如何显示，在颤动的下拉列表中选择传递的值

Question

in flutter code initial item how I pass same year which I getting in _year value in the dropdown as selected ========================================================================

         Container(
                          height: 100,
                          width: 48,
                          child: CupertinoPicker(
                            squeeze: 1.3,
                            itemExtent: 30,
                            backgroundColor: Colors.white,
                            children: _getYearList(),
                            scrollController: FixedExtentScrollController(
                              initialItem: DateTime.now().year.compareTo(_year),
                            ),
                            onSelectedItemChanged: (item) {
                              setState(() {
                                 
                                 _year = DateTime.now().year - 30 + item;
                                
                              });
                            },
                          ),
                        ),

this is my _getYearList() method to show year dropdown

List<Widget> _getYearList() {
    List list = new List<Widget>();
    int currentYear = DateTime.now().year - 30;

    print("yearrr : " + currentYear.toString());
    list.contains(_year);
    _year.compareTo(currentYear);
    print("currentYear :" + currentYear.toString());
    //for (int index = currentYear; index <= currentYear + 30; index++) {
    for (int index = currentYear; index <= currentYear + 30; index++) {
      list.add(Container(
        alignment: Alignment.center,
        child: Text(
          '$index',
          //'$index - ${index + 1}',
          style: TextStyle(fontSize: 16),
        ),
      ));
    }

    return list;
  }

Answer 1

If I got the question right... The way to identify the value change in CupertinoPicker/DropdownButton is the callback function of onSelectedItemChanged/onChanged which is used in your code. The callback function has an argument void Function(T value) which is the selected value. You can have a member of T type and keep there changed value in case of onSelectedItemChanged/onChanged via setState(){...}.