PySide——Python图形化界面入门教程(三)

　　　　　　　　　　　　　　 ——使用内建新号和槽

　　　　　　　　　　　　　　——Using Built-In Signals and Slots

上一个教程中，我们学习了如何创建和建立交互widgets，以及将他们布局的两种不同的方法。今天我们继续讨论Python/Qt应用响应用户触发的事件：信号和槽。

当用户执行一个动作——点击按钮，选择组合框的值，在文本框中打字——这个widget就会发出一个信号。这个信号自己什么都不做，它必须和槽连接起来才行。槽是一个接受信号的执行动作的对象。

连接内建PySide/PyQt信号

Qt widgets有许多的内建信号。例如，当QPushButton被点击的时候，它发出它的clicked信号。clicked信号可以被连接到一个拥有槽功能的函数（只是一个概要，需要更多内容去运行）

 1 @Slot()
 2 def clicked_slot():
 3     ''' This is called when the button is clicked. '''
 4     print('Ouch!')
 5  
 6  
 7 # Create the button
 8 btn = QPushButton('Sample')
 9  
10 # Connect its clicked signal to our slot
11 btn.clicked.connect(clicked_slot)

注意@Slot()装饰（decorator）在clicked_slot()的定义上方，尽管它不是严格需要的，但它提示C++ Qt库clicked_slot应该被调用。（更多decorators的信息参见http://www.pythoncentral.io/python-decorators-overview/）我们之后会了解到@Slot宏更多的信息。现在，只要知道按钮被点击时会发出clicked信号，它会调用它连接的函数，这个函数生动的输出“Ouch！”。

我们接下来看看QPushButton发出它的三个相关信号，pressed，released和clicked。

 1 import sys
 2 from PySide.QtCore import Slot
 3 from PySide.QtGui import *
 4  
 5 # ... insert the rest of the imports here
 6 # Imports must precede all others ...
 7  
 8 # Create a Qt app and a window
 9 app = QApplication(sys.argv)
10  
11 win = QWidget()
12 win.setWindowTitle('Test Window')
13  
14 # Create a button in the window
15 btn = QPushButton('Test', win)
16  
17 @Slot()
18 def on_click():
19     ''' Tell when the button is clicked. '''
20     print('clicked')
21  
22 @Slot()
23 def on_press():
24     ''' Tell when the button is pressed. '''
25     print('pressed')
26  
27 @Slot()
28 def on_release():
29     ''' Tell when the button is released. '''
30     print('released')
31  
32 # Connect the signals to the slots
33 btn.clicked.connect(on_click)
34 btn.pressed.connect(on_press)
35 btn.released.connect(on_release)
36  
37 # Show the window and run the app
38 win.show()
39 app.exec_()

当你点击应用的按钮时，它会输出

pressed
released
clicked

pressed信号是按钮被按下时发出，released信号在按钮释放时发出，最后，所有动作完成后，clicked信号被发出。

完成我们的例子程序

现在，很容易完成上一个教程创建的例子程序了。我们为LayoutExample类添加一个显示问候信息的槽方法。

@Slot()
def show_greeting(self):
    self.greeting.setText('%s, %s!' %
                          (self.salutations[self.salutation.currentIndex()],
                          self.recipient.text()))

 我们使用recipient QLineEdit的text()方法来取回用户输入的文本，salutation QComboBox的currentIndex()方法获得用户的选择。这里同样使用Slot()修饰符来表明show_greeting将被作为槽来使用。然后，我们将按钮的clicked信号与之连接：

self.build_button.clicked.connect(self.show_greeting)

最后，例子像是这样：

 1 import sys
 2 from PySide.QtCore import Slot
 3 from PySide.QtGui import *
 4  
 5 # Every Qt application must have one and only one QApplication object;
 6 # it receives the command line arguments passed to the script, as they
 7 # can be used to customize the application's appearance and behavior
 8 qt_app = QApplication(sys.argv)
 9  
10 class LayoutExample(QWidget):
11     ''' An example of PySide absolute positioning; the main window
12         inherits from QWidget, a convenient widget for an empty window. '''
13  
14     def __init__(self):
15         # Initialize the object as a QWidget and
16         # set its title and minimum width
17         QWidget.__init__(self)
18         self.setWindowTitle('Dynamic Greeter')
19         self.setMinimumWidth(400)
20  
21         # Create the QVBoxLayout that lays out the whole form
22         self.layout = QVBoxLayout()
23  
24         # Create the form layout that manages the labeled controls
25         self.form_layout = QFormLayout()
26  
27         self.salutations = ['Ahoy',
28                             'Good day',
29                             'Hello',
30                             'Heyo',
31                             'Hi',
32                             'Salutations',
33                             'Wassup',
34                             'Yo']
35  
36         # Create and fill the combo box to choose the salutation
37         self.salutation = QComboBox(self)
38         self.salutation.addItems(self.salutations)
39         # Add it to the form layout with a label
40         self.form_layout.addRow('&Salutation:', self.salutation)
41  
42         # Create the entry control to specify a
43         # recipient and set its placeholder text
44         self.recipient = QLineEdit(self)
45         self.recipient.setPlaceholderText("e.g. 'world' or 'Matey'")
46  
47         # Add it to the form layout with a label
48         self.form_layout.addRow('&Recipient:', self.recipient)
49  
50         # Create and add the label to show the greeting text
51         self.greeting = QLabel('', self)
52         self.form_layout.addRow('Greeting:', self.greeting)
53  
54         # Add the form layout to the main VBox layout
55         self.layout.addLayout(self.form_layout)
56  
57         # Add stretch to separate the form layout from the button
58         self.layout.addStretch(1)
59  
60         # Create a horizontal box layout to hold the button
61         self.button_box = QHBoxLayout()
62  
63         # Add stretch to push the button to the far right
64         self.button_box.addStretch(1)
65  
66         # Create the build button with its caption
67         self.build_button = QPushButton('&Build Greeting', self)
68  
69         # Connect the button's clicked signal to show_greeting
70         self.build_button.clicked.connect(self.show_greeting)
71  
72         # Add it to the button box
73         self.button_box.addWidget(self.build_button)
74  
75         # Add the button box to the bottom of the main VBox layout
76         self.layout.addLayout(self.button_box)
77  
78         # Set the VBox layout as the window's main layout
79         self.setLayout(self.layout)
80  
81     @Slot()
82     def show_greeting(self):
83         ''' Show the constructed greeting. '''
84         self.greeting.setText('%s, %s!' %
85                               (self.salutations[self.salutation.currentIndex()],
86                                self.recipient.text()))
87  
88     def run(self):
89         # Show the form
90         self.show()
91         # Run the qt application
92         qt_app.exec_()
93  
94 # Create an instance of the application window and run it
95 app = LayoutExample()
96 app.run()

View Code

运行它你会发现点击按钮可以产生问候信息了。现在我们知道了如何使用我们创建的槽去连接内建的信号，下一个教程中，我们将学习创建并连接自己的信号。

By Ascii0x03

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