CODEWITHSUNDEEP
flutterdartnullable
Ahmed Maged
Ahmed Maged

Reputation: 3

The argument type 'String?' can't be assigned to the parameter type 'String' in flutter

'The argument type 'String?' can't be assigned to the parameter type 'String' because 'String?' is nullable and 'String' isn't' pleas can any one help me with this error. i faced this error will trying to make extracting widget

import 'package:flutter/material.dart';
import 'quote.dart';

void main() => runApp(const MaterialApp(
  home: QuoteList() ,
));

class QuoteList extends StatefulWidget {
  const QuoteList({Key? key}) : super(key: key);

  @override
  State<QuoteList> createState() => _QuoteListState();
}

class _QuoteListState extends State<QuoteList> {

  List<Quote> quotes = [
      Quote(text: 'This is the quote number 1',author: 'Ahmed Maged'),
      Quote(text: 'This is the quote number 2',author: 'Kareem Khaled'),
      Quote(text: 'This is the quote number 3',author: 'Ahmed Shoman'),
  ];

  Widget quoteTemplate(quote){
    return QuoteCard(quote: quote);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.grey[200],
      appBar: AppBar(

        title: const Text(
          'List of Data',
          style: TextStyle(
            color: Colors.white,
            letterSpacing: 2.0,
            fontWeight: FontWeight.bold,
            fontSize: 20.0,
            fontFamily:'FiraSans',
          ),
        ),
        backgroundColor: Colors.black38,
        centerTitle: true,
      ),
      body: Column(
        children: quotes.map((quote) => quoteTemplate(quote)).toList(),
      ),
    );
  }
}

class QuoteCard extends StatelessWidget {
  final Quote? quote;
  const QuoteCard({super.key, this.quote});

  @override
  Widget build(BuildContext context) {
    return Card(
        margin: const EdgeInsets.fromLTRB(16.0, 16.0, 16.0, 0),
        child: Padding(
          padding: const EdgeInsets.all(12.0),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: [
              Text(
                quote.text, // error part
                style: const TextStyle(
                  letterSpacing: 2.0,
                  fontSize: 18.0,
                  fontWeight: FontWeight.bold,
                ),
              ),
              const SizedBox(height: 6.0,),
              Row(
                mainAxisAlignment: MainAxisAlignment.end,
                children: [
                  Text(
                    quote.author, // error part
                    style: const TextStyle(
                      letterSpacing: 2.0,
                      fontSize: 14.0,
                      fontFamily: 'FiraSans',
                    ),
                  ),
                ],
              ),
            ],
          ),
        ),
      );
  }
}

this is the qoute file quote.dart file:

class Quote {
  String? text;
  String? author;

  Quote({required this.text, required this.author});

}

it just alisson from the net ninja lesson number #20

Upvotes: 0

Views: 426

Answers (1)

Munsif Ali
Munsif Ali

Reputation: 5792

This error in Flutter occurs when you are passing a nullable string (String?) to a function or method that expects a non-nullable string (String). To resolve the error, you can either make sure the string being passed is not null or update the function or method to accept a nullable string. You can also use the ?? operator to provide a default value for the string in case it is null. try this:

 Text(
                quote.author??"", // error part
                style: const TextStyle(
                  letterSpacing: 2.0,
                  fontSize: 14.0,
                  fontFamily: 'FiraSans',
                ),

and this

 Text(
            quote.text, // error part
            style: const TextStyle(
              letterSpacing: 2.0,
              fontSize: 18.0,
              fontWeight: FontWeight.bold,
            ),
          ),

the solution for your commented error is

class QuoteCard extends StatelessWidget {
final Quote quote;
const QuoteCard({super.key,required this.quote});

@override
Widget build(BuildContext context) {
return Card(
    margin: const EdgeInsets.fromLTRB(16.0, 16.0, 16.0, 0),
    child: Padding(
      padding: const EdgeInsets.all(12.0),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: [
          Text(
            quote.text, // error part
            style: const TextStyle(
              letterSpacing: 2.0,
              fontSize: 18.0,
              fontWeight: FontWeight.bold,
            ),
          ),
          const SizedBox(height: 6.0,),
          Row(
            mainAxisAlignment: MainAxisAlignment.end,
            children: [
              Text(
                quote.author, // error part
                style: const TextStyle(
                  letterSpacing: 2.0,
                  fontSize: 14.0,
                  fontFamily: 'FiraSans',
                ),
              ),
            ],
          ),
        ],
      ),
    ),
  );
 }
}

Upvotes: 1

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