PyQt: give parent when creating a widget? - python

Let's assume I want to create a dialog box, a child of my main program:
from PyQt4 import QtGui, QtCore
class WizardJournal(QtGui.QDialog):
def __init__(self, parent):
super(WizardJournal, self).__init__(parent)
self.parent = parent
self.initUI()
def initUI(self):
self.parent.wizard = QtGui.QWidget()
self.ok_button = QtGui.QPushButton("OK", self)
self.vbox_global = QtGui.QVBoxLayout(self)
self.vbox_global.addWidget(self.ok_button)
self.paret.wizard.setLayout(self.vbox_global)
self.parent.wizard.show()
if __name__ == '__main__':
app = QtGui.QApplication(sys.argv)
parent = QtGui.QWidget()
obj = WizardJournal(parent)
sys.exit(app.exec_())
This dialog box will be opened and closed by my main program. What is better regarding memory consumption:
self.ok_button = QtGui.QPushButton("OK", self)
self.ok_button = QtGui.QPushButton("OK")
Basically, I would like to know if I should mention the parent widget when I create a widget. When I will close this dialog box, will the OK button be released from memory if I didn't mention the parent widget when I created it ?

Given the way your example is currently structured, neither the dialog nor any of its child widgets will be deleted when it is closed.
You can see this by changing the end of the example to look like this:
app.exec_()
print('\n'.join(repr(w) for w in app.allWidgets()))
which will give output like this (once the dialog is closed):
<__main__.WizardJournal object at 0x7fcd850f65e8>
<PyQt4.QtGui.QPushButton object at 0x7fcd850f6708>
<PyQt4.QtGui.QWidget object at 0x7fcd850f6558>
<PyQt4.QtGui.QDesktopWidget object at 0x7fcd850f6828>
<PyQt4.QtGui.QWidget object at 0x7fcd850f6678>
In PyQt, you have to be aware that there may be two kinds of reference held for a object: one on the Python side (the PyQt wrapper object) and one on the C++ side (the underlying Qt object). So to fully delete an object, you need to remove all of these references.
In general, Qt does not delete objects unless you explictly tell it to do so. This is something you need to be aware of when creating dialogs with a parent, because it is very easy to produce a memory leak otherwise. It is common to see code written like this:
def openDialog(self):
dialog = MyDialog(self)
dialog.show()
Which looks harmless at first glance - but the method will create a new dialog every time it is called, and Qt will end up holding on to every single one of them (because of the parent reference on the C++ side). One way to avoid this is to re-write the method so that it only keeps a reference on the Python side:
def openDialog(self):
self.dialog = MyDialog()
self.dialog.show()
But what to do about a modal dialog, which must have a parent? In that case, you could initialise the dialog class like this:
class MyDialog(QtGui.QDialog):
def __init__(self, parent):
super(MyDialog, self).__init__(parent)
self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
And now Qt will automatically delete the dialog when it is closed, and also recursively delete all of its child objects as well. This will just leave behind an empty PyQt wrapper object, which will (eventually) be removed by the Python garbage-collector.
So for your particular example, I think I would re-write it to look something like this:
import sys
from PyQt4 import QtGui, QtCore
class WizardJournal(QtGui.QDialog):
def __init__(self, parent):
super(WizardJournal, self).__init__(parent)
self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
self.initUI()
def initUI(self):
self.ok_button = QtGui.QPushButton("OK", self)
layout = QtGui.QVBoxLayout(self)
layout.addWidget(self.ok_button)
self.show()
if __name__ == '__main__':
app = QtGui.QApplication(sys.argv)
parent = QtGui.QWidget()
obj = WizardJournal(parent)
app.exec_()
print('\n'.join(repr(w) for w in app.allWidgets()))
The dialog class is now completely self-contained, and there is only one external python reference to the instance of it. (If you need to access the parent widget from within the dialog class, you can use self.parent()).
PS: when widgets are added to a layout, they will be automatically re-parented to whatever top-level widget eventually contains the layout. So, strictly speaking, it is not necessary to explicitly set a parent for such widgets in your code.

