presenting-streams-in-flutter.dart

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import 'package:flutter/material.dart';

void main() {
  runApp(
    const App(),
  );
}

class App extends StatelessWidget {
  const App({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark(),
      debugShowCheckedModeBanner: false,
      home: const HomePage(),
    );
  }
}

extension 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, 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:
      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 {
          return onDoneWitNeitherDataNorError?.call(context) ??
              const SizedBox.shrink();
        }
    }
  }
}

Stream<String> getDateTime() => Stream.periodic(
      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, Object error, StackTrace stackTrace)? onError,
    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),
        ),
      ),
    );
  }
}