I have a dropdown list populated with users, I want to get the user id and pass to a function whenever a user is selected from the list

An unhandled exception is occurring instead

the exception

E/flutter (28482): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: Null check operator used on a null value

The below snippet is where how I am fetching the users

User? sid;
  List<User> users = [];

  //fetch users
  Future<List<User>>? getUsers() async {
    var result = await client.get(usersUrl);
    return userFromJson(result.body);
  }

  Future<void> fetchandShow() async {
    final users = await getUsers();
    setState(() {
      this.users = users ?? [];
    });
  }

  @override
  void initState() {
    super.initState();
    fetchandShow();
  }

below is the dropdownbutton where I am displaying the users

DropdownButtonFormField<User>(
                    hint: Text('Select user'),
                    decoration: InputDecoration(
                      border: InputBorder.none,
                    ),
                    value: sid,
                    items: users
                        .map((item) => DropdownMenuItem(
                              value: item,
                              child: Text(
                                item.username,
                                style: TextStyle(fontSize: 20.0),
                              ),
                            ))
                        .toList(),
                    onChanged: (item) => setState(() {
                      sid!.id = item as String?;
                      print(sid!.id);
                    }),
                  ),

below is where i want to pass the user id

ElevatedButton(
                onPressed: () async {
                  await createNote(
                      _bodyController.text, int.parse(sid!.id.toString()));
                  Navigator.pop(context);
                },
                child: Text('submit'),
              )

CodePudding user response：

Your item is of User type, Handle onChanged as below:

       onChanged: (item) => setState(() {
                  sid = item;
                 
                }),

CodePudding user response：

Here "timeZoneType" is the List of data and once the user select any option from the dropdown, we will get the index ("accountIndex") of the item. Once we get the index of the item, we can just get that index item details by

"timeZoneType[index]"

var detailData = timeZoneType[index]

Column(
    children: [
    Container(
    width: MediaQuery.of(context).size.width,
    height: 45,
    child: DropdownButtonHideUnderline(
    child: Padding(
    padding: const EdgeInsets.only(left: 20.0, right: 1),
    child: DropdownButton(
    hint: Text("Timezone", style: Constants.editTextStyleLight),
    value: _currentSelectedValue.value,
    items: timeZoneType
        .map((String value) {
    return DropdownMenuItem<String>(
    value: value,
    child: Text(
    value,
    style: Constants.editTextStyle,
    ),
    );
    }).toList(),
    onChanged: (value) {
    setState(() {
    print(value);
    accountIndex = timeZoneType.indexOf(value.toString());
    print(accountIndex);
    
    });
    }),
    ),
    ),
    ),
    ],
    )