I would like to show CupertinoPicker, when some button is pressed.
However I have no idea where I should implement CupertinoPicker.

Following code is sample of code which I don't know where I write to call.

```
showCupertinoModalPopup<String>(
  context: context,
  builder:(BuildContext context){
    return _buildBottomPicker(CupertinoPicker(
      onSelectedItemChanged: (value){
        setState((){
          selectedValue = value;
        });
      },
      itemExtent: 32.0,
      children: const[
        Text('Item01'),
        Text('Item02'),
        Text('Item03'),
      ],
    ));
  },
);

```