Related

PySide2 main window not working after pop-up

I am building a graphical interface for an application using PySide2. My main window is a QMainWindow and I am trying to open a pop-up window, which is a QDialog, whenever a specific action is performed on the main window.
The pop-up opens perfectly fine. However, after it is open, the main window is no longer responsive. I believe the problem is that my application is overwriting the main window with the popup window.
The error message whenever I try to change the main window's stackedWidget index is:
AttributeError: 'Ui_popupHideSuccess' object has no attribute 'stackedWidget'
The code I am using to open the main window is the following:
if __name__ == '__main__':
app = QApplication(sys.argv)
myWindow = MainWindow()
myWindow.show()
sys.exit(app.exec_())
And the code I am using to open the pop-up window is the following:
def showPopupSuccessHide(self):
self.window = QDialog()
self.ui = Ui_popupHideSuccess()
self.ui.setupUi(self.window)
self.window.show()
The code for the windows themselves are on other files (as I am using QtDesigner for developing them). I believe it to be unnecessary for resolving this issue, but I can provide it if needed. What am I doing wrong here? I need to open pop-ups and still interact with the main window after.
I have no idea how to actually resolve this. I believe my error to be in the code I am using to open the pop-up window, but I'm not sure how to tweak it for it to work properly.
TL;DR
Do not overwrite self.ui.
Explanation
How uic composition works
One of the common ways of properly using pyuic generated files is to use composition (as opposed to multiple inheritance):
from PyQt5.QtWidgets import QApplication, QMainWindow, QDialog
from ui_mainWindow import Ui_MainWindow
class MyWindow(QMainWindow):
def __init__(self):
super().__init__()
self.ui = Ui_MainWindow()
self.ui.setupUi(self)
self.ui.myLineEdit.setText('some text')
This is perfectly fine, and makes sense: the concept is that an instance of the pyuic class (sometimes called "form class") is created and then the actual window is "set up" using that instance, with the self.ui object containing references to all widgets.
Note that making the ui persistent (using an instance attribute) is actually not a strict requirement, but it is usually necessary in order to be able to directly access the widgets, which is normally important to create signal connections or read properties.
But, if that's not required, it will work anyway: the widgets are automatically "reparented" to the main window (or their direct parents), and the garbage collection is not an issue as Qt will keep its own references internally (in Qt terms, "the window takes ownership").
Technically speaking, this is completely valid:
class MyWindow(QMainWindow):
def __init__(self):
super().__init__()
Ui_MainWindow().setupUi(self)
Then, we can still access the widgets using findChild and their object names (those set in Designer):
self.findChild(QLineEdit, 'myLineEdit').setText('some text')
Obviously, it is not very practical.
Creating "child" windows
When there is the need to create a child window (usually, a dialog), it's normally suggested to use an instance attribute to avoid garbage collection:
def createWindow(self):
self.window = QDialog()
self.window.show()
If that dialog also has a Designer file, we need to do something similar to what done at the beginning. Unfortunately, a very common mistake is to create the ui instance by using the same name:
def createWindow(self):
self.window = QDialog()
self.ui = Ui_Dialog()
self.ui.setupUi(self.window)
self.ui.anotherLineEdit.setText('another text')
self.window.show()
This is theoretically fine: all works as expected. But there's a huge problem: the above overwrites self.ui, meaning that we lose all references to the widgets of the main window.
Suppose that you want to set the text of the line edit in the dialog based on the text written in that of the main window; the following will probably crash:
def createWindow(self):
self.window = QDialog()
self.ui = Ui_Dialog()
self.ui.setupUi(self.window)
self.ui.anotherLineEdit.setText(self.ui.myLineEdit.text())
self.window.show()
This clearly shows an important aspect: it's mandatory to always think before assigning attributes that may already exist.
In the code here above, this was actually done twice: not only we overwrote the self.ui we created before, but we also did it for window(), which is an existing function of all Qt widgets (it returns the top level ancestor window of the widget on which it was called).
As a rule of thumb, always take your time to decide how to name objects, use smart names, and consider that most common names are probably already taken: remember to check the "List of all members, including inherited members" link in the documentation of the widget type you're using, until you're experienced enough to remember them.
Solutions
The obvious solution is to use a different name for the ui of the dialog:
def createWindow(self):
self.dialog = QDialog()
self.dialog_ui = Ui_Dialog()
self.dialog_ui.setupUi(self.dialog)
self.dialog_ui.anotherLineEdit.setText(self.ui.myLineEdit.text())
self.dialog.show()
A better solution is to create a subclass for your dialog instead:
class MyDialog(QDialog):
def __init__(self, parent=None)
super().__init__(parent)
self.ui = Ui_Dialog()
self.ui.setupUi(self)
class MyWindow(QMainWindow):
# ...
def createWindow(self):
self.dialog = MyDialog()
self.dialog.ui.anotherLineEdit.setText(self.ui.myLineEdit.text())
self.dialog.show()
Also remember that another common (and, to my experience, simpler and more intuitive) method is to use multiple inheritance instead of composition:
class MyDialog(QDialog, Ui_Dialog):
def __init__(self, parent=None)
super().__init__(parent)
self.setupUi(self)
class MyWindow(QMainWindow, Ui_MainWindow):
def __init__(self):
super().__init__()
self.setupUi(self)
self.myLineEdit.setText('some text')
def createWindow(self):
self.dialog = MyDialog()
self.dialog.anotherLineEdit.setText(self.myLineEdit.text())
self.dialog.show()
The only issue of this approach is that it may inadvertently overwrite names of functions of the "main" widget: for instance, if you created a child widget in Designer and renamed it "window". As said above, if you always think thoroughly about the names you assign to objects, this will probably never happen (it doesn't make a lot of sense to name a widget "window").

