqtSignal(int)
finished = pyqtSignal(int)
def __init__(self):
super().__init__()
self._isRunning = True
self._success = False
#pyqtSlot()
def task1(self):
i = 0
while i <= 50 and self._isRunning:
time.sleep(0.01)
i += 1
self.progress.emit(i)
#pyqtSlot(int)
def task2(self, result):
i = 50
while i < 100 and self._isRunning:
time.sleep(0.01)
i += 1
self.progress.emit(i)
if i == 100:
self._success = True
self.finished.emit(result)
def stop(self):
self._isRunning = False
class MainWindow(QDialog):
def __init__(self):
super().__init__()
btn = QPushButton("test")
btn.clicked.connect(self.run_test)
self.pbar = QProgressBar()
self.resultLabel = QLabel("Result:")
layout = QGridLayout(self)
layout.addWidget(btn)
layout.addWidget(self.pbar)
layout.addWidget(self.resultLabel)
self.setLayout(layout)
self.handler = None
self.handler_thread = QThread()
self.result = None
def run_test(self):
self.handler = Handler()
self.handler.moveToThread(self.handler_thread)
self.handler.progress.connect(self.progress)
self.handler.finished.connect(self.finisher)
self.handler_thread.started.connect(self.handler.task1)
self.handler_thread.start()
#pyqtSlot(int)
def progress(self, val):
self.pbar.setValue(val)
if val == 50:
dialog = SpecialDialog()
dialog.exec_()
result = dialog.variable
wrapper = partial(self.handler.task2, result)
QTimer.singleShot(0, wrapper)
def finisher(self, result):
self.result = result
self.resultLabel.setText(f"Result: {result}")
self.pbar.setValue(0)
self.handler.stop()
self.handler_thread.quit()
self.handler_thread.wait()
if __name__ == "__main__":
app = QApplication(sys.argv)
GUI = MainWindow()
GUI.show()
sys.exit(app.exec_())
There has been a small problem with a little project of mine using PyQt5. I tried to add a random QWidget (in this example a QPushbutton) to a custom QWidget. However, I don't understand the behavior of the "setParent" function. When I use it outside of the custom QWidget, the QPushButton is displayed. When I use it in a declared function of the custom Widget, the QPushButton is occluded and I have no chance of displaying it outside of adding a layout (which I don't want). Here an example of the source code:
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *
class customWidget(QWidget):
def __init__(self):
super().__init__()
self.addButton()
def addButton(self):
button = QPushButton('not_showing')
button.setParent(self)
if __name__ == '__main__':
app = QApplication(sys.argv)
w = QWidget()
button = QPushButton('showing')
button.setParent(w)
button.move(50,50)
w.resize(600,600)
w.move(1000,300)
w.setWindowTitle('Simple')
w.show()
sys.exit(app.exec_())
There is no change, when adding the parent during the initialization of the QPushButton.
When the function addButton exits, the button is removed.
If you want to see the button, try this:
class customWidget(QWidget):
def __init__(self):
super().__init__()
self.addButton()
self.button = None
def addButton(self):
if self.button is None:
self.button = QPushButton('not_showing')
self.button.setParent(self)
You do not have this problem in the main function because this function does not return until the application is stopped.
EDIT: The comment was right, but you also missed some arguments. This will work
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *
import sys
class customWidget(QWidget):
def __init__(self, parent=None):
super(customWidget, self).__init__(parent)
self.addButton()
def addButton(self):
button = QPushButton('not_showing')
button.setParent(self)
if __name__ == '__main__':
app = QApplication(sys.argv)
w = customWidget()
button = QPushButton('showing')
button.setParent(w)
button.move(50,50)
w.resize(600,600)
w.move(1000,300)
w.setWindowTitle('Simple')
w.show()
sys.exit(app.exec_())
One day old in terms of experience with PyQT, I followed sample code HERE to do this, but I am clueless as to how I could separate the start download part from the start GUI part, so that I can instead start that when I press the OK (startBtn)button. Also, know the command I do doesn't do anything but give you an error, but I know that works.
