Flutter - 2 required argument(s) expected, but 0 found

Question

I'm creating a double listView app, its going well so far but I've hit a snag that I can't seem to fix.

I'm getting the error[dart] 2 required argument(s) expected, but 0 found.

In my eyes this should be an easy fix, I thought I just needed to change...

body: _cryptoWidget(),

to...

body: _cryptoWidget(currency, color),

This hasn't worked, and I still get the error stated above.

This is the code I'm using to stimulate the error;

import 'package:flutter/material.dart';
import 'background.dart';
import 'package:flutter/foundation.dart';
import 'package:cryptick_nice_ui/data/crypto_data.dart';
import 'package:cryptick_nice_ui/modules/crypto_presenter.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => new _HomePageState();
}

class _HomePageState extends State<HomePage> implements CryptoListViewContract {
  CryptoListPresenter _presenter;
  List<Crypto> _currencies;
  bool _isLoading;
  final List<MaterialColor> _colors = [Colors.blue, Colors.indigo, Colors.red];

    List<String> items = [
    "Item 1",
    "Item 2",
    "Item 3",
    "Item 4",
    "Item 5",
    "Item 6",
    "Item 7",
    "Item 8"
  ];

  _HomePageState() {
    _presenter = new CryptoListPresenter(this);
  }

  @override
  void initState() {
    super.initState();
    _isLoading = true;
    _presenter.loadCurrencies();
  }


  @override
  Widget build(BuildContext context) {

  return new Container(
      decoration: new BoxDecoration(
      color: const Color(0xFF273A48),
    ),
    child: new Stack(
      children: <Widget>[
        new Scaffold(
        appBar: new AppBar(
        title: new Text("cryp"),
        elevation: 0.0,
        backgroundColor: Colors.transparent,
      ),
      backgroundColor: Colors.transparent,
          body: _cryptoWidget(),
          )
        ],
      ),
    );
  }

  Widget _cryptoWidget(Crypto currency, MaterialColor color) {
    final _width = MediaQuery.of(context).size.width;
    final _height = MediaQuery.of(context).size.height;
    final headerList = new ListView.builder(
      itemBuilder: (context, index) {
        EdgeInsets padding = index == 0?const EdgeInsets.only(
            left: 20.0, right: 10.0, top: 4.0, bottom: 30.0):const EdgeInsets.only(
            left: 10.0, right: 10.0, top: 4.0, bottom: 30.0);
            _getHtmlUI();
        return new Padding(
          padding: padding,
        );
      },
      scrollDirection: Axis.horizontal,
      itemCount: items.length,
    );
    new Scaffold(
      appBar: new AppBar(
        title: new Text('hello'),
        elevation: 0.0,
        backgroundColor: Colors.transparent,
      ),
      backgroundColor: Colors.transparent,
      body: new Container(
        child: new Stack(
          children: <Widget>[
            new Padding(
              padding: new EdgeInsets.only(top: 10.0),
              child: new Column(
                crossAxisAlignment: CrossAxisAlignment.center,
                mainAxisSize: MainAxisSize.max,
                mainAxisAlignment: MainAxisAlignment.start,
                children: <Widget>[
                  new Align(
                    alignment: Alignment.centerLeft,
                    child: new Padding(
                        padding: new EdgeInsets.only(left: 8.0),
                        child: new Text(
                          'Your Feed',
                          style: new TextStyle(color: Colors.white70),
                        )),
                  ),
                  new Container(
                      height: 300.0, width: _width, child: headerList),
                  new Expanded(child:
                  ListView.builder(
                    itemBuilder: 
                    (context, index) {
                    _getCryptoUI(currency, color);
                  }
                  )
                )
                ],
              ),
            ),
          ],
        ),
      ),
    );

      return new Container(
      decoration: new BoxDecoration(
        color: const Color(0xFF273A48),
      ),
      child: new Stack(
        children: <Widget>[
          new CustomPaint(
            size: new Size(_width, _height),
            painter: new Background(),
          ),
        ],
      ),
    );


