How to create a simple drop down list in flutter with the ability to search for elements in the dropdown list

Try With this package dropdown_textfield:

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

  @override
  State<DropDownButton> createState() => _DropDownButtonState();
}

class _DropDownButtonState extends State<DropDownButton> {
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
  FocusNode searchFocusNode = FocusNode();
  FocusNode textFieldFocusNode = FocusNode();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SingleChildScrollView(
        child: Form(
          key: _formKey,
          child: Center(
            child: Padding(
              padding: const EdgeInsets.all(20),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.center,
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  const SizedBox(
                    height: 70,
                  ),
                  const Text(
                    "Dropdown with search Textfield",
                    style: TextStyle(fontWeight: FontWeight.bold),
                  ),
                  const SizedBox(
                    height: 20,
                  ),
                  DropDownTextField(
                    clearOption: false,
                    textFieldFocusNode: textFieldFocusNode,
                    searchFocusNode: searchFocusNode,
                    searchAutofocus: true,
                    dropDownItemCount: 8,
                    searchShowCursor: false,
                    enableSearch: true,
                    searchKeyboardType: TextInputType.number,
                    dropDownList: const [
                      DropDownValueModel(name: 'Flutter', value: "flutter"),
                      DropDownValueModel(name: 'Java', value: "java",),
                      DropDownValueModel(name: 'HTML', value: "html"),
                      DropDownValueModel(name: 'CSS', value: "css",),
                      DropDownValueModel(name: 'PHP', value: "php"),
                    ],
                    onChanged: (val) {},
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }
}

Output: