How to detect orientation change in layout in Flutter?

Question

How to find out Orientation is portrait or landscape in Flutter

if(portrait){
  return ListView.builder()
}else{
  return GridView.count()
}

Answer 1

For completeness sake, I would like to add another way to detect orientation in Flutter. Two ways to detect have been mentioned in the answers already. They are

1. Media Query
2. Orientation Builder

There is a third way which I came across when learning Flutter from Responsive Design video (skip to minute 2:34) by Google Engineers. It's called Layout Builder. Here is short snippet:

return Padding(
    padding: _padding,
    child: LayoutBuilder(
        builder: (BuildContext context, BoxConstraints constraints) {
            if(constraints.maxHeight > constraints.maxWidth) {
                return _getPortraitLayout();
            }
            else {
                return _getLandscapeLayout();
            }
        },
    ),
);