如何从有状态小部件中获取参数

Question

How do I get access to the _selectedCurrency parameter which inside the following stateful class from another stateful class?

import 'dart:io' show Platform;

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

import 'coin_data.dart';

class OsPicker extends StatefulWidget {
  @override
  _OsPickerState createState() => _OsPickerState();
}

class _OsPickerState extends State<OsPicker> {
  String _selectedCurrency = currenciesList[0];

  DropdownButton<String> androidDropDown() {
    List<DropdownMenuItem<String>> dropdownItems = [];

    for (String currency in currenciesList) {
      var newItem = DropdownMenuItem(
        child: Text(currency),
        value: currency,
      );

      dropdownItems.add(newItem);
    }

    return DropdownButton<String>(
      value: _selectedCurrency,
      items: dropdownItems,
      onChanged: (value) {
        setState(() {
          _selectedCurrency = value;
        });
      },
    );
  }

  CupertinoPicker iOSPicker() {
    List<Text> pickerItems = [];

    for (String currency in currenciesList) {
      var newItem = Text(currency);
      pickerItems.add(newItem);
    }

    return CupertinoPicker(
        backgroundColor: Colors.lightBlue,
        itemExtent: 32.0,
        onSelectedItemChanged: (selectedIndex) {
          setState(() {
            _selectedCurrency = currenciesList[selectedIndex];
            print(_selectedCurrency);
          });
        },
        children: pickerItems);
  }

  @override
  Widget build(BuildContext context) {
    return Platform.isIOS ? iOSPicker() : androidDropDown();
  }
}

The following is from the coin_dart file:

const List currenciesList = [ 'AUD', 'BRL', 'CAD', 'CNY', 'EUR', 'GBP', 'HKD', 'IDR', 'ILS', 'INR', 'JPY', 'MXN', 'NOK', 'NZD', 'PLN', 'RON', 'RUB', 'SEK', 'SGD', 'USD', 'ZAR' ];

const List cryptoList = [ 'BTC', 'ETH', 'LTC', ];

Answer 1

You can't, the data in Flutter are descending only. A workaround would be to create a global file to store your variables or to use a design pattern like BLoC which allow you to access data from anywhere in your application.

Example of Global

// global.dart
String selectedCurrency;

// Then you can do as follow to access it
import './lib/global.dart' as Globals;

Globals.selectedCurrency = currenciesList[0];