This is based on Qt Tutorial #1-7
One Thing Leads to Another
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
'''
PyQt4 conversion of Qt Tutorial 7
The example demonstrates chaining signals so they are propagated
from one widget to another.
BEHAVIOUR:
=========
The application displays 16 LCDRange widgets all set to zero
as in 6_buildingblocks.pyw; however, they no longer act
independently.
Move the slider on the bottom-right widget and see the values
of all the widgets change. Move the slider on the 8th
widget and the values of widgets 1 thru 8 change.
NOTES:
=====
The original example uses two files: lcdrange.cpp and main.cpp
Here they are combined into one module.
The original C++ code connects the slider valueChanged
signal to itself; this is not necessary in PyQt4 and will produce
a "cannot connect a signal to itself" compile error if attempted.
The original code also included a 'value()' method; it was not
being called and so has not been included in this example.
Demonstrates the use of the 'pyqtSlot' decorator which, according to PyQt
documentation, reduces memory usage.
last modified: 2012-01-19 jg
ref:
http://doc.trolltech.com/3.3/tutorial1-07.html
http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/new_style_signals_slots.html
'''
import sys
from PyQt4.QtGui import (QApplication, QWidget, QPushButton, QFont,
QVBoxLayout, QGridLayout, QLCDNumber, QSlider)
from PyQt4.QtCore import (Qt, pyqtSlot)
class LCDRange(QWidget):
'''
A two digit QLCDNumber and QSlider widget.
'''
def __init__(self, parent=None):
super(LCDRange, self).__init__(parent)
# local variable, not directly called by
# external methods
lcd = QLCDNumber(2, self);
# 'slider' defined as an 'attribute'
# as it must be accessed by the 'setValue()' method
self.slider = QSlider(Qt.Horizontal, self);
self.slider.setRange(0, 99);
self.slider.setValue(0);
self.slider.valueChanged.connect(lcd.display)
layout = QVBoxLayout()
layout.addWidget(lcd)
layout.addWidget(self.slider)
self.setLayout(layout)
# a PyQt defined 'slot'
# sets the value of the slider which automatically
# results in a 'valueChanged' signal being sent
@pyqtSlot(int)
def setValue(self, value):
self.slider.setValue(value)
class MyWidget(QWidget):
def __init__(self, parent=None, name=''):
super(MyWidget, self).__init__(parent)
if name:
self.setObjectName(name)
quitBtn = QPushButton('Quit', self)
quitBtn.setFont(QFont("Times", 18, QFont.Bold))
quitBtn.clicked.connect(QApplication.instance().quit)
grid = QGridLayout()
previous = None
for r in range(4):
for c in range(4):
lr = LCDRange(self)
grid.addWidget(lr, r, c)
if previous:
# connect to the 'setValue()' method of the
# previous LCDRange widget; triggering a
# 'valueChanged' signal that is then propagated
# to all 'previously' created LCDRange widgets
lr.slider.valueChanged.connect(previous.setValue)
previous = lr
# nesting layouts
vbox = QVBoxLayout()
vbox.addLayout(grid)
vbox.addWidget(quitBtn)
self.setLayout(vbox)
def main():
app = QApplication(sys.argv) # required
w = MyWidget(name='signalChain')
w.show()
sys.exit(app.exec_()) # start main event loop, exit when app closed
if __name__ == '__main__':
main()
