# A demo of how to get notifications that the state of a checkbox has
# changed as well as echoing the change using a QTextEdit. This demo
# also shows how to change the size of the Dialog.
  
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
  
import sys
import os
import math
  
class Demo_QCheckbox_QTextEdit(QDialog):
    def __init__(self, parent=None):
        QDialog.__init__(self, parent)
  
        self.setWindowFlags(Qt.WindowStaysOnTopHint)
        self.setWindowTitle("Demo QCheckbox - Show/Hide QTextEdit")
        self.setFixedSize(450, 100)
        
        # Create and set the main vertical layout.
        vlayout = QVBoxLayout()
        self.setLayout(vlayout)    
        
        self.addCheckboxPanel(vlayout)
        self.addTextEditPanel(vlayout) # initially hidden
        
        # Ensure the two panels are pushed to the upper edge of the
        # Dialog window.
        vlayout.addStretch()    
            
        self.show()
        
    #--------------------------------------------------------------    
    def addTextEditPanel(self, parentLayout):
        self.textEdit = QTextEdit(self)
        self.textEdit.setReadOnly(True)
        self.textEdit.setLineWrapMode(QTextEdit.NoWrap)
        self.textEdit.resize(400,400)
        self.textEdit.setVisible(False)
        
        font = self.textEdit.font()
        font.setFamily("Courier")
        font.setPointSize(10)
        parentLayout.addWidget(self.textEdit)
    #--------------------------------------------------------------        
    def addCheckboxPanel(self, parentLayout):
        hlayout = QHBoxLayout()
        checkbox = QCheckBox('Show TextEdit')
        checkbox.stateChanged.connect(self.chechboxAction)
        hlayout.addWidget(checkbox)
        hlayout.addStretch()
        parentLayout.addLayout(hlayout)
            
    #--------------------------------------------------------------
    # Activated by user selecting or deselecting the checkbox.
    def chechboxAction(self):
        cb = self.sender()
        if cb.isChecked():
            self.textEdit.setVisible(True)
            self.setFixedSize(450, 300)
            self.textEdit.resize(400,200)
            self.textEdit.append('Checkbox has been selected')
        else:
            self.textEdit.setVisible(False)
            self.setFixedSize(450, 100)
            self.textEdit.append('Checkbox has been deselected\n')
  
# ========================================================                
if __name__ == '__main__':
    # Create the Qt Application
    app = QApplication(sys.argv)
    demo = Demo_QCheckbox_QTextEdit() # <<-- Create an instance
    demo.show()
    sys.exit(app.exec_())