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= Events and Signals in PyQt4 =
'''PyQt4中的事件和信号'''

'' In this part of the PyQt4 programming tutorial, we will explore events and singnals occuring in applications.''

 . 在PyQt4编程指导的这一部分，我们将探索事件和信号在程序里的存在。

== Events ==
'''事件'''

'' Events are an important part in any GUI program. Events are generated by users or by the system. When we call the application's exec_() 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.''

 . 事件是任何GUI程序中最重要的部分。事件由用户或者系统生成，当我们调用应用程序的exec_()方法时，应用程序进入了它的主循环，主循环获取事件并将他们送给对象处理。奇趣科技引入了一种独一无二的信号和插槽机制来处理事件。

== Signals & Slots ==
'''信号和插槽'''

''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. ''

 . 当用户点击按钮，拖动滑块等操作时会产生信号，同时环境也可以产生信号，比如时钟的信号。插槽是一种针对信号进行处理的方法。python中插槽可以是任何的python可调用部分。

{{{
#!python
#!/usr/bin/python
# sigslot.py
import sys
from PyQt4 import QtGui, QtCore
class SigSlot(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.setWindowTitle('signal & slot')
        lcd = QtGui.QLCDNumber(self)
        slider = QtGui.QSlider(QtCore.Qt.Horizontal, self)
        vbox = QtGui.QVBoxLayout()
        vbox.addWidget(lcd)
        vbox.addWidget(slider)
        self.setLayout(vbox)
        self.connect(slider,  QtCore.SIGNAL('valueChanged(int)'), lcd,
                QtCore.SLOT('display(int)') )
        self.resize(250, 150)
app = QtGui.QApplication(sys.argv)
qb = SigSlot()
qb.show()
sys.exit(app.exec_())
}}}
'' In our example, we display an lcd number and a slider. We change the lcd number by dragging the slider. ''

 . 在这个例子中，我们显示一个lcd数字和一个滑块，我们可以通过拖拽滑块来改变lcs的数字显示。

{{{
 self.connect(slider,  QtCore.SIGNAL('valueChanged(int)'), lcd, QtCore.SLOT('display(int)') )
}}}
'' Here we connect a valueChanged() signal of the slider to the display() slot of the lcd number.''

 . 这里我们将滑块的valueChanged()信号与lcd数字的display()插槽相关联。

'' The connect method has four parameters. The sender is an object that sends a signal. The signal is the signal, which is emitted. The receiver is the object, that receives the signal. Finally the slot is the method, that reacts to the signal.''

 . 连接方法有四个参数。sender是发送信号的对象，signal是它产生的信号，receiver是接收信号的对象，最后的slot是相应信号的方法。

 . signals & slots
Figure: signal & slot

== Reimplementing event handler ==
'''事件处理重载'''

'' Events in PyQt are processed mainly by reimplementing event handlers .''

 . PyQt中的事件处理主要是通过对事件处理者的重载来进行的。

{{{
#!python
#!/usr/bin/python
# escape.py
import sys
from PyQt4 import QtGui, QtCore
class Escape(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.setWindowTitle('escape')
        self.resize(250, 150)
        self.connect(self, QtCore.SIGNAL('closeEmitApp()'), QtCore.SLOT('close()') )
    def keyPressEvent(self, event):
        if event.key() == QtCore.Qt.Key_Escape:
            self.close()
app = QtGui.QApplication(sys.argv)
qb = Escape()
qb.show()
sys.exit(app.exec_())
}}}
'' In our example, we reimplement the keyPressEvent() event handler.''

 . 在这个例子里，我们重载了keyPressEvent()方法。

{{{
 def keyPressEvent(self, event):
     if event.key() == QtCore.Qt.Key_Escape:
         self.close()
}}}
'' If we click the escape button, we close the application.''

 . 如果我们按下ESC键，程序将关闭。

== Emitting signals ==
发送信号

'' Objects created from QtCore.QObject can emit signals. If we click on the button, a clicked() signal is generated. In the following example we will see, how we can emit signals.''

 . 通过QtCore.QObject创建的对象可以发送信号。如果我们点击按钮，就会生成一个clicked()信号。在以下的例子里我们会看到如何发送一个信号。

{{{
#!python
#!/usr/bin/python
# emit.py
import sys
from PyQt4 import QtGui, QtCore
class Emit(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.setWindowTitle('emit')
        self.resize(250, 150)
        self.connect(self, QtCore.SIGNAL('closeEmitApp()'), QtCore.SLOT('close()') )
    def mousePressEvent(self, event):
        self.emit(QtCore.SIGNAL('closeEmitApp()'))
app = QtGui.QApplication(sys.argv)
qb = Emit()
qb.show()
sys.exit(app.exec_())
}}}
'' We create a new signal called closeEmitApp(). This signal is emitted, during a mouse press event. ''

 . 我们创建一个叫做closeEmitApp()的新的信号。这个信号在鼠标按下时产生。

{{{
 def mousePressEvent(self, event):
     self.emit(QtCore.SIGNAL('closeEmitApp()'))
}}}
'' Emitting a signal with the emit() method.''

 . 通过emit()来产生一个信号。

{{{
 self.connect(self, QtCore.SIGNAL('closeEmitApp()'), QtCore.SLOT('close()') )
}}}
'' Here we connect the manually created closeEmitApp() signal with the close() slot.''

 . 这里我们将我们手工产生的closeEmitApp()信号与close()插槽连接。