问如何使用getx在颤振中添加下拉按钮？

EN

Widget build(BuildContext context) {
  Controller controller = Get.put(Controller());
  return Column(
    children: [
      SingleChildScrollView(
        scrollDirection: Axis.vertical,
        child: SingleChildScrollView(
          scrollDirection: Axis.horizontal,
          child: DataTable(columns: [
            DataColumn(
              label: Text('Order No'),
            ),
            DataColumn(
              label: Text('Quantity'),
            ),
            DataColumn(
              label: Text('Retail Price'),
            ),
            DataColumn(
              label: Text('Payment Status'),
            ),
            DataColumn(
              label: Text('Date'),
            ),
            DataColumn(
              label: Text('Assign Rider'),
            ),
          ], rows: [
            DataRow(
                cells: [
              DataCell(Text('637c8e3a')),
              DataCell(Text('1')),
              DataCell(Text('1.00')),
              DataCell(Text('UnPaid')),
              DataCell(
                Text('2022-11-22 08:54:18'),
              ),
              DataCell(
                Obx( () => DropdownButton(
                  hint: Text(
                    'Book Type',
                  ),
                  onChanged: (newValue) {
                    controller.setSelected(newValue);
                  },
                  value: controller.selected.value,
                  items: controller.listType.map((selectedType) {
                    return DropdownMenuItem(
                      child: new Text(
                        selectedType,
                      ),
                      value: selectedType,
                    );
                  }).toList(),
                )
                ),
              ),
            ])
          ]),
        ),
      )
    ],
  );
}

final selected = "".obs;

void setSelected(String value){
  selected.value = value;
}

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lib/widget/data_table.dart:52:46: Error: The argument type 'Object?' can't be assigned to the parameter type 'String'.
 - 'Object' is from 'dart:core'.
                      controller.setSelected(newValue);
                                             ^
lib/widget/data_table.dart:55:39: Error: The getter 'listType' isn't defined for the class 'Controller'.
 - 'Controller' is from 'package:vendor_app/controller/dropdown_controller.dart' ('lib/controller/dropdown_controller.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'listType'.
                    items: controller.listType.map((selectedType) {
                                      ^^^^^^^^