Solution:
Controller.prototype.IntroductionPageCallback = function()
{
// Installer is "updater" when it is run with "--updater"
// or Controller does "installer.setUpdater()"
if (installer.isUpdater()) {
var widget = gui.currentPageWidget(); // Same as gui.pageById(QInstaller.Introduction);
widget.findChild("UpdaterRadioButton").checked = true;
// Disable paint events on these widgets, through the QWidget::updatesEnabled property.
// I tried with the "visible" property, but it is not enough, because for some reason
// that property gets reset under some conditions. For example, if "Next" button is pressed
// and no updates are available.
widget.findChild("PackageManagerRadioButton").updatesEnabled = false;
widget.findChild("UninstallerRadioButton").updatesEnabled = false;
}
}
