Code completion doesn't work in case MyStringList.at(1)

QStringList MyStringList;
MyStringList << "Hello" << "World" << "!";
MyStringList.at(1).

and if I start typing dot here, qtcreator doesn't offer code completion for me I don't understand why ?
I would like to type a method related to QString. I have tried with [1] as well, but that didn't work either, what can be the problem ?

I don't know whether the template format causes problem for it, but I think the type is here rather trivial.