如何从另一个列表形成一个列表？

Question

我有一个要在其中选择元素的列表，但是当我选择某个元素时，我希望将其添加到此列表顶部的列表中。如何实施？我认为值得创建一个空数组来添加所选元素，但到目前为止我还没有成功

我的代码是这样的：

  /// add selected items from list
  List multipleSelected = [];
 
/// another list to form the new list above previous one
  List chosenListsAbove = [];

Widget chosendataBase() {
  return FutureBuilder<List>(
    future: BasesService().GetBases(),
    builder: (context, snapshot) {
      List? baseNames = snapshot.data;
      print(baseNames);
      return ListView.builder(
        shrinkWrap: true,
        itemCount: baseNames?.length ?? 0,
        itemBuilder: (context, i) {
          void _onCategorySelected(bool selected, id) {
            if (selected == true) {
              setState(() {
                multipleSelected.add(id);
              });
            } else {
              setState(
                () {
                  multipleSelected.remove(id);
                },
              );
            }
          }

          return ListTile(
              title: Padding(
                padding: const EdgeInsets.only(left: 1.0),
                child: Text(
                  baseNames?[i]['name'] ?? 'not loading',
                  style: TextStyle(
                      fontFamily: 'fonts/Montserrat',
                      fontSize: 24,
                      fontWeight: FontWeight.w900,
                      color: Colors.white),
                ),
              ),
              leading: Checkbox(
                activeColor: Colors.green,
                checkColor: Colors.green,
                side: BorderSide(width: 2, color: Colors.white),
                value: multipleSelected.contains(baseNames?[i]['id']),
                onChanged: (bool? selected) {
                  _onCategorySelected(selected!, baseNames?[i]['id']);
                },
              )
              //you can use checkboxlistTile too
              );
        },
      );
    },
  );
}

Answer 1

像这样你可以做到

    void main() {
  List arr = [1,2,3];
  List arr2 = [];

  arr2.addAll(arr);
  print(arr2);

}

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