The Only Qt Template You'll Ever Need

qt

General

Template

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class Window(QtWidgets.QMainWindow):

    def __init__(self, parent=None):
        super(Window, self).__init__(parent)

        self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
        self.setWindowFlags(self.windowFlags() | QtCore.Qt.WindowStaysOnTopHint)
        _loadUi(UI_PATH, self)

Import Qt Modules

if you are using PyQt5 binding:

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from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.uic import loadUi

if you are using PySide2 binding, here’s a wrapper I made which can be found here.

I’m using Qt.py a Python 2 & 3 shim around all Qt bindings, it just saves a lot of work.

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from Qt import QtCore, QtGui, QtWidgets
from Qt import _loadUi

Using QApplication

Launch as standalone application using QApplication, or if a QApplication instance exist, there’s no need to instantiate it. use QtWidgets.QApplication.instance() to check

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if __name__ == '__main__':
    import sys
    if QtWidgets.QApplication.instance():
        window = ToolWindow()
        window.show()
    else:
        app = QtWidgets.QApplication(sys.argv)
        window = ToolWindow()
        window.show()
        sys.exit(app.exec_())

Close Event

Delete Widget when Closed

by default, closing the widget is hiding it not destroying the object

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{WindowObject}.setAttribute(QtCore.Qt.WA_DeleteOnClose)

Unique Instance

Raise existing instance (for example: widgets that are hidden during closeEvent); if no instance is available, create a new one.

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def show():
    global WINDOW

    exists = WINDOW is not None
    if not exists:
        WINDOW = ToolWindow()

    WINDOW.showNormal()

Other

Register Style Sheet

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def show():
    ...
    APP = QtWidgets.QApplication(sys.argv)
    with open(PATH_TO_STYLESHEET, 'r') as f:
        qss = f.read()
        APP.setStyleSheet(qss)

Register QResources

QtCore.QResource.registerResource(PATH_TO_RCC)

Maya

Parent to Maya’s Main Window

by default Qt window is not parented to Maya application

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from shiboken2 import wrapInstance


def get_maya_main_window():
    import maya.OpenMayaUI
    main_window_ptr = maya.OpenMayaUI.MQtUtil.mainWindow()
    return wrapInstance(long(main_window_ptr), QtWidgets.QMainWindow)


class ModuleUI(QtWidgets.QMainWindow):
    def __init__(self, parent=get_maya_main_window()):
        super(ModuleUI, self).__init__(parent)
        _loadUi(UI_PATH, self)

Window Docking

Dockable Window

The widget/window can now be docked into Maya’s main window;

Auto-docking

The above example of auto-docking may not work for certain Maya builds

A workaround is to use the following method, but it only applies to QWidget type not QMainWindow type.

Instantiate Widget

When the UI has no parent (Maya main window), it will get instantly destroyed by the garbage collector, unless we keep an instance:

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# in the show function
def show():
    window = ModuleUI()
    window.show()
    return window

# in maya script editor
win = moduleName.show()

or using global variable to store the instance

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def show():
    global window
    window = ModuleUI()
    window.show()

# in maya script editor
moduleName.show()

Close Application in Maya

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def show():
    if cmds.window('xxx', q=1, exists=1):
        cmds.deleteUI('xxx')
    global window
    window = somethingWindow()
    window.setObjectName('xxx')
    window.show()

Error in PyCharm

When this error occurs, it is due to MayaDevKit environment MayaDevKit allows maya python command auto-completion, remove it from PyCharm

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app = QtWidgets.QApplication(sys.argv)
TypeError: 'NoneType' object is not callable

Unreal Engine

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import unreal

def show():
    global app
    global window

    app = QtWidgets.QApplication.instance() or QtWidgets.QApplication(sys.argv)

    window = TestWindow()
    window.show()  # this needs to happen before parenting
    unreal.parent_external_window_to_slate(int(window.winId()))

Raise Existing Instance

in the show() we need to return the window instance and assign it to a global variable:

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# main.py
def show():
    ...
    window.show()
    return window

in the parent python command call (this maybe an Unreal menu command)

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from test import main
global editor
editor = main.show()

Override closeEvent()

To exit the Unreal Editor when Qt Window is closed:

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def closeEvent(self, event):
    QtWidgets.QMainWindow.closeEvent(event)
    unreal.SystemLibrary.execute_console_command(None, "QUIT_EDITOR")

To override at an instance level:

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import types

if __name__ == "__main__":
    def _close_event(self, event):
        QtWidgets.QMainWindow.closeEvent(event)
        unreal.SystemLibrary.execute_console_command(None, "QUIT_EDITOR")

    win = Window()
    win.closeEvent = types.MethodType(_close_event, win)

Bonus:

PySide2 UI Loading

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from PySide2 import QtCore, QtWidgets
from PySide2.QtUiTools import QUiLoader

class WrapperWindow(QtWidgets.QMainWindow):
    ui = ''
    
    def __init__(self, parent=None):
        super(WrapperWindow, self).__init__(parent)

        loader = QUiLoader()
        _file = QtCore.QFile(self.ui)
        _file.open(QtCore.QFile.ReadOnly)
        self.widget = loader.load(_file, parent)
        _file.close()

        self.setCentralWidget(self.widget)


class Window(WrapperWindow):
    ui = 'PATH_TO_UI_FILE'
    
    def __init__(self, parent=None):
        super(Window, self).__init__(parent)
        
        self.setCentralWidget(self.widget)

        # now we can access ui element like so
        self.widget.uiBtn.clicked.connect(self.someFunc)

Reference

Reddit - PyQt5 - Why do I get an Empty Window?

Stack Overflow - pycharm use pyside2 TypeError: ‘NoneType’ object is not callable

Xingyu LeiTechnical Artist

Problem solver; Game and film enthusiast;