如何在颤动中显示选定的下拉值索引号？

我的下拉菜单工作正常。我可以从下拉列表中选择项目，并在我的应用程序中显示所选项目。现在，我不想显示从下拉列表中选择的项目，而是显示该特定项目的索引号。

我的下拉项目列表

    List<String> qualities = [
    "Creativity",
    "Commitment",
    "Planning",
    "Optimism",
    "Innovative"
  ];

空列表。在这里我存储选定的项目，然后使用 for 循环显示

 List<String> selectedItem_ArrayList = []; //Storing DropDown selected data

我的下拉菜单

DropdownButton<String>(
                          underline: Container(),
                          icon: Icon(Icons.keyboard_arrow_down),
                          iconSize: 24,
                          isExpanded: true,
                          onChanged: (value) {
                            if (!selectedItem_ArrayList.contains(value)) {//=============================================>>>Items Disable after selection
                              setState(() {
                                selectedQualities = value!;
                                selectedItem_ArrayList.add(selectedQualities);
                              });
                            }//==============================================>>>Adding item into list
                          },
                          value: selectedQualities,
                          items: qualities.map((dropdownValue) => DropdownMenuItem(
                                    child: Text(
                                      dropdownValue,
                                      maxLines: 2,
                                      style: TextStyle(
                                        color: selectedItem_ArrayList.contains(dropdownValue)? Colors.grey: null,
                                      ),
                                    ),
                                    value: dropdownValue,
                                  ))
                              .toList(),
                        ),

从下拉列表中显示所选项目

 Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  for (var i = 0; i < selectedItem_ArrayList.length; i++)
                    ListTile(
                      title: Text(selectedItem_ArrayList[i]), //### here I want to show index number of that particular selected item.
                      trailing: GestureDetector(//#################### remove specific index item
                        onTap: () {
                          setState(() {
                            selectedItem_ArrayList.remove(selectedItem_ArrayList[i]);
                          });
                        },
                        child: Icon(
                          Icons.delete_rounded,
                          color: Colors.red,
                        ),
                      ),
                    ),
                ],
              )

为每个项目选择使用indexOf其唯一的显示索引号0

title: Text(selectedItem_ArrayList[i].indexOf(selectedItem_ArrayList[i]).toString()),