What is the advantage of converting a ui file to Python code vs loading it directly? [duplicate]

This question already has answers here:
Benefits of using pyuic vs uic.loadUi
(2 answers)
Closed 1 year ago.
Is there an advantage to:
Converting it to python
pyside6-uic mainwindow.ui > ui_mainwindow.py
and then
import sys
from PySide6.QtWidgets import QApplication, QMainWindow
from PySide6.QtCore import QFile
from ui_mainwindow import Ui_MainWindow
class MainWindow(QMainWindow):
def __init__(self):
super(MainWindow, self).__init__()
self.ui = Ui_MainWindow()
self.ui.setupUi(self)
if __name__ == "__main__":
app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec())
vs. loading it directly like so: ?
ui_file = QFile("mainwindow.ui")
ui_file.open(QFile.ReadOnly)
loader = QUiLoader()
window = loader.load(ui_file)
window.show()
I suppose the app will start faster/run faster if converted beforehand.
Is there anything else to consider?
There are two main differences:
in terms of loading, QUiLoader theoretically adds a bit of overhead because it has to build the ui everytime, meaning that it has to parse the XML file, create the node structure, and then create the UI with all its contents; the uic file, instead, directly creates the UI, skipping the first two steps above;
QUiLoader can only create a new widget based on the UI file, while the uic method allows to use an already existing base widget, and the child widgets can be added to it;
The latter point is probably the most important: using QUiLoader you cannot directly use subclassing for the loaded UI.
For instance, if you create a main window in Designer, QUiLoader will return a new QMainWindow. You cannot (or, at least, you should not) do the following:
class MainWindow(QMainWindow):
def __init__(self):
super(MainWindow, self).__init__()
ui_file = QFile("mainwindow.ui")
ui_file.open(QFile.ReadOnly)
loader = QUiLoader()
window = loader.load(ui_file, self)
And you should not even try to make the returned object as central widget, like the following:
self.setCentralWidget(window)
because the result would be to have a QMainWindow inside a QMainWindow, which is discouraged and unsupported, and might also create problems when using the standard features of a QMainWindow (typically, docks and toolbars).
The only alternative would be to create a basic form widget in Designer and use that as central widget, with the downside that menus, docks and toolbars have to be created by code.
For PySide, the only possibility that allows full subclassing is to use the pyside-uic method and then eventually use the multiple inheritance (but that's not a requirement, as composition is a valid alternative anyway):
class MainWindow(QMainWindow, Ui_MainWindow):
def __init__(self):
super(MainWindow, self).__init__()
self.setupUi(self)
On the other hand, PyQt provides the loadUi function that actually does what setupUi does, since the second argument is not the parent widget, but the widget itself, and the contents of the ui will be loaded into it:
class MainWindow(QMainWindow):
def __init__(self):
super(MainWindow, self).__init__()
uic.loadUi("mainwindow.ui", self)
As far as I know, PySide doesn't provide anything similar yet.
Note that loading the ui at runtime has two issues anyway, and for both bindings:
there is no prior sanity checking, if the UI file is corrupted or invalid, or has unsupported features/properties due to version mismatch, it might not load properly or even crash;
when using an IDE, there's no code completion for ui objects, since they are only loaded at runtime;
Those are not major issues, but it's important to be aware of them anyway.

