[FIXED] InstallEventFilter for custom class

Issue

I have written small program and would like to installEventFilter for tracking mouse event. Any idea?

#!/usr/bin/env python
import os
import sys
from PySide2.QtCore import Qt, QSize, QRegExp, QFile, QTextStream
from PySide2.QtGui import QKeySequence, QTextCharFormat, QBrush,QColor, QTextDocument, QTextCursor
from PySide2.QtWidgets import (QApplication, QDesktopWidget, QMainWindow,
                               QPlainTextEdit, QGridLayout, QGroupBox,
                               QFormLayout, QHBoxLayout, QLabel, QLineEdit,
                               QMenu, QMenuBar, QPushButton, QMessageBox,
                               QTextEdit, QVBoxLayout, QWidget, QAction)

class BlockWindow():
    def __init__(self, waiver_files, app):
        self.waiver_files = waiver_files
        self.app = app
    
    def create_widget(self): 
        self.create_violation_text()
        self.create_violation_window()
        self.create_text_finder()
        #order matter
        main_layout = QVBoxLayout()
        main_layout.addWidget(self.text_finder)
        main_layout.addWidget(self.create_violation_box)
        return main_layout
       
    
    def create_text_finder(self):
        """
        create text finder which wil search string into document
        """
        self.text_finder = QGroupBox()
        layout = QHBoxLayout()
        label = QLabel()
        label.setText("Keyword:")
        self.line_edit = QLineEdit()
        self.line_edit.setText("Enter your search here")
        push_button = QPushButton("Find")
        layout.addWidget(label)
        layout.addWidget(self.line_edit)
        layout.addWidget(push_button)
        self.text_finder.setLayout(layout)
    
    def create_violation_window(self):
        """
        creating violation window which contain text editor,
        violation type and checkbox
        """
        self.create_violation_box = QGroupBox()
        layout = QGridLayout()
        layout.addWidget(self.plain_textedit, 1, 0, 12, 1)
        layout.setColumnMinimumWidth(0, 10)
        self.create_violation_box.setLayout(layout)
    
    def create_violation_text(self):
        """
        creating main violation window which contain all violations
        """
        self.plain_textedit =  QPlainTextEdit()
        self.plain_textedit.setLineWrapMode(QPlainTextEdit.NoWrap)
        self.plain_textedit.setStyleSheet(
        """QPlainTextEdit {font-size: 14pt;
                           font-family: Courier;}""")
        self.plain_textedit.viewport().installEventFilter(self)
    

class MainWindow(QMainWindow):
    def __init__(self, waiver_files, app):
        super().__init__()
        self.width = 1100
        self.height = 700
        self.waiver_files = waiver_files
        self.app = app
        self.set_main_window()
        
        
    def set_main_window(self):
        """
        Setting main window position
        """
        self.setWindowTitle("GUI %s" %(os.path.abspath(__file__)))
        self.setFixedSize(QSize(self.width, self.height))
        wid = QDesktopWidget() 
        screen_width = wid.screen().frameGeometry().width()
        screen_height = wid.screen().frameGeometry().height()
        self.setGeometry(screen_width/2-self.width/2,
                         screen_height/2-self.height/2, 
                         self.width, self.height)
    
    def create_block(self):
        blk = BlockWindow(self.waiver_files, self.app)
        main_layout = blk.create_widget()
        window = QWidget()
        window.setLayout(main_layout)
        self.setCentralWidget(window)
    
    def eventfilter(self, obj, event):
        print ("hi")

        
if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow(__file__, app)
    window.create_block()
    window.show()
    app.exec_()

Solution

The BlockWindow class is a simple python object, while installEventFilter() expects a QObject.

Right now your class is also completely useless as it's only used to call functions and return an object, then it gets completely deleted.

What you should do instead is to create a subclass of the widget you're going to add, and by doing it you will also get the event filter functionality (since QWidget inherits from QObject).

Note that:

• eventFilter() (with a capitalized "F"!) must always return a bool and it's usually better to always return the result of the base implementation if the event isn't being handled;
• mouse movements can only be tracked when a mouse button has been pressed on the target widget, or when using setMouseTracking(True) (which can be set on the scroll area, not the viewport);

class BlockWindow(QWidget):
    def __init__(self, waiver_files, app):
        super().__init__()
        self.waiver_files = waiver_files
        self.app = app

    def create_widget(self): 
        self.create_violation_text()
        self.create_violation_window()
        self.create_text_finder()
        main_layout = QVBoxLayout(self) # <- note this, equivalent to 
                                        # self.setLayout(main_layout)
        main_layout.addWidget(self.text_finder)
        main_layout.addWidget(self.create_violation_box)

    # ...

    def eventFilter(self, obj, event):
        if event.type() == event.MouseMove:
            print('mouse moving')
        return super().eventFilter(obj, event)

class MainWindow(QMainWindow):
    # ...
    def create_block(self):
        blk = BlockWindow(self.waiver_files, self.app)
        blk.create_widget()
        self.setCentralWidget(blk)

^{Also note that: width() and height() are existing dynamic attributes of all QWidgets, and shall not be overwritten with custom variables; the reference to the application is pointless, as it can (and should) always be get through the static QApplication.instance().}

Answered By - musicamante