What does Underscore "_" before variable name mean for Flutter

with reference to the Flutter tutorial, I encountered an underscore, _.

I know that in Java, _ is used as a naming convention for a private variable.

Does it also apply to Flutter? Noting that there is no public/protected in Flutter.
Will the _ really be private (inaccessible by other classes) or is it just a naming convention?

Variable

class RandomWordsState extends State<RandomWords> {
final List<WordPair> _suggestions = <WordPair>[];
final Set<WordPair> _saved = new Set<WordPair>();
final TextStyle _biggerFont = const TextStyle(fontSize: 18.0);
...
}

Does the _ make the Widget private too? In this case, wouldn't the main class be unable to assess the Widget?

Function

Widget _buildRow(WordPair pair) {
final bool alreadySaved = _saved.contains(pair);  // Add this line.
...
}

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From the Dart guide

Unlike Java, Dart doesn’t have the keywords public, protected, and private. If an identifier starts with an underscore (_), it’s private to its library. For details, see Libraries and visibility.

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最佳答案

It's not just a naming convention. Underscore fields, classes and methods will only be available in the .dart file where they are defined.

It is common practice to make the State implementation of a widget private, so that it can only be instantiated by the corresponding StatefulWidget:

class MyPage extends StatefulWidget {
@override
_MyPageState createState() => _MyPageState();
}


class _MyPageState extends State<MyPage> {
@override
Widget build(BuildContext context) {
return Container();
}
}

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Private fields also have the advantage that Lint can identify which fields were declared/instantiated and not used, which helps identify human errors.

If you declare a public field, the field may be accessed by classes outside the class in the future and so Lint cannot warn you if you added the field by mistake.