CODEWITHSUNDEEP
syntaxdartflutter
starleaf1
starleaf1

Reputation: 2872

What is this JSON-like syntax in Flutter's widget constructors?

I'm completely new to Dart and Flutter, and I've been absorbing as much info as possible from docs and tutorials. While Dart itself doesn't trouble me much, Flutter has been difficult so far. For example, I can't seem to wrap my head around this syntax from the Hello World app:

Scaffold(
    appBar: AppBar(
      title: Text('Welcome to Flutter'),
    ),
    // ...
  ),
);

I can't find syntax like it in Dart docs. Is it a constructor, like ClassName(prop1:val1, prop2:val2)?

Upvotes: 1

Views: 106

Answers (2)

jamesdlin
jamesdlin

Reputation: 89965

You're observing Dart's optional named parameters. It's not Flutter-specific.

Upvotes: 1

Onjrew
Onjrew

Reputation: 88

Your intuition is correct. Scafford() is instantiating a Widget (class) constructor, which you can see defined here in the docs.

Flutter UI is a lot of nested constructors like this. Many of the arguments to a Widget's constructor are just, themselves, Widgets.

In your Hello World example the Scaffold Widget's appBar parameter takes an AppBar Widget. The AppBar itself has a parameter named Title which takes a Text Widget.

Upvotes: 2

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