Any help appreciated!
from PyQt5.QtWidgets import QApplication, QWidget, QMainWindow, QAction, qApp, QDesktopWidget, QPushButton, QHBoxLayout, QVBoxLayout, QTextEdit
from PyQt5.QtGui import QIcon
from PyQt5.QtCore import QThread, QProcess
import sys
class GUI(QProcess):
def __init__(self):
super().__init__()
# Create an instance variable here (of type QTextEdit)
startBtn = QPushButton('OK')
stopBtn = QPushButton('Cancel')
#startBtn.clicked.connect()
stopBtn.clicked.connect(qApp.exit)
self.hbox = QHBoxLayout()
self.hbox.addStretch(1)
self.hbox.addWidget(startBtn)
self.hbox.addWidget(stopBtn)
self.edit = QTextEdit()
self.edit.setWindowTitle("QTextEdit Standard Output Redirection")
self.vbox = QVBoxLayout()
self.vbox.addStretch(1)
self.vbox.addWidget(self.edit)
self.vbox.addLayout(self.hbox)
#setLayout(self.vbox)
self.central=QWidget()
#self.vbox.addWidget(self.edit)
self.central.setLayout(self.vbox)
self.central.show()
def readStdOutput(self):
self.edit.append(str(self.readAllStandardOutput()))
def main():
app = QApplication(sys.argv)
qProcess = GUI()
qProcess.setProcessChannelMode(QProcess.MergedChannels);
qProcess.start("youtube-dl")
qProcess.readyReadStandardOutput.connect(qProcess.readStdOutput);
return app.exec_()
if __name__ == '__main__':
main()
2 notes:
If you also know how to disable the OK button when you press it, until the process is finished, then I'd love to know.
Not all imports are used, but I can clean that later. PyCharm show which is used and not. Cleanup is for later.
To do what you ask you have to have some considerations:
youtube-dl requires parameters, like the url, for this I have placed a QLineEdit.
To know when the process starts and ends, we use the signal: stateChanged(newState)
Complete code:
import sys
from PyQt5.QtCore import QProcess
from PyQt5.QtWidgets import QApplication, QWidget, QPushButton, QHBoxLayout, QVBoxLayout, QTextEdit, QLabel, QLineEdit
class GUI(QProcess):
def __init__(self, parent=None):
super(GUI, self).__init__(parent=parent)
# Create an instance variable here (of type QTextEdit)
self.startBtn = QPushButton('OK')
self.stopBtn = QPushButton('Cancel')
self.hbox = QHBoxLayout()
self.hbox.addStretch(1)
self.hbox.addWidget(self.startBtn)
self.hbox.addWidget(self.stopBtn)
self.label = QLabel("Url: ")
self.lineEdit = QLineEdit()
self.lineEdit.textChanged.connect(self.EnableStart)
self.hbox2 = QHBoxLayout()
self.hbox2.addWidget(self.label)
self.hbox2.addWidget(self.lineEdit)
self.edit = QTextEdit()
self.edit.setWindowTitle("QTextEdit Standard Output Redirection")
self.vbox = QVBoxLayout()
self.vbox.addStretch(1)
self.vbox.addLayout(self.hbox2)
self.vbox.addWidget(self.edit)
self.vbox.addLayout(self.hbox)
self.central = QWidget()
self.central.setLayout(self.vbox)
self.central.show()
self.startBtn.clicked.connect(self.startDownload)
self.stopBtn.clicked.connect(self.kill)
self.stateChanged.connect(self.slotChanged)
self.EnableStart()
def slotChanged(self, newState):
if newState == QProcess.NotRunning:
self.startBtn.setDisabled(False)
elif newState == QProcess.Running:
self.startBtn.setDisabled(True)
def startDownload(self):
self.start("youtube-dl", [self.lineEdit.text()])
def readStdOutput(self):
self.edit.append(str(self.readAllStandardOutput()))
def EnableStart(self):
self.startBtn.setDisabled(self.lineEdit.text() == "")
def main():
app = QApplication(sys.argv)
qProcess = GUI()
qProcess.setProcessChannelMode(QProcess.MergedChannels)
qProcess.readyReadStandardOutput.connect(qProcess.readStdOutput)
return app.exec_()
if __name__ == '__main__':
main()
Screenshot:
I want use the autoconnection feature. I am using this example:
http://www.eurion.net/python-snippets/snippet/Connecting%20signals%20and%20slots.html
it works, but I want to create my own signals and own slots, the example using built in signals.