How to run a pyqt5 application properly?

I can't get the GUI for my application to run in the manner that I need it to. My question is, given the below criteria, how do I go about setting up and running the GUI properly. The lack of good documentation that I have found is insanely frustrating (maybe I'm looking in the wrong places?).
I have a main window in a file called MainCustomerWindow.py containing a class by the same name. This is where all the code from the qt designer is. I have another class file called GUIController. The GUIController class does just that, controls the multiple GUI windows. It is in this GUIController class that I am trying to instantiate and run the MainCustomerWindow. Here is the code I have been trying.
def setup_window(self):
APP = QtWidgets.QApplication(sys.argv)
Window = MainCustomerWindow()
Window.setupUi(QtWidgets.QMainWindow)
Window.show()
sys.exit(APP.exec_())
Just as a side note, I come from JavaFX and Swing, and don't fully understand the workflow for pyqt5. So if someone could add an explanation for that as well it would be greatly appreciated.
The class generated by Qt Designer is not a widget, it is a class used to fill an existing widget, so you must create an object in the window, assuming you have used the "Main Window" template, then the widget must be QMainWindow (if it is another maybe you should use QDialog or QWidget), then you have to create another class that belongs to the design, and using the method setupUi() you must pass the widget to fill it:
def setup_window(self):
app = QtWidgets.QApplication(sys.argv)
# create window
window = QtWidgets.QMainWindow()
ui = MainCustomerWindow()
# fill window
ui.setupUi(window)
window.show()
sys.exit(app.exec_())
Although a better option is to create a new class and have it inherit from both:
class MainWindow(QtWidgets.QMainWindow, MainCustomerWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.setupUi(self)
If you want to get detailed information I recommend you read the following:
http://pyqt.sourceforge.net/Docs/PyQt5/designer.html
You can try taking the code you have there and adding it to the main statement at the end of your app's script. You can also have this statement instantiate your class where the init method contains the setupui() call. For example:
if __name__ == '__main__':
app = QWidgets.QApplication(sys.argv)
window = QMainWindow()
main_window = MainCustomerWindow()
window.show()
sys.exit(app.exec())
This code first sets up the PyQt app as an instance of QApplication. Next it instantiates an instance of QMainWindow so that PyQt knows what to display as the main app starts. In my experience, I've put setupui() in the init method of the app class. In your case, in the init method of MainCustomerWindow Finally, window.show() tells PyQt to begin rendering the main window.

How to get text from lineEdit in Pyside?

I'm learning Pyside and I can't seem to get text from a QLineEdit into my own method so that I can input it into a query etc. I know it has to do with lineEdit.text(), but it isn't seeming to work. Do I need to associate it with a signal before the text will go into my variable??
This is the type of thing I've been trying. Do I need a textChanged signal to get it to update or something?? I've tried adding self.line , but that didn't work either, a little rusty on object oriented programming.
line=QtGui.QLineEdit(self)
myVar = line.text()
A short code example would be great. Thanks!
You seem to be creating the object and using it right afterwards. Of course, you get an empty string from text(); it doesn't work like that.
You should add the QLineEdit to a GUI, let the user do something with it and then obtain the text with QLineEdit.text(). To know when exactly the user changed the text, yes, you should connect to the QLineEdit.textEdited slot.
Here is a full example that uses such a mechanism to copy all the text from a QLineEdit to a QLabel as soon as it's modified.
import sys
from PySide.QtCore import *
from PySide.QtGui import *
class MainWindow(QWidget):
def __init__(self):
QWidget.__init__(self)
layout = QVBoxLayout()
self.setLayout(layout)
self.line_edit = QLineEdit()
layout.addWidget(self.line_edit)
self.label = QLabel()
layout.addWidget(self.label)
self.line_edit.textChanged.connect(self.line_edit_text_changed)
self.show()
def line_edit_text_changed(self, text):
self.label.setText(text)
app = QApplication(sys.argv)
mw = MainWindow()
app.exec_()
This is example shows how you can connect your own function to a slot. But since a QLabel has a setText slot, we could just do self.line_edit.textChanged.connect(self.line_edit.setText) and not define a function.
P.S. You really should read some tutorial; I found this one very useful.

