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| - | In this part of the PyQt4 programming tutorial, we will explore events and singnals occuring in applications.
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| - | == Events ==
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| - | Events are an important part in any GUI program. Events are generated by users or by the system. When we call the application's <i>exec_()</i> method, the application enters the main loop. The main loop fetches events and sends them to the objects. Trolltech has introduced a unique signal and slot mechanism.
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| - | == Signals & Slots ==
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| - | Signals are emitted, when users click on the button, drag a slider etc. Signals can be emitted also by the environment. For example, when a clock ticks. A slot is a method, that reacts to a signal. In python, a slot can be any python callable.
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| - | <source lang="python">
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| - | #!/usr/bin/python
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| - | # sigslot.py
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| - | import sys
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| - | from PyQt4 import QtGui, QtCore
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| - | class SigSlot(QtGui.QWidget):
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| - | def __init__(self, parent=None):
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| - | QtGui.QWidget.__init__(self, parent)
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| - | self.setWindowTitle('signal & slot')
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| - | lcd = QtGui.QLCDNumber(self)
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| - | slider = QtGui.QSlider(QtCore.Qt.Horizontal, self)
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| - | vbox = QtGui.QVBoxLayout()
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| - | vbox.addWidget(lcd)
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| - | vbox.addWidget(slider)
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| - | self.setLayout(vbox)
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| - | self.connect(slider, QtCore.SIGNAL('valueChanged(int)'), lcd,
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| - | QtCore.SLOT('display(int)') )
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| - | self.resize(250, 150)
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| - | app = QtGui.QApplication(sys.argv)
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| - | qb = SigSlot()
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| - | qb.show()
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| - | sys.exit(app.exec_())
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| - | </source>
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| - | In our example, we display an lcd number and a slider. We change the lcd number by dragging the slider.
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| - | <source lang="python">
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| - | self.connect(slider, QtCore.SIGNAL('valueChanged(int)'), lcd, QtCore.SLOT('display(int)') )
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| - | </source>
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| - | Here we connect a <i>valueChanged()</i> signal of the slider to the <i>display()</i> slot of the lcd number.
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| - | The connect method has four parameters. The <b>sender</b> is an object that sends a signal. The <b>signal</b> is the signal, which is emitted. The <b>receiver</b> is the object, that receives the signal. Finally the <b>slot</b> is the method, that reacts to the signal.
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| - | [[image: pyqt_faq_signalslot.jpg | center]]
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| - | == Reimplementing event handler ==
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| - | Events in PyQt are processed mainly by reimplementing event handlers .
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| - | <source lang="python">
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| - | #!/usr/bin/python
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| - | # escape.py
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| - | import sys
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| - | from PyQt4 import QtGui, QtCore
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| - | class Escape(QtGui.QWidget):
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| - | def __init__(self, parent=None):
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| - | QtGui.QWidget.__init__(self, parent)
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| - | self.setWindowTitle('escape')
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| - | self.resize(250, 150)
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| - | self.connect(self, QtCore.SIGNAL('closeEmitApp()'), QtCore.SLOT('close()') )
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| - | def keyPressEvent(self, event):
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| - | if event.key() == QtCore.Qt.Key_Escape:
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| - | self.close()
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| - | app = QtGui.QApplication(sys.argv)
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| - | qb = Escape()
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| - | qb.show()
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| - | sys.exit(app.exec_())
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| - | </source>
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| - | In our example, we reimplement the <i>keyPressEvent()</i> event handler.
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| - | <source lang="python">
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| - | def keyPressEvent(self, event):
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| - | if event.key() == QtCore.Qt.Key_Escape:
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| - | self.close()
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| - | </source>
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| - | If we click the escape button, we close the application.
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| - | == Emitting signals ==
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| - | Objects created from <i>QtCore.QObject</i> can emit signals.
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| - | If we click on the button, a clicked() signal is generated. In the following example we will see, how we can emit signals.
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| - | <source lang="python">
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| - | #!/usr/bin/python
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| - | # emit.py
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| - | import sys
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| - | from PyQt4 import QtGui, QtCore
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| - | class Emit(QtGui.QWidget):
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| - | def __init__(self, parent=None):
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| - | QtGui.QWidget.__init__(self, parent)
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| - | self.setWindowTitle('emit')
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| - | self.resize(250, 150)
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| - | self.connect(self, QtCore.SIGNAL('closeEmitApp()'), QtCore.SLOT('close()') )
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| - | def mousePressEvent(self, event):
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| - | self.emit(QtCore.SIGNAL('closeEmitApp()'))
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| - | app = QtGui.QApplication(sys.argv)
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| - | qb = Emit()
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| - | qb.show()
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| - | sys.exit(app.exec_())
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| - | </source>
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| - | We create a new signal called <i>closeEmitApp()</i>. This signal is emitted, during a mouse press event.
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| - | <source lang="python">
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| - | def mousePressEvent(self, event):
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| - | self.emit(QtCore.SIGNAL('closeEmitApp()'))
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| - | </source>
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| - | Emitting a signal with the <i>emit()</i> method.
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| - | <source lang="python">
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| - | self.connect(self, QtCore.SIGNAL('closeEmitApp()'), QtCore.SLOT('close()') )
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| - | </source>
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| - | Here we connect the manually created <i>closeEmitApp()</i> signal with the <i>close()</i> slot.
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| - | [[Категория:Qt]]
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| - | [[Категория:Python]]
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