嵌套

A widget that simplifies the syntax for deeply nested widget trees.

Motivation

Widgets tend to get pretty nested rapidly. It's not rare to see:

MyWidget(
  child: AnotherWidget(
    child: Again(
      child: AndAgain(
        child: Leaf(),
      )
    )
  )
)

That's not very ideal.

There's where nested propose a solution. Using nested, it is possible to flatten the previous tree into:

Nested(
  children: [
    MyWidget(),
    AnotherWidget(),
    Again(),
    AndAgain(),
  ],
  child: Leaf(),
),

That's a lot more readable!

Usage

Nested relies on a new kind of widget: SingleChildWidget, which has two concrete implementation:

• SingleChildStatelessWidget
• SingleChildStatefulWidget

These are SingleChildWidget variants of the original Stateless/StatefulWidget.

The difference between a widget and its single-child variant is that they have a custom build method that takes an extra parameter.

As such, a StatelessWidget would be:

class MyWidget extends StatelessWidget {
  MyWidget({Key key, this.child}): super(key: key);

  final Widget child;

  @override
  Widget build(BuildContext context) {
    return SomethingWidget(child: child);
  }
}

Whereas a SingleChildStatelessWidget would be:

class MyWidget extends SingleChildStatelessWidget {
  MyWidget({Key key, Widget child}): super(key: key, child: child);

  @override
  Widget buildWithChild(BuildContext context, Widget child) {
    return SomethingWidget(child: child);
  }
}

This allows our new MyWidget to be used both with:

MyWidget(
  child: AnotherWidget(),
)

and to be placed inside children of [Nested] like so:

Nested(
  children: [
    MyWidget(),
    ...
  ],
  child: AnotherWidget(),
)