RangeError（index）：无效值：有效值范围为空：0

Question

Widget build(context) {
    try{
      if (isFirst == true) {
        fetchImage();
        fetchCategories(context);
        isFirst = false;
      }
    }catch(Exception){

    }

    return MaterialApp(
      home: Scaffold(
        backgroundColor: Colors.black,
        appBar: AppBar(
          title: Text('Lets see images!'),
        ),
        body: new Column(
          children: <Widget>[
            new Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                new InkResponse(
                    child: new Column(
                      children: <Widget>[
                        Padding(
                          padding: EdgeInsets.all(10.0),
                          child: new Image.asset(
                            catimages[0],
                            width: 60.0,
                            height: 60.0,
                          ),
                        ),
                        new Text(
                          categoriesText[0],
                          style: TextStyle(color: Colors.white),
                        ),
                      ],
                    ),
                    onTap: () {
                      debugPrint("on tv clikced");
                      widget.fetchApI.fetchSubCategories(context, 6);
                    }),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset(
                          catimages[1],
                          width: 60.0,
                          height: 60.0,
                        ),
                      ),
                      new Text(
                        categoriesText[1],
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint("on moview clicked");
                    widget. fetchApI.fetchSubCategories(context, 7);
                  },
                ),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset(
                          catimages[2],
                          width: 60.0,
                          height: 60.0,
                        ),
                      ),
                      new Text(
                       categoriesText[2],
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint("on news clicked");
                    widget.fetchApI.fetchSubCategories(context, 10);
                  },
                ),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset(catimages[3],
                            width: 60.0, height: 60.0),
                      ),
                      new Text(
                        categoriesText[3],
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint('on shows clicked');
                    widget.fetchApI.fetchSubCategories(context, 8);
                  },
                ),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset('assets/live_icon.png',
                            width: 60.0, height: 60.0),
                      ),
                      new Text(
                        'Live',
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint('on live clicked');
                  },
                ),
              ],
            ),
            ImageList(images,widget.fetchApI),
          ],
        ),
      ),
    );
  }

我试图从API获取列表，这是两个方法fetchImages和fetchCategories。第一次显示红屏错误，然后在2秒后自动加载列表。你可以告诉我我的代码的问题以及如何避免在我的应用程序中显示红屏错误。

Answer 1

如果您从API获取数据，请考虑使用FutureBuilder。

Answer 2

有快速和肮脏的答案，以及正确的答案

Quick-and-dirty

使用list?.elementAt(<index>) ?? ""安全访问列表元素

Widget build(context) {
    try{
      if (isFirst == true) {
        fetchImage();
        fetchCategories(context);
        isFirst = false;
      }
    }catch(Exception){

    }

    return MaterialApp(
      home: Scaffold(
        backgroundColor: Colors.black,
        appBar: AppBar(
          title: Text('Lets see images!'),
        ),
        body: new Column(
          children: <Widget>[
            new Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                new InkResponse(
                    child: new Column(
                      children: <Widget>[
                        Padding(
                          padding: EdgeInsets.all(10.0),
                          child: new Image.asset(
                            catimages?.elementAt(0) ?? "",
                            width: 60.0,
                            height: 60.0,
                          ),
                        ),
                        new Text(
                          categoriesText?.elementAt(0) ?? "",
                          style: TextStyle(color: Colors.white),
                        ),
                      ],
                    ),
                    onTap: () {
                      debugPrint("on tv clikced");
                      widget.fetchApI.fetchSubCategories(context, 6);
                    }),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset(
                          catimages?.elementAt(1) ?? "",
                          width: 60.0,
                          height: 60.0,
                        ),
                      ),
                      new Text(
                        categoriesText?.elementAt(1) ?? "",
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint("on moview clicked");
                    widget. fetchApI.fetchSubCategories(context, 7);
                  },
                ),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset(
                          catimages?.elementAt(2) ?? "",
                          width: 60.0,
                          height: 60.0,
                        ),
                      ),
                      new Text(
                       categoriesText?.elementAt(2) ?? "",
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint("on news clicked");
                    widget.fetchApI.fetchSubCategories(context, 10);
                  },
                ),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset(catimages?.elementAt(3) ?? "",
                            width: 60.0, height: 60.0),
                      ),
                      new Text(
                        categoriesText?.elementAt(3) ?? "",
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint('on shows clicked');
                    widget.fetchApI.fetchSubCategories(context, 8);
                  },
                ),
                new InkResponse(
                  child: new Column(
                    children: <Widget>[
                      Padding(
                        padding: EdgeInsets.all(10.0),
                        child: new Image.asset('assets/live_icon.png',
                            width: 60.0, height: 60.0),
                      ),
                      new Text(
                        'Live',
                        style: TextStyle(color: Colors.white),
                      ),
                    ],
                  ),
                  onTap: () {
                    debugPrint('on live clicked');
                  },
                ),
              ],
            ),
            ImageList(images,widget.fetchApI),
          ],
        ),
      ),
    );
  }
}

Proper answer

坦率地说，如果我要查看这段代码，即使它无缝地工作，我也会拒绝这种改变，因为这段代码使用的结构/模式非常糟糕。

请使用FutureBuilder，StreamBuilder或ValueListenableBuilder代替，但您需要提供更多代码（尤其是fetchImage和fetchCategories）供我们帮助。