  }

  Container _getHtmlUI() {
    return new Container(
              decoration: new BoxDecoration(
                borderRadius: new BorderRadius.circular(10.0),
                color: Colors.lightGreen,
                boxShadow: [
                  new BoxShadow(
                      color: Colors.black.withAlpha(70),
                      offset: const Offset(3.0, 10.0),
                      blurRadius: 15.0)
                ],
                image: new DecorationImage(
                  image: new ExactAssetImage(
                      'assets/img_0.jpg'),
                  fit: BoxFit.fitHeight,
                ),
              ),
//                                    height: 200.0,
              width: 200.0,
              child: new Stack(
                children: <Widget>[
                  new Align(
                    alignment: Alignment.bottomCenter,
                    child: new Container(
                        decoration: new BoxDecoration(
                            color: const Color(0xFF273A48),
                            borderRadius: new BorderRadius.only(
                                bottomLeft: new Radius.circular(10.0),
                                bottomRight: new Radius.circular(10.0))),
                        height: 30.0,
                        child: new Row(
                          mainAxisAlignment: MainAxisAlignment.center,
                          children: <Widget>[
                            new Text(
                              'hello',
                              style: new TextStyle(color: Colors.white),
                            )
                          ],
                        )),
                  )
                ],
              ),
            );
  }

  ListTile _getCryptoUI(Crypto currency, MaterialColor color) {
    return new ListTile(
                      title: new Column(
                        children: <Widget>[
                          new Row(
                            crossAxisAlignment: CrossAxisAlignment.start,
                            children: <Widget>[
                              new Container(
                                height: 72.0,
                                width: 72.0,
                                decoration: new BoxDecoration(
                                    color: Colors.lightGreen,
                                    boxShadow: [
                                      new BoxShadow(
                                          color:
                                          Colors.black.withAlpha(70),
                                          offset: const Offset(2.0, 2.0),
                                          blurRadius: 2.0)
                                    ],
                                    borderRadius: new BorderRadius.all(
                                        new Radius.circular(12.0)),
                                    image: new DecorationImage(
                                      image: new ExactAssetImage(
                                        "cryptoiconsBlack/"+currency.symbol.toLowerCase()+"@2x.png",
                                      ),
                                      fit: BoxFit.cover,
                                    )),
                              ),
                              new SizedBox(
                                width: 8.0,
                              ),
                              new Expanded(
                                  child: new Column(
                                    mainAxisAlignment:
                                    MainAxisAlignment.start,
                                    crossAxisAlignment:
                                    CrossAxisAlignment.start,
                                    children: <Widget>[
                                      new Text(
                                        currency.name,
                                        style: new TextStyle(
                                            fontSize: 14.0,
                                            color: Colors.black87,
                                            fontWeight: FontWeight.bold),
                                      ),
                                      _getSubtitleText(currency.price_usd, currency.percent_change_1h),
                                    ],
                                  )),
                              new Icon(
                                Icons.shopping_cart,
                                color: const Color(0xFF273A48),
                              )
                            ],
                          ),
                          new Divider(),
                        ],
                      ),
                    );
  }


  Widget _getSubtitleText(String priceUSD, String percentageChange) {
    TextSpan priceTextWidget = new TextSpan(
        text: "\$$priceUSD\n", style: new TextStyle(color: Colors.black));
    String percentageChangeText = "1 hour: $percentageChange%";
    TextSpan percentageChangeTextWidget;

    if (double.parse(percentageChange) > 0) {
      percentageChangeTextWidget = new TextSpan(
          text: percentageChangeText,
          style: new TextStyle(color: Colors.green));
    } else {
      percentageChangeTextWidget = new TextSpan(
          text: percentageChangeText, style: new TextStyle(color: Colors.red));
    }

    return new RichText(
        text: new TextSpan(
            children: [priceTextWidget, percentageChangeTextWidget]));
  }

  @override
  void onLoadCryptoComplete(List<Crypto> items) {
    // TODO: implement onLoadCryptoComplete

    setState(() {
      _currencies = items;
      _isLoading = false;
    });
  }

  @override
  void onLoadCryptoError() {
    // TODO: implement onLoadCryptoError
  }

}

For more information on other files I use in this app, for instance crypto_data.dart, please see this GitHub repo that I'm using to model certain sections of my code.

Answer 1

The reason why you're getting the error [dart] 2 required argument(s) expected, but 0 found. is because no arguments were passed. The another example you've provided: _cryptoWidget(currency, color) - you're trying to pass a List, which doesn't match the required arguments.

As mentioned in the comments, what you can do here is to define the index for the List to fetch the required values: _cryptoWidget(_currencies[index], _colors[index])