根据抛出的错误，问题似乎来自您尝试解码的字符串。json响应中的数据是否正确解析为字符串？您可能需要考虑验证json响应中的“compressedData”是否有效，是否可以使用gzip解码。
如果zipText上的值确实访问了dataList中的数据-这是一个List〈Map〈String，String〉〉，请确保您能够通过var zipText = '${_dataList[index]['Data']}';访问“compressedData
除此之外，还需要将GZipDecoder().decodeBytes(Uint8List)中的值解码为String。

decode(String zipText) {
  // if the sample data is a List<Map<String, String>>
  // you need to use the key to access
  // the compressed data from the List item
  // zipText = '${_dataList[0]['Data']}';
  Uint8List compressed = base64.decode(zipText);
  var gzipBytes = new GZipDecoder().decodeBytes(compressed);

  // Decode List<int> to String
  var stringDecoded = utf8.decode(gzipBytes);
  debugPrint('decoded: $stringDecoded');

  setState(() {
    _textEditingControllerEncode.text = stringDecoded;
  });
}

下面是一个简单的沙箱，您可以使用它。本示例中的decode(String)方法使用您提供的代码片段。

import 'dart:convert';
import 'dart:typed_data';

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final _formEncodeKey = GlobalKey<FormState>();
  final _formDecodeKey = GlobalKey<FormState>();
  final _textEditingControllerEncode = TextEditingController();
  final _textEditingControllerDecode = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          children: [
            Expanded(
              child: Form(
                key: _formEncodeKey,
                child: Column(
                  children: <Widget>[
                    TextFormField(
                      controller: _textEditingControllerEncode,
                      decoration: InputDecoration(
                          hintText: 'Enter some text to Encode'),
                      validator: (value) {
                        if (value == null || value.isEmpty) {
                          return 'Please enter some text to Encode';
                        }
                        return null;
                      },
                    ),
                    ElevatedButton(
                      onPressed: () {
                        if (_formEncodeKey.currentState!.validate()) {
                          encode(_textEditingControllerEncode.value.text);
                        }
                      },
                      child: Text('Encode'),
                    ),
                  ],
                ),
              ),
            ),
            Expanded(
              child: Form(
                key: _formDecodeKey,
                child: Column(
                  children: <Widget>[
                    TextFormField(
                      controller: _textEditingControllerDecode,
                      decoration: InputDecoration(
                          hintText: 'Enter some text to Decode'),
                      validator: (value) {
                        if (value == null || value.isEmpty) {
                          return 'Please enter some text to Decode';
                        }
                        return null;
                      },
                    ),
                    ElevatedButton(
                      onPressed: () {
                        if (_formDecodeKey.currentState!.validate()) {
                          decode(_textEditingControllerDecode.value.text);
                        }
                      },
                      child: Text('Decode'),
                    ),
                  ],
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }

  var _dataList = [
    {"Data": "H4sIABqe5GAA//NIzcnJVyjPL8pJUQQAlRmFGwwAAAA="}, // Hello world!
    {"Data": "H4sIABuk5GAA/3PLKS0pSS1SKMpPzi5WBADZNee+DgAAAA=="} // Flutter rocks!
  ];

  encode(String zipText) {
    var stringBytes = utf8.encode(zipText);
    var gzipBytes = GZipEncoder().encode(stringBytes);
    var stringEncoded = base64.encode(gzipBytes!);
    debugPrint('encoded: $stringEncoded');

    setState(() {
      _textEditingControllerEncode.clear();
      _textEditingControllerDecode.text = stringEncoded;
    });
  }

  decode(String zipText) {
    // if the sample data is a List<Map<String, String>>
    // you need to use the key to access
    // the compressed data from the List item
    // zipText = '${_dataList[0]['Data']}';
    Uint8List compressed = base64.decode(zipText);
    var gzipBytes = new GZipDecoder().decodeBytes(compressed);

    // Decode List<int> to String
    var stringDecoded = utf8.decode(gzipBytes);
    debugPrint('decoded: $stringDecoded');

    setState(() {
      _textEditingControllerEncode.text = stringDecoded;
      _textEditingControllerDecode.clear();
    });
  }
}