小编Not*_*nix的帖子

我不断收到以下错误：lib/main.dart:45:37: Error: A value of type 'Object?' 不能分配给“字符串”类型的变量。

• “对象”来自“dart:core”。_startMeasure = 值；

这完全有道理，但我尝试将值更改为字符串，但这并不能解决问题。我试过 "$value" 和 _startMeasure = value as String。但是，这些都不起作用。

代码：

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  MyAppState createState() => MyAppState();
}//class

class MyAppState extends State<MyApp> {

  double _numberFrom = 0;
  String _startMeasure = "";
  final List<String> _measures = [
    'meters',
    'kilometers',
    'grams',
    'kilograms',
    'feet',
    'miles',
    'pounds (lbs)',
    'ounces',
  ];

  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(

        appBar: AppBar(
          title: Center(child: Text("Convert Units")),
          backgroundColor: Colors.deepOrange[300], …