PyQt -- Signals and Slots

接下來這個範例，主要是介紹Qt獨特有的Signals and Slots的技術，PyQt本身也有繼承這個高階的呼叫方式，所以需要特別介紹一下：

#!/usr/bin/env python
# Copyright (c) 2007-8 Qtrac Ltd. All rights reserved.
# This program or module is free software: you can redistribute it and/or
# modify it under the terms of the GNU General Public License as published
# by the Free Software Foundation, either version 2 of the License, or
# version 3 of the License, or (at your option) any later version. It is
# provided for educational purposes and is distributed in the hope that
# it will be useful, but WITHOUT ANY WARRANTY; without even the implied
# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
# the GNU General Public License for more details.

import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *

class Form(QDialog):

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

      dial = QDial()
      dial.setNotchesVisible(True)
      spinbox = QSpinBox()

      layout = QHBoxLayout()
      layout.addWidget(dial)
      layout.addWidget(spinbox)
      self.setLayout(layout)

      self.connect(dial, SIGNAL("valueChanged(int)"),
                   spinbox.setValue)
      self.connect(spinbox, SIGNAL("valueChanged(int)"),
                   dial.setValue)
      self.setWindowTitle("Signals and Slots")


class Form2(QDialog):

  def __init__(self, parent=None):
      super(Form2, self).__init__(parent)

      dial = QDial()
      dial.setNotchesVisible(True)
      spinbox = QSpinBox()

      layout = QHBoxLayout()
      layout.addWidget(dial)
      layout.addWidget(spinbox)
      self.setLayout(layout)

      self.connect(dial, SIGNAL("valueChanged(int)"),
                   spinbox, SLOT("setValue(int)"))
      self.connect(spinbox, SIGNAL("valueChanged(int)"),
                   dial, SLOT("setValue(int)"))
      self.setWindowTitle("Signals and Slots")


class ZeroSpinBox(QSpinBox):

  zeros = 0

  def __init__(self, parent=None):
      super(ZeroSpinBox, self).__init__(parent)
      self.connect(self, SIGNAL("valueChanged(int)"), self.checkzero)


  def checkzero(self):
      if self.value() == 0:
          self.zeros += 1
          self.emit(SIGNAL("atzero"), self.zeros)


class Form3(QDialog):

  def __init__(self, parent=None):
      super(Form3, self).__init__(parent)

      dial = QDial()
      dial.setNotchesVisible(True)
      zerospinbox = ZeroSpinBox()

      layout = QHBoxLayout()
      layout.addWidget(dial)
      layout.addWidget(zerospinbox)
      self.setLayout(layout)

      self.connect(dial, SIGNAL("valueChanged(int)"),
                   zerospinbox, SLOT("setValue(int)"))
      self.connect(zerospinbox, SIGNAL("valueChanged(int)"),
                   dial, SLOT("setValue(int)"))
      self.connect(zerospinbox, SIGNAL("atzero"), self.announce)
      self.setWindowTitle("Signals and Slots")


  def announce(self, zeros):
      print "ZeroSpinBox has been at zero %d times" % zeros


class Form4(QDialog):

  def __init__(self, parent=None):
      super(Form4, self).__init__(parent)

      lineedit = QLineEdit()

      layout = QHBoxLayout()
      layout.addWidget(lineedit)
      self.setLayout(layout)

      self.connect(lineedit, SIGNAL("textChanged(QString)"),
                   self.consoleEcho)
      self.setWindowTitle("Signals and Slots")


  def consoleEcho(self, text):
      print unicode(text)
    


class TaxRate(QObject):

  def __init__(self):
      super(TaxRate, self).__init__()
      self.__rate = 17.5


  def rate(self):
      return self.__rate


  def setRate(self, rate):
      if rate != self.__rate:
          self.__rate = rate
          self.emit(SIGNAL("rateChanged"), self.__rate)


def rateChanged(value):
  print "TaxRate changed to %.2f%%" % value


app = QApplication(sys.argv)
form = None
if len(sys.argv) == 1 or sys.argv[1] == "1":
  form = Form()
elif sys.argv[1] == "2":
  form = Form2()
elif sys.argv[1] == "3":
  form = Form3()
elif sys.argv[1] == "4":
  form = Form4()
if form is not None:
  form.show()
  app.exec_()
else: # if sys.argv[1] == "5"
  vat = TaxRate()
  vat.connect(vat, SIGNAL("rateChanged"), rateChanged)
  vat.setRate(17.5)    # No change will occur (new rate is the same)
  vat.setRate(8.5)     # A change will occur (new rate is different)

要注意,這個範例裡面使用了QDial與QSpinBox兩個Widget. 這兩個Widget都有用到valueChanged()這個signal. 而且也是利用了這個signal來交換資訊。當QDial透過SIGNAL("ValueChanged(int)")接受到數值改變的指令後,就用setValue(int)去告知QspinBox; 反之亦然. 所以當你改變任何一邊的數值時, 另外一邊的也隨之變化.