Using a checkbox in pyqt

Question

1) I have a checkbox called "ch_check" in my UI created with Qt designer that needs to be tested

2) There is also a button, "bt_button", which triggers a simple function:

self.dlg.bt_button.clicked.connect(self.doCheck)

3) The function:

def doCheck(self):
    if ch_check.isChecked():
        self.dlg.le_text.setText("Hello")
    else:
        self.dlg.le_text.setText("Nope")

However I can't figure out how to reference the box properly. How would I do that? Do I need to connect the checkbox somehow first? All the examples I found so far use checkboxes to fire off functions and whatnot while completely ignoring this basic usage. I found this question but it's not answering how to address the existing checkbox: How to check if a checkbox is checked in pyqt

Answer 1

You can do this utilizing the StateChanged signal. For this example we have a simple .ui and a simple .py file:

The .ui file defines two widgets. A check box (ch_check) and a single QLabel (my_label)

The python file:

from PyQt4 import QtCore
from PyQt4 import QtGui 
import sys
from test_ui import Ui_MainWindow

class CheckDialog(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QWidget.__init__(self)

        # Set up the user interface from Designer.
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        self.ui.ch_check.stateChanged.connect(self.state_changed)

    def state_changed(self, int):
        if self.ui.ch_check.isChecked():
            self.ui.my_label.setText("CHECKED!")
        else:
            self.ui.my_label.setText("UNCHECKED!")


if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    window = CheckDialog()
    window.show()
    sys.exit(app.exec_())

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Explanation:

We set up our signal with this line:

self.ui.ch_check.stateChanged.connect(self.state_changed)

When the state of the checkbox changes, it will call the state_changed function. This is where your logic to check whether the box is checked or unchecked goes.

def state_changed(self, int):
    if self.ui.ch_check.isChecked():
        self.ui.my_label.setText("CHECKED!")
    else:
        self.ui.my_label.setText("UNCHECKED!")

In the function, we determine if the check box has been checked. If so, we change our label to say "CHECKED", if it is unchecked the label changes to "UNCHECKED".

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Example:

When the application is launched the UI looks like this:

Checking the box, changes the label:

Unchecking the box, also changes the label: