PyQt5学习笔记(05)--Event and signals

本文代码来自zetcode.com

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Events

GUI应用是以事件驱动，事件的产生主要靠用户。
但是事件也可以通过例如互联网链接、窗口管理器或者计时器产生。
当我们通过exec_()方法进入程序主循环，主循环获取事件后并将其发送。

在事件模型中，有三个参与者：

event source
event object
event target

event source 状态发生改变时产生事件
event object 在事件源中封装改变的状态
event target 事件目标是想要通知的对象

PyQt5具有特有的信号和插槽机制来处理事件：
当事件发生会产生一个 signal，当连接信号发送时，slot被调用。

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Signals and slots

#!/usr/bin/python3

"""
This program will create a signal
of a QSlider to a slot of a QLCDNumber
"""

import sys
from PyQt5.QtWidgets import QWidget, QApplication, QLCDNumber, QSlider, QVBoxLayout
from PyQt5.QtCore import Qt


class Example(QWidget):

    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        lcd = QLCDNumber(self)
        sld = QSlider(Qt.Horizontal, self)

        vbox = QVBoxLayout()
        vbox.addWidget(lcd)
        vbox.addWidget(sld)

        self.setLayout(vbox)
        sld.valueChanged.connect(lcd.display)

        self.setGeometry(300, 300, 250, 150)
        self.setWindowTitle('Signal and slot')
        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

上述代码展示了QtGui.QLCDNumber和QtGui.QSlider，当我们拖拽滑块数字也随之改变。

sld.valueChanged.connect(lcd.display)

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Reimplementing event handler

以下代码实现Esc键退出程序

#!/usr/bin/python3

"""
In this example, we reimplement an event handler.
"""

import sys
from PyQt5.QtWidgets import QWidget, QApplication
from PyQt5.QtCore import Qt


class Example(QWidget):

    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.setGeometry(300, 300, 250, 150)
        self.setWindowTitle('Event Handler')
        self.show()

    def keyPressEvent(self, e):
        if e.key() == Qt.Kye_Escape:
            self.close()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

我们重新实现keyPressEvent()事件处理程序

    def keyPressEvent(self, e):
        if e.key() == Qt.Key_Escape:
            self.close()

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Event object

事件对象是包含许多描述事件的属性，事件对象特定于生成的事件类型。
本例实现移动鼠标展示其所在坐标位置

#!/usr/bin/python3

"""
In this example, we display the x and y
coordinates of a mouse pointer in a label widget.
"""

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QWidget, QApplication, QGridLayout, QLabel


class Example(QWidget):

    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        grid = QGridLayout()

        x = 0
        y = 0

        self.text = "x: {0}, y: {1}".format(x, y)
        self.label = QLabel(self.text, self)    #  (x,y)坐标在QLabel控件中显示

        grid.addWidget(self.label, 0, 0, Qt.AlignTop)    #  将控件放于左上角
        self.setMouseTracking(True)    #  默认为关闭，开启后事件产生信号
        self.setLayout(grid)

        self.setGeometry(300, 300, 350, 200)
        self.setWindowTitle('Event Object')
        self.show()

    def mouseMoveEvent(self, e):
        x = e.x()
        y = e.y()
        text = "x: {0}. y: {1}".format(x, y)
        self.label.setText(text)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

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Event sender

sender()方法可以知道哪个控件发送信号

#!/usr/bin/python3

"""
In this example, we determine the event sender object.
"""

import sys
from PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication


class Example(QMainWindow):

    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):

        btn1 = QPushButton("Button 1", self)
        btn1.move(30, 50)

        btn2 = QPushButton("Button 2", self)
        btn2.move(150, 50)

        btn1.clicked.connect(self.buttonClicked)
        btn2.clicked.connect(self.buttonClicked)

        self.statusBar()

        self.setGeometry(300, 300, 290, 150)
        self.setWindowTitle('Event sender')
        self.show()

    def buttonClicked(self):
        sender = self.sender()
        self.statusBar().showMessage(sender.text() + ' was pressed')


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

本例中显示了两个按钮，当1或2被按下，状态栏会显示提示消息。

sender = self.sender()

通过sender()来知晓信号源

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Emitting signals

从QObject创建的对象可以发送信号

#!/usr/bin/python3

"""
In this example, we show how to emit a custom signal.
"""

import sys
from PyQt5.QtCore import pyqtSignal, QObject
from PyQt5.QtWidgets import QMainWindow, QApplication


class Communicate(QObject):
    closeApp = pyqtSignal()


class Example(QMainWindow):

    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.c = Communicate()
        self.c.closeApp.connect(self.close)

        self.setGeometry(300, 300, 300, 150)
        self.setWindowTitle('Emit Signal')
        self.show()

    def mousePressEvent(self, event):
        self.c.closeApp.emit()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

信号通过pyqtSignal()创建，自定义的closeApp信号连接到QMainWindow的close()插槽。

        self.c = Communicate()
        self.c.closeApp.connect(self.close)

我们定义了鼠标点击事件，当我们点击鼠标时，程序退出

    def mousePressEvent(self, event):
        self.c.closeApp.emit()