Flutter：RangeError（索引）：无效值：不在0..14范围内，包括：15

Posted 2023-02-23

【中文标题】Flutter：RangeError（索引）：无效值：不在0..14范围内，包括：15

【英文标题】：Flutter: RangeError (index): Invalid value: Not in range 0..14, inclusive: 15

【发布时间】：2020-06-30 20:09:07

【问题描述】：

我正在使用 bloc 设计模式和 (flutter_bloc lib) 构建一个 ListView，当只放置列表长度并返回小部件时，列表是分页的并且工作正常，

但是当我尝试在列表中添加一个指示器并为 itemCount 添加 + 1 以加载 UI 时，就会出现问题

错误

Restarted application in 1,900ms.

[38;5;248m════════ Exception caught by widgets library ═══════════════════════════════════[39;49m
[38;5;244mThe following RangeError was thrown building:[39;49m
RangeError (index): Invalid value: Not in range 0..14, inclusive: 15

[38;5;244mWhen the exception was thrown, this was the stack[39;49m
[38;5;244m#0      List.[]  (dart:core-patch/growable_array.dart:149:60)[39;49m
[38;5;248m#1      _HomePageState.build.<anonymous closure>.<anonymous closure>[39;49m
[38;5;244m#2      SliverChildBuilderDelegate.build[39;49m
[38;5;244m#3      SliverMultiBoxAdaptorElement._build.<anonymous closure>[39;49m
[38;5;244m#4      _HashMap.putIfAbsent  (dart:collection-patch/collection_patch.dart:139:29)[39;49m
[38;5;244m...[39;49m
[38;5;248m════════════════════════════════════════════════════════════════════════════════[39;49m

列表代码

return BlocListener<PostsBloc, PostsState>(
  listener: (context, state) 
    if ( state is PostsError ) 
      Scaffold.of(context).showSnackBar(
        SnackBar(content: Text(state.errMsg))
      );
    
  ,        
  child: BlocBuilder<PostsBloc, PostsState>(builder: (context, state) 
    if (state is PostsInitial || state is PostsLoading) 
      return loading();
     else if (state is PostsLoaded) 
      return ListView.builder(
        itemCount: state.hasReachedMax
            ? state.posts.length
            : state.posts.length + 1,
        controller: _scrollController,
        itemBuilder: (BuildContext context, int i) 
          final Post post = state.posts[i];

          return (i >= state.posts.length) 
          ? Center(child: CircularProgressIndicator())
          : ListTile(leading: Text(i.toString()), title: Text(post.title, style: TextStyle(fontWeight: FontWeight.bold),));
        
      );
    

    return errorMsg();
  ),
);

【参考方案1】：

首先检查长度。如果数组不会超出范围，则仅尝试使用 final Post post = state.posts[i];

访问该元素

没试过，但我希望这对你有用。

itemBuilder: (BuildContext context, int i) 
          if(i >= state.posts.length)
            return Center(child: CircularProgressIndicator());
          
          final Post post = state.posts[i];
          ListTile(leading: Text(i.toString()), title: Text(post.title, style: TextStyle(fontWeight: FontWeight.bold),));
        
```

【讨论】：

它就像一个魅力，非常感谢，但我不明白我的代码有什么问题以及你和我的区别

如果 i>=length，我的代码不会到达 state.posts[i] 这一行。但你的。如果它对您有用，请接受答案。 :)

完成，感谢您的澄清