Call a function from another class by clicking a button PyQt4

Question

I have a checkbox and a run button. When the checkbox is checked, I want to run some functions by clicking the button. The problem is that the function is in another class outside the button's class. My example codes are as below.

import sys

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

class Tab1Widget1(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)

        self.Tab1Widget1initUI()

    def Tab1Widget1initUI(self):
        self.setLayout(QGridLayout())

        self.T1W1checkBox1 = QCheckBox('a', self)

        self.layout().addWidget(self.T1W1checkBox1, 1, 0)

    def run(self):
        if self.T1W1checkBox1.isChecked() == True:
            pass

class Tab1Layout(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setLayout(QGridLayout())

        self.group1 = Tab1Widget1(self)
        self.layout().addWidget(self.group1, 0, 0)

        btn = QPushButton('Run', self)
        self.layout().addWidget(btn, 1, 0)
        btn.clicked.connect(Tab1Widget1().run())  ##the problem is in this line.

class Page1(QTabWidget):
    def __init__(self, parent=None):
        super(Page1, self).__init__(parent)
        self.tab1 = Tab1Layout()
        self.addTab(self.tab1, "Tab1")

        self.tab2 = QWidget()
        self.tab3 = QWidget()
        self.addTab(self.tab2, "Tab2")
        self.addTab(self.tab3, "Tab3")
        self.tab2_initUI()
        self.tab3_initUI()

    def tab2_initUI(self):
        grid = QGridLayout()
        self.tab2.setLayout(grid)

    def tab3_initUI(self):
        grid = QGridLayout()
        self.tab3.setLayout(grid)

class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setGeometry(300, 200, 600, 370)
        self.startPage1()

    def startPage1(self):
        x = Page1(self)
        self.setWindowTitle("Auto Benchmark")
        self.setCentralWidget(x)
        self.show()

def main():
    app = QApplication(sys.argv)
    main = MainWindow()
    main.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

As you can see, I want to run the "run" function in "Tab1Widget1" class. However, the button is in "Tab1Layout" class. When I run the codes, it returns to me "TypeError: connect() slot argument should be a callable or a signal, not 'NoneType'"

If anyone knows how to solve this, pls let me know. Appreciated!

Answer 1

There is no problem in connecting any callable to a button click regardless of what object it is in. But your code has two specific problems. You write

 btn.clicked.connect(Tab1Widget1().run())  

The first problem here is that Tab1Widget1() is creating a new Tab1Widget1 but presumably you don't want that. You want to call run on the Tab1Widget1 you have already created and stored in self.group.

The second problem is that when you connect a signal you need to connect it to a callable: the method you want to call. Instead here you are calling the run method at connect time and trying to connect to the result of that call (which is None). So you are trying to connect the signal to None which will of course fail. You need to refer to the method without calling it: just remove the calling brackets.

Putting it together:

  btn.clicked.connect(self.group1.run)

That seems to work.