Presenting Streams in Flutter小技巧

extends PresentAsyncSnapshot<E> on AsyncSnapshot<E> {
    Widget present({
        required BuildContext context,
        Widget Function(BuildContext context)? onNone,
        Widget Function(BuildContext context, E data)? onData,
        Widget Function(BuildContext context, Object error, StackTrace stackTrace)? onError,
        Widget Function(BuildContext context)? onDoneWitNeitherDataNorError,
        Widget FUnction(BuildContext context)? onWaiting,
    }) {
        switch (connectionState) {
            case ConnectionState.none:
                return onNone?.call(context) ?? const SizedBox.shrink();
            case ConnectionState.waiting:
                return onWaiting?.call(context) ?? const CircularProgressIndicator();
            case ConnectionState.active: //future在done状态产生值，但是stream在active状态下就已经持续产生值了
            case ConnectionState.done:
                if (hasError) {
                    return onError?.call(context, error!, stackTrace!) ?? const SizedBox.shrink();
                } else if (hasData) {
                    return onData?.call(context, data as E) ?? const SizedBox.shrink();
                } else {
                    reutrn onDoneWitNeitherDataNorError?.call(context) ?? const SizedBox.shrink();
                }
        }
    }
}

Stream<String> getDataTime() => Stream.perioodic(
    const Duration(seconds: 1),
    (_) => DateTime.now().toIso8601string(),
);

extension PresentStream<E> on Stream<E> {
    Widget present({
        Widget Function(BuildContext context)? onNone,
        Widget Function(BuildContext context, E data)? onData,
        Widget Function(BuildContext context, Object error, E data)? onData,
        Widget Function(BuildContext context)? onDoneWitNeitherDataNorError,
        Widget Function(BuildContext context)? onWaiting.
    }) {
        return StreamBuilder<E>(
            stream: this,
            builder: (context, snapshot) => snapshot.present(
                context: context,
                onNone: onNone,
                onData: onData,
                onError: onError,
                onDoneWitNeitherDataNorError: onDoneWItNeitherDataNorError,
                onWaiting: onWaiting,
            ),
        );
    }
}

class HomePage extends StatelessWidget {
    const HomePage({Key? key}): super(key: key);
    @override
    Widget build(BuildContext context) {
        return Scaffold(
            body: SafeArea(
                child: getDateTime().present(
                    onData: (_, dateTime) => Text(dateTime),
                ),
            ),
        );
    }
}