for example, here are a custom signal with a custom slot, but don't works:
import sys
from PyQt4 import QtGui, QtCore
class SignalsAndSlots(QtGui.QWidget):
testSignal = QtCore.pyqtSignal(str,name='testSignal')
def __init__(self):
QtGui.QMainWindow.__init__(self)
self.setObjectName('testObject')
self.label = QtGui.QLabel(self)
QtCore.QMetaObject.connectSlotsByName(self)
self.emitSignal()
def emitSignal(self):
self.testSignal.emit('message')
#QtCore.pyqtSlot(str,name='on_testObject_testSignal')
def autoSlot(self,msg):
self.label.setText(msg)
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
gui = SignalsAndSlots()
gui.show()
app.exec_()
Thanks a lot
Ber is right. This what the pyqt documentation says:
QMetaObject.connectSlotsByName searches recursively for all child objects of the given object [...]
Here is a simple example with custom signals :
import sys
from PyQt4 import QtGui, QtCore
class CustomButton(QtGui.QPushButton):
custom_clicked = QtCore.pyqtSignal(str, name='customClicked')
def mousePressEvent(self, event):
self.custom_clicked.emit("Clicked!")
class SignalsAndSlots(QtGui.QWidget):
def __init__(self):
QtGui.QMainWindow.__init__(self)
layout = QtGui.QHBoxLayout(self)
self.custom_button = CustomButton("Press Me", self)
self.custom_button.setObjectName('customButton')
self.label = QtGui.QLabel("Nothing...", parent=self)
layout.addWidget(self.custom_button)
layout.addWidget(self.label)
QtCore.QMetaObject.connectSlotsByName(self)
#QtCore.pyqtSlot(str, name='on_customButton_customClicked')
def autoSlot(self, msg):
self.label.setText(msg)
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
gui = SignalsAndSlots()
gui.show()
app.exec_()
But I think you should consider not using the object names. New-style signal connection is way neater. Here is the same application :
import sys
from PyQt4 import QtGui, QtCore
class CustomButton(QtGui.QPushButton):
custom_clicked = QtCore.pyqtSignal(str)
def mousePressEvent(self, event):
self.custom_clicked.emit("Clicked!")
class SignalsAndSlots(QtGui.QWidget):
def __init__(self):
QtGui.QMainWindow.__init__(self)
layout = QtGui.QHBoxLayout(self)
self.custom_button = CustomButton("Press Me", self)
self.custom_button.setObjectName('customButton')
self.label = QtGui.QLabel("Nothing...", parent=self)
layout.addWidget(self.custom_button)
layout.addWidget(self.label)
self.custom_button.custom_clicked.connect(self.on_clicked)
def on_clicked(self, msg):
self.label.setText(msg)
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
gui = SignalsAndSlots()
gui.show()
app.exec_()
I investigated a bit into the doc. of QtCore.QMetaObject.connectSlotsByName().
