TDDropdownMenu _buildDownChunk(BuildContext context) {
  return TDDropdownMenu(
    direction: TDDropdownMenuDirection.down,
    items: [
      TDDropdownItem(
        label: '单列多选',
        multiple: true,
        options: [
          TDDropdownItemOption(label: '选项1', value: '1', selected: true),
          TDDropdownItemOption(label: '选项2', value: '2'),
          TDDropdownItemOption(label: '选项3', value: '3'),
          TDDropdownItemOption(label: '选项4', value: '4'),
          TDDropdownItemOption(label: '选项5', value: '5'),
          TDDropdownItemOption(label: '选项6', value: '6'),
          TDDropdownItemOption(label: '选项7', value: '7'),
          TDDropdownItemOption(label: '选项8', value: '8'),
          TDDropdownItemOption(label: '禁用选项', value: '9', disabled: true),
        ],
        onChange: (value) {
          print('选择：$value');
        },
        onConfirm: (value) {
          print('确定选择：$value');
        },
        onReset: () {
          print('清空选择');
        },
      ),
      TDDropdownItem(
        label: '双列多选',
        multiple: true,
        optionsColumns: 2,
        options: [
          TDDropdownItemOption(label: '选项1', value: '1', selected: true),
          TDDropdownItemOption(label: '选项2', value: '2', selected: true),
          TDDropdownItemOption(label: '选项3', value: '3'),
          TDDropdownItemOption(label: '选项4', value: '4'),
          TDDropdownItemOption(label: '选项5', value: '5'),
          TDDropdownItemOption(label: '选项6', value: '6'),
          TDDropdownItemOption(label: '选项7', value: '7'),
          TDDropdownItemOption(label: '选项8', value: '8'),
          TDDropdownItemOption(label: '禁用选项', value: '9', disabled: true),
          TDDropdownItemOption(label: '禁用选项', value: '10', disabled: true),
        ],
      ),
      TDDropdownItem(
        label: '三列多选',
        multiple: true,
        optionsColumns: 3,
        options: [
          TDDropdownItemOption(label: '选项1', value: '1', selected: true),
          TDDropdownItemOption(label: '选项2', value: '2', selected: true),
          TDDropdownItemOption(label: '选项3', value: '3', selected: true),
          TDDropdownItemOption(label: '选项4', value: '4'),
          TDDropdownItemOption(label: '选项5', value: '5'),
          TDDropdownItemOption(label: '选项6', value: '6'),
          TDDropdownItemOption(label: '选项7', value: '7'),
          TDDropdownItemOption(label: '选项8', value: '8'),
          TDDropdownItemOption(label: '选项9', value: '9'),
          TDDropdownItemOption(label: '禁用选项', value: '10', disabled: true),
          TDDropdownItemOption(label: '禁用选项', value: '11', disabled: true),
          TDDropdownItemOption(label: '禁用选项', value: '12', disabled: true),
        ],
      ),
    ],
  );
}