How to detect mouse click on images displayed in GUI created using PySide

Firstly, I'm new to Python, Qt and PySide so forgive me if this question seems too simple.
What I'm trying to do is to display a bunch of photos in a grid in a GUI constructed using PySide API. Further, when a user clicks on a photo, I want to be able to display the information corresponding to that photo. Additionally, I would like the container/widget used for displaying the photo to allow for the photo to be changed e.g. I should be able to replace any photo in the grid without causing the entire grid of photos to be created from scratch again.
Initially I tried to use QLabel to display a QPixmap but I realized (whether mistakenly or not) that I have no way to detect mouse clicks on the label. After some searching, I got the impression that I should subclass QLabel (or some other relevant class) and somehow override QWidget's(QLabel's parent class) mousePressEvent() to enable mouse click detection. Problem is I'm not sure how to do that or whether there is any alternative widget I can use to contain my photos other than the QLabel without having to go through subclass customization.
Can anyone suggest a more suitable container other than QLabel to display photos while allowing me to detect mouse clicks on the photo or provide some code snippet for subclassing QLabel to enable it to detect mouse clicks?
Thanks in advance for any replies.
I've added an example of how to emit a signal and connect to another slot. Also the docs are very helpful
from PySide.QtCore import *
from PySide.QtGui import *
import sys
class Main(QWidget):
def __init__(self, parent=None):
super(Main, self).__init__(parent)
layout = QHBoxLayout(self)
picture = PictureLabel("pic.png", self)
picture.pictureClicked.connect(self.anotherSlot)
layout.addWidget(picture)
layout.addWidget(QLabel("click on the picture"))
def anotherSlot(self, passed):
print passed
print "now I'm in Main.anotherSlot"
class PictureLabel(QLabel):
pictureClicked = Signal(str) # can be other types (list, dict, object...)
def __init__(self, image, parent=None):
super(PictureLabel, self).__init__(parent)
self.setPixmap(image)
def mousePressEvent(self, event):
print "from PictureLabel.mousePressEvent"
self.pictureClicked.emit("emit the signal")
a = QApplication([])
m = Main()
m.show()
sys.exit(a.exec_())
Even if the question has been answered, i want to provide an other way that can be used in different situations (see below) :
from PySide.QtCore import *
from PySide.QtGui import *
import sys
class Main(QWidget):
def __init__(self, parent=None):
super(Main, self).__init__(parent)
layout = QHBoxLayout(self)
picture = QLabel()
picture.setPixmap("pic.png")
layout.addWidget(picture)
layout.addWidget(QLabel("click on the picture"))
makeClickable(picture)
QObject.connect(picture, SIGNAL("clicked()"), self.anotherSlot)
def anotherSlot(self):
print("AnotherSlot has been called")
def makeClickable(widget):
def SendClickSignal(widget, evnt):
widget.emit(SIGNAL('clicked()'))
widget.mousePressEvent = lambda evnt: SendClickSignal(widget, evnt)
a = QApplication([])
m = Main()
m.show()
sys.exit(a.exec_())
This way doesn't imply subclassing QLabel so it can be used to add logic to a widget made with QtDeigner.
Pros :
Can be used over QTdesigner compiled files
Can be applied to any kind of widget (you might need to include a super call to the overrided function to ensure widget's normal behavior)
The same logic can be used to send other signals
Cons :
You have to use the QObject syntax to connect signals and slots

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