Flutter中RangeError(index)异常排查：空列表索引0访问问题

错误日志 #

[错误:flutter/lib/ui/ui_dart_state.cc(198)] 未处理异常：RangeError (索引)：无效值：有效取值范围为空：0
E/flutter (11420): #0 List.[] (dart:core-patch/growable_array.dart:264:36)
E/flutter (11420): #1 LocationService.getPlaceId (package:ridesharingv1/models/location_service.dart:15:37)

相关代码 #

import 'dart:convert' as convert;

import 'package:http/http.dart' as http;

class LocationService {
  // LocationService();
  final String _apiKey = 'AIza...';

  Future<String> getPlaceId(String input) async {
    final String url =
        'https://maps.googleapis.com/maps/api/place/findplacefromtext/json?input=$input&inputted=textquery&fields=place_id&key=$_apiKey';
    var response = await http.get(Uri.parse(url));
    // if (response.statusCode == 200) {
    var json = convert.jsonDecode(response.body);
    var placeId = json['candidates'][0]['place_id'] as String;
    print(placeId);
    return placeId;
    // } else {
    //   throw Exception('Failed to load place id');
    // }
  }

  // Future<Map<String, dynamic>> getPlace(String input) async {
  //   final placeId = await getPlace(input);
  //   final String url =
  //       'https://maps.googleapis.com/maps/api/place/details/json?place_id=$placeId&fields=name,formatted_address,geometry&key=$_apiKey';
  //   var response = await http.get(Uri.parse(url));
  //
  //   // if (response.statusCode == 200) {
  //   final json = convert.jsonDecode(response.body);
  //
  //   var result = json['result'] as Map<String, dynamic>;
  //   print(result);
  //   return result;
  //   // } else {
  //   //   throw Exception('Failed to load place');
  //   // }
  // }
}

问题描述 #

在Flutter项目中调用Google Places API获取place_id时触发RangeError(index)异常，原因是代码直接访问json['candidates'][0]，未判断candidates列表是否为空，当请求返回的候选结果为空时就会出现该异常。

解决方案 #

从边界判断、HTTP状态校验、异常捕获三个层面优化代码即可解决问题：

• 添加候选结果空判断：在访问candidates[0]前，先检查json['candidates']是否为非空列表，避免索引越界
• 恢复HTTP状态码校验：处理非200状态的请求，覆盖请求失败、API限流等场景
• 添加异常捕获：捕获JSON解析、API请求中的异常，返回更明确的错误提示
• 修正URL参数错误：原URL中inputted是拼写错误，正确参数为inputtype，该错误也可能导致返回空结果

优化后的代码如下：

import 'dart:convert' as convert;

import 'package:http/http.dart' as http;

class LocationService {
  final String _apiKey = 'AIza...';

  Future<String> getPlaceId(String input) async {
    final String url =
        'https://maps.googleapis.com/maps/api/place/findplacefromtext/json?input=$input&inputtype=textquery&fields=place_id&key=$_apiKey';
    try {
      var response = await http.get(Uri.parse(url));
      
      // 校验HTTP请求状态
      if (response.statusCode != 200) {
        throw Exception('请求失败，状态码：${response.statusCode}');
      }

      var json = convert.jsonDecode(response.body);
      // 检查candidates列表是否存在且非空
      if (json['candidates'] == null || (json['candidates'] as List).isEmpty) {
        throw Exception('未找到匹配的地点，请检查输入内容');
      }

      var placeId = json['candidates'][0]['place_id'] as String;
      print(placeId);
      return placeId;
    } catch (e) {
      print('获取place_id失败：$e');
      rethrow; // 向上抛出异常，让调用方处理
    }
  }
}

内容的提问来源于stack exchange，提问作者Nabaraj Bhandari