Im trying to make an Star Pattern Generator in Flutter. I pass Data from type int in a callback function from the child widget: Textfield Widget to the parent Widget CustomBarWidget and after to the Toplevel parent Widget RootPage.

At the Textfield I got an Error at the Line:

onChanged: widget.onChange,

The Error says: The argument type 'dynamic Function(int)' can't be assigned to the parameter type void Function(String)?

Here is the Full Code:

RootPage:

class RootPage extends StatefulWidget {
  const RootPage({super.key});

  @override
  State<RootPage> createState() => _RootPageState();
}

class _RootPageState extends State<RootPage> {
  int data = 5;

  void getData(int newNumb) {
    setState(() {
      data = newNumb;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: CustomBarWidget(sendData: getData),
      body: StarTriangleWidget(data: data),
    );
  }
}

CustomBarWidget:

class CustomBarWidget extends StatefulWidget implements PreferredSizeWidget {
  const CustomBarWidget({super.key, this.sendData});
  final sendData;

  @override
  Size get preferredSize => const Size.fromHeight(70.0);

  @override
  State<CustomBarWidget> createState() => _CustomBarWidgetState();
}

class _CustomBarWidgetState extends State<CustomBarWidget> {
  int data = 0;

  @override
  Widget build(BuildContext context) {
    return AppBar(
      backgroundColor: Colors.transparent,
      elevation: 0,
      title: Row(
        children: <Widget>[
          TextfielWidget(onChange: (val) {
            widget.sendData(val);
          }),
          ElevatedButton(
            onPressed: () {
              debugPrint("click");
            },
            style: ElevatedButton.styleFrom(
              padding:
                  const EdgeInsets.symmetric(horizontal: 40.0, vertical: 15.0),
              shape: const StadiumBorder(),
            ),
            child: const Text(
              "Enter",
              style: TextStyle(color: Colors.white, fontSize: 18),
            ),
          ),
        ],
      ),
    );
  }
}

textfieldWidget:

class TextfielWidget extends StatefulWidget {
  final Function(int) onChange;

  const TextfielWidget({super.key, required this.onChange});

  @override
  State<TextfielWidget> createState() => _TextfielWidgetState();
}

class _TextfielWidgetState extends State<TextfielWidget> {
  @override
  Widget build(BuildContext context) {
    return Flexible(
        child: TextField(
            onChanged: widget.onChange,
            keyboardType: TextInputType.number,
            decoration: const InputDecoration(
              border: OutlineInputBorder(),
              labelText: 'Enter Number',
            )
          )
        );
  }
}

Where can I change the type of "void Function(String)?"? I can't find the Problem, is the Problem the Textfield itself?

Thank you for help

CodePudding user response：

the onChanged property of TextField accepts a void Function(String)?, but the widget.onChange that you assigned to it returns a Function(int) and it's not void so dart expects something to be returned and handles it like dynamic Function(int), so the solution is to :

change this:

  final Function(int) onChange;

with this:

  final void Function(String)? onChange;

now you say that the value got from the TextField is String, and I understand that you need to get a number from the task you are doing in your app, so whenever you have a String containing a number such as "120" you can convert it to int such as 120 with :

int parsedNumber = int.parse("120"); // 120

your implementation in the onChanged property seems like this :

TextfielWidget(onChange: (val) {
        widget.sendData(val);
      }),

here the val should be String, but you can parse it so it can be int inside the sendData method like this :

 TextfielWidget(onChange: (val) {
            widget.sendData(int.parse(val));
          }),

it will work fine now.

Note: the int.parse(val) will work fine if the val contains only numbers, otherwise, it will throw an Exception if you want that it will return null if there is a problem use instead int.tryParse(val);

Hope this helps.

CodePudding user response：

TextField's onChanged property is type void Function(String) not void Function(int). change all your function type and convert the string to int:

 int data = 5;

  void getData(String newNumb) {
    setState(() {
      data = int.tryParse(newNumb);
    });
  }