For this, I made an MCVE to collect things not working vs. things working:
#!/usr/bin/python3
import sys
from PyQt5.QtCore import QT_VERSION_STR
from PyQt5.QtCore import QMetaObject, pyqtSlot
from PyQt5.QtWidgets import QApplication, QMainWindow, QVBoxLayout, QPushButton, QWidget
class MainWindow(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
# build GUI
qMain = QWidget()
qVBox = QVBoxLayout()
qBtnPreview1 = QPushButton("Preview 1")
qBtnPreview1.setObjectName("preview1")
qVBox.addWidget(qBtnPreview1)
qBtnPreview2 = QPushButton("Preview 2")
qBtnPreview2.setObjectName("preview2")
qVBox.addWidget(qBtnPreview2)
qBtnPreview3 = QPushButton("Preview 3")
qBtnPreview3.setObjectName("preview3")
qVBox.addWidget(qBtnPreview3)
qBtnPreview4 = QPushButton("Preview 4")
qBtnPreview4.setObjectName("preview4")
qVBox.addWidget(qBtnPreview4)
qBtnPreview5 = QPushButton("Preview 5")
qBtnPreview5.setObjectName("preview5")
qVBox.addWidget(qBtnPreview5)
qBtnPreview6 = QPushButton("Preview 6")
qBtnPreview6.setObjectName("preview6")
qVBox.addWidget(qBtnPreview6)
qMain.setLayout(qVBox)
self.setCentralWidget(qMain)
# install signal handlers
qBtnPreview1.clicked.connect(lambda: print("preview1 clicked."))
qBtnPreview2.clicked.connect(lambda: print("preview2 clicked."))
qBtnPreview3.clicked.connect(lambda: print("preview3 clicked."))
qBtnPreview4.clicked.connect(lambda: print("preview4 clicked."))
qBtnPreview5.clicked.connect(lambda: print("preview5 clicked."))
qBtnPreview6.clicked.connect(lambda: print("preview6 clicked."))
QMetaObject.connectSlotsByName(self)
#pyqtSlot()
def preview1(self):
print("MainWindow.preview1() called.")
#pyqtSlot()
def preview2_clicked(self):
print("MainWindow.preview2_clicked() called.")
#pyqtSlot()
def on_preview3(self):
print("MainWindow.on_preview3() called.")
#pyqtSlot()
def on_preview4_clicked(self):
print("MainWindow.on_preview4_clicked() called.")
#pyqtSlot(name='on_preview5_clicked')
def preview5_clicked(self):
print("MainWindow.preview5_clicked() called.")
def on_preview6_clicked(self):
print("MainWindow.on_preview6_clicked() called.")
if __name__ == '__main__':
print("Qt Version: {}".format(QT_VERSION_STR))
app = QApplication(sys.argv)
# build GUI
qWinMain = MainWindow()
qWinMain.show()
# runtime loop
sys.exit(app.exec_())
Output:
$ ./testQMetaObjectConnectSlotsByName.py
Qt Version: 5.9.3
After clicking each of the six buttons once, I got:
preview1 clicked.
preview2 clicked.
preview3 clicked.
preview4 clicked.
MainWindow.on_preview4_clicked() called.
preview5 clicked.
MainWindow.preview5_clicked() called.
preview6 clicked.
MainWindow.on_preview6_clicked() called.
MainWindow.on_preview6_clicked() called.
Observations:
MainWindow.preview1(), MainWindow.preview2_clicked(), MainWindow.on_preview3() were not connected. They don't follow the required convention of QtCore.QMetaObject.connectSlotsByName().
MainWindow.on_preview4_clicked() is connected by name – properly following the required name convention.
MainWindow.preview5_clicked() is connected as well – by giving the required name by #pyqtSlot(name='on_preview5_clicked').
MainWindow.on_preview6_clicked() is connected as well – even without marking it as slot explicitly. (However, it is called twice for any reason which might be undesirable.)
Explicit connections work in any case and appear more robust to me.
Further readings:
QMetaObject::connectSlotsByName() (Qt5 C++ doc.)
Connecting Slots By Name (PyQt5 doc.)
PyQt5.QtCore.pyqtSlot() (PyQt5 doc.).
Actually, this was my answer to another question (SO: How to display two images in each Qlabel PyQt5) until I realized that QtCore.QMetaObject.connectSlotsByName() unlikely plays a role in that question.
So, I moved it here where it may be more appropriate even although the question is a bit aged.