Python Qt6 - change font size at runtime

[PythonQTMarlem]

Hello,
I tried this code:

def change_font(self):
        print("Change font")
        fontsize = int(self.cbxfontsize.currentText())
        app.setStyleSheet("""QPushButton{font-size: 18pt;}""")

The good news is my Python program doesn't crash. The bad news is, the code doesn't change the font size at runtime.

Question:
How does it work?

[JonB]

@PythonQTMarlem
I don't know whether it will address your issue, but: the embedded double-quotes you have are not supposed to be there, and might stop it taking effect. It should be app.setStyleSheet("QPushButton{font-size: 18pt;}"). I presume you are also aware that this line does not use the fontsize from your combobox.

[PythonQTMarlem]

Thank you for your reply. Unfortunately that's not the solution. My goal is for the user to be able to select the font size from a combo box, but first I need to figure out how to change the font size in a Python Qt6 application at runtime in general.

[PythonQTMarlem]

The following attempt doesn't work either:

self.btn_programm_beenden = QPushButton("&Ende", self)
self.btn_programm_beenden.setStyleSheet('font-size: 20px')
self.btn_programm_beenden.setGeometry(240, 160, 100, 30)
self.btn_programm_beenden.setAccessibleDescription('Programm beenden')
self.btn_programm_beenden.setToolTip('Programm beenden')
self.btn_programm_beenden.setDefault(True)
self.btn_programm_beenden.clicked.connect(self.programm_beeden)
self.btn_programm_beenden.setFont(QFont('Arial', 18))

No error message appears, but the font size is not changed either.

[PythonQTMarlem]

This works!

    def schrift_aendern(self):
        print("Schrift ändern")
        fontsize = int(self.cbxschriftgroesse.currentText())
        self.btn_programm_beenden.setStyleSheet('font-size: ' + str(fontsize)+'px')

Question:
Is there a smart solution how I can apply this (maybe with a loop) to all QPushButton, QLabel and QLineEdit?

[JonB]

@PythonQTMarlem
I don't understand: you said earlier

self.btn_programm_beenden.setStyleSheet('font-size: 20px')

didn't work, and now you say

self.btn_programm_beenden.setStyleSheet('font-size: ' + str(fontsize)+'px')

does work.

[PythonQTMarlem]

@PythonQTMarlem said in Python Qt6 - change font size at runtime:

self.btn_programm_beenden.setStyleSheet('font-size: 20px')

This:

self.btn_programm_beenden.setStyleSheet('font-size: 20px')

was in the create function. was in the create function.

I tried to change the fontsize for the whole application:

app.setStyleSheet("""QPushButton{font-size: 18pt;}""")

it doesn't work no matter how i write it.
now I had the idea to change the font size for only one QPushbutton:

fontsize = int(self.cbxschriftgroesse.currentText())
self.btn_programm_beenden.setStyleSheet('font-size: ' + str(fontsize)+'px')

this works at runtime!