Android Studio – How can i show a column or container inside DropDownButton? flutter

try this and change this code as you want

class MyApp2 extends StatefulWidget {
  const MyApp2({Key? key}) : super(key: key);

  @override
  State<MyApp2> createState() => _MyApp2State();
}

class _MyApp2State extends State<MyApp2> {
  List<CustomDropDownItem> items =
      List.generate(10, (index) => CustomDropDownItem("item $index", "item $index", "item $index"));
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
            child: SingleChildScrollView(
      child: Column(children: [
        const Text("Custom DropDown"),
        CustomDropDown(
          items: items,
          height: 300,
          onChanged: (selectedItem, selectedIndex) {
            print(selectedItem.value);
          },
        ),
     
        ...List.generate(
            20,
            (index) => Card(
                  child: ListTile(
                    title: Text("Custom Widget $index"),
                  ),
                ))
      ]),
    )));
  }
}

class CustomDropDownItem {
  String text;
  String value;
  // change it as you want, string or image path or QR or widget
  String info;
  CustomDropDownItem(this.text, this.value, this.info);
}

class CustomDropDown extends StatefulWidget {
  final List<CustomDropDownItem> items;
  final Function(CustomDropDownItem selectedItem, int selectedIndex) onChanged;
  final double height;
  const CustomDropDown({Key? key, required this.items, required this.onChanged, this.height = 300}) : super(key: key);
  @override
  _CustomDropDownState createState() => _CustomDropDownState();
}

class _CustomDropDownState extends State<CustomDropDown> {
  final _controller = TextEditingController();
  bool _showItems = false;
  CustomDropDownItem? _selectedItems;
  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Padding(
          padding: const EdgeInsets.all(8.0),
          child: TextField(
            controller: _controller,
            readOnly: true,
            onTap: () {
              setState(() {
                _showItems = !_showItems;
              });
            },
            decoration: InputDecoration(
                border: const OutlineInputBorder(),
                suffixIcon: _showItems ? const Icon(Icons.arrow_upward) : const Icon(Icons.arrow_downward)),
          ),
        ),
        Padding(
          padding: const EdgeInsets.all(8.0),
          child: Material(
            elevation: 20,
            child: AnimatedContainer(
              duration: const Duration(milliseconds: 200),
              decoration: BoxDecoration(borderRadius: BorderRadius.circular(25)),
              height: _showItems ? widget.height : 0,
              child: Opacity(
                opacity: _showItems ? 1 : 0,
                child: Row(
                  children: [
                    Expanded(
                        child: SingleChildScrollView(
                      child: Column(
                        children: List.generate(
                            widget.items.length,
                            (index) => Card(
                                  child: ListTile(
                                    trailing: GestureDetector(
                                      onTap: () {
                                        setState(() {
                                          _selectedItems = widget.items[index];
                                        });
                                      },
                                      child: const Icon(Icons.details),
                                    ),
                                    title: Text(widget.items[index].text),
                                    onTap: () {
                                      _controller.text = widget.items[index].value;
                                      widget.onChanged(widget.items[index], index);
                                      setState(() {
                                        _showItems = false;
                                      });
                                    },
                                  ),
                                )),
                      ),
                    )),
                    Container(
                      color: Colors.grey,
                      width: 5,
                      height: double.infinity,
                    ),
                    Expanded(
                        child: Container(
                      width: double.infinity,
                      height: double.infinity,
                      alignment: Alignment.center,
                      // change it as you want
                      child: Text(_selectedItems?.info ?? widget.items.first.info),
                    )),
                  ],
                ),
              ),
            ),
          ),
        ),
      ],
    );
  }
}