DropdownButton in flutter is giving error. How to fix?-CodePudding

I have to use a DropdownButton() in my flutter app and I was getting some exceptions. Am I doing anything wrong and how do I go about fixing this?

...

class _CreateNewsArticleState extends State<CreateNewsArticle> {
  String dropdownvalue = 'Publish';
  var items = [
    'Publish at 22:00',
    'Publish in 9 hrs',
    'Publish in 5 hrs',
    'Publish in 3 hrs',
    'Publish in 1 hr',
    'Publish now'
  ];
  @override
  Widget build(BuildContext context) {

...

This is the flutter DropdownButton() widget

DropdownButton(
                              value: dropdownvalue,
                              icon: Icon(Icons.arrow_forward_ios),
                              items: items.map((String items) {
                                return DropdownMenuItem(
                                    value: items, child: Text(items));
                              }).toList(),
                              onChanged: (value) {
                                setState(() {
                                  dropdownvalue = "value";
                                });
                              },
                            )

error

Object? value
Type: Object?

A value of type 'Object?' can't be assigned to a variable of type 'String'.
Try changing the type of the variable, or casting the right-hand type to 'String'.dartinvalid_assignment

CodePudding user response：

In your setState you are not setting the var value but a String "value".

 setState(() {
      dropdownvalue = value;
    });

Also, keep in mind that your dropdownvalue must be one of your values list or this will cause an Exception (There should be exactly one item with [DropdownButton]'s value)

As mentioned by Maikzen declare your list as a List<String> and the DropdrownMenuItems as DropdownMenuItem<String>.

CodePudding user response：

Declare your list as List:

List<String> items = [
    'Publish at 22:00',
    'Publish in 9 hrs',
    'Publish in 5 hrs',
    'Publish in 3 hrs',
    'Publish in 1 hr',
    'Publish now'
  ];

Change your dropdownbutton like that:

DropdownButton<String>(
                              value: dropdownvalue,
                              icon: Icon(Icons.arrow_forward_ios),
                              items: items.map((String items) {
                                return DropdownMenuItem<String>(
                                    value: items, child: Text(items));
                              }).toList(),
                              onChanged: (value) {
                                setState(() {
                                  dropdownvalue = "value";
                                });
                              },
                            )

You need to declare your type of data in your dropdown.