Question

如果可用，我有一个简单的页面呈现信息，否则“未找到”。

数据是从Map<String,Data>取回的，也就是说取错key的数据会导致null。所以我正在检查数据是否为空，然后使用信息。下面的示例代码（下面是完整代码）

我希望 dart 能够识别 if-else 语句，但它没有。我不想添加强制运算符 (data!.text)


final String id = "id";
final Data? data = MyCustomWidget.of(context).info[id];

Widget build(context) {
  if(data != null) {
    //Error: The property 'text' can't be unconditionally
    //accessed because the receiver can be 'null'.
    //Try making the access conditional (using '?.')
    //or adding a null check to the target ('!').

    return Text(data.text);
  }
  return Text("Not Found");
}

完整代码：

class ArtistPage extends StatefulWidget {
  final String id;

  const ArtistPage({Key? key, required this.id}) : super(key: key);

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

class _ArtistPageState extends State<ArtistPage> { 
  late final Data? data;

  @override
  void initState() {
    //App.of(context).info = Map<String,Data>
    data = App.of(context).info[widget.id];
    super.initState();
  }

  @override
  Widget build(BuildContext context) {

    Widget _body() {
      if (data == null) {
        return Text("");
      } else {
        //Simplified
    //Error: The property 'name' can't be unconditionally accessed because the receiver can be 'null'.\nTry making the access conditional (using '?.') or adding a null check to the target ('!').
        return Text(data.name);
      }
    }

    return Scaffold(appBar: AppBar(), body: _body());
  }
}

dart 如何知道是否正确检查了 nullsafety？

0 个答案: