EventFilter installEventFilter

# -*- coding: utf-8 -*-
"""
Author: Virgil
Date: 2020/6/6 15:09
"""

from PySide2 import QtCore
from PySide2 import QtGui
from PySide2 import QtWidgets
from shiboken2 import wrapInstance

import maya.OpenMayaUI as omui
import maya.cmds as cmds
import maya.mel as mel

def maya_main_window():
    """
    Return the Maya main window widget as a Python object
    """
    main_window_ptr = omui.MQtUtil.mainWindow()
    return wrapInstance(long(main_window_ptr), QtWidgets.QWidget)

class EventFilteringExample(QtWidgets.QDialog):
    WINDOW_TITLE = "Event Filtering Example"

    def __init__(self, parent=maya_main_window()):
        super(EventFilteringExample, self).__init__(parent)

        self.setWindowTitle(self.WINDOW_TITLE)
        self.setMinimumSize(600, 400)

        self.create_widgets()
        self.create_layout()
        self.create_connections()

        self.main_window = maya_main_window()
        self.main_window.installEventFilter(self)

        self.line_edit.installEventFilter(self)

    def create_widgets(self):
        self.line_edit = QtWidgets.QLineEdit()
        self.combo_box = QtWidgets.QComboBox()
        self.combo_box.addItems(["High", "Medium", "Low"])

    def create_layout(self):
        main_layout = QtWidgets.QFormLayout(self)
        main_layout.setContentsMargins(5, 5, 5, 5)

        main_layout.addRow("Name:", self.line_edit)
        main_layout.addRow("Quality:", self.combo_box)

    def create_connections(self):
        pass

    def eventFilter(self, obj, event):
        if obj == self.main_window:
            if self.isVisible():
                if event.type() == QtCore.QEvent.Close:
                    result = QtWidgets.QMessageBox.question(self, "Confirm Close", "Are you sure you want to close?")
                    if result == QtWidgets.QMessageBox.No:
                        event.ignore()
                        return True
        elif obj == self.line_edit:
            if event.type() == QtCore.QEvent.KeyPress:
                if event.key() == QtCore.Qt.Key_A:
                    print("Invalid key press")
                    return True
            elif event.type() == QtCore.QEvent.FocusIn:
                print("Line Eidt gained focus")
            elif event.type() == QtCore.QEvent.FocusOut:
                print("Line Eidt lost focus")


        return False

def showWindow():
    global dialog
    try:
        dialog.close()
        dialog.deleteLater()
    except:
        pass

    dialog = EventFilteringExample()
    dialog.show()

if __name__ == "__main__":
    try:
        dialog.close()
        dialog.deleteLater()
    except:
        pass

    dialog = EventFilteringExample()
    dialog.show()