fragment 0.0.1

Easily prevent unnecessary build() calls in StatefulWidget and its subtrees.

fragment

Easily prevent unnecessary build() calls in StatefulWidget and its subtrees.

If you know React, you may consider this as a shouldComponentUpdate alternate for Flutter.

Getting Started

The library comes with a Mixin, Fragments, which you can add to your State.

class FragmentContainer extends StatefulWidget {
  final int key1;
  final int key2;
  final int key3;

  const FragmentContainer( {Key key, this.key1, this.key2, this.key3}) : super(key: key);

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

class _FragmentContainerState extends State<FragmentContainer> with Fragments {
  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        fragment(() => Container(), [widget.key1]),
        fragment(() => Container(), [widget.key2]),
        fragment(() => Container(), [widget.key3]),
      ],
    );
  }
}

When one of key1, key2 and key3 updates, the other two Containers in other lines won't be recreated.

fragment method takes two parameters: a factory function which returns the target Widget, and an Iterable to determine when to call the factory. During each call, the second parameter is compared with the second parameter in previous call. If they are shallowly equal, the factory will be ignored and the return value from previous factory function is used as the return value of fragment, otherwise, the factory function is called and its return value is returned by fragment.

All fragment calls' order must be consistent across different passes of builds, so please be careful when using fragment in loops and conditionals.