QFileDialog::getFileName how to set default extension?

[Talei]

Or something like this:

QFileDialog::getOpenFileName(this, tr("Open TXT File"),
                                                    "",
                                                    tr("Plain text file (*.txt)"));

QFileDialog::getOpenFileName(this, tr("Open TXT File"),
                                                    "",
                                                    tr("Plain text file (*.txt)"));

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