I think you could do it with the combination of a masked line edit, and a QRegExpValidator that checks for a regex like this: (?:1\d?\d?|2(?:[0-4]\d?|[6789]|5[0-5]?)?|[3-9]\d?|0)(?:\.(?:1\d?\d?|2(?:[0-4]\d?|[6789]|5[0-5]?)?|[3-9]\d?|0)){3}

That said, I haven't tried this myself, so who knows...