The actual intention is to only return paren't path, not change the current directory. Have I misunderstood QDir's API? The way it is used here is just to construct current path from mCurrentDir and get it's parent. mCurrentDir is not changed in the function nor is application's current directory (QDir::setCurrent).

So what I need is to get parent's path, and I can then assign it to model's path property to go to parent directory.

I don't think property is as good as function here, see for example faenil's confusion earlier. Not a problem to change, but perhaps it wasn't clear what I wanted the function to do (ie. no side-effects, only return parent path).