new_sb.dart

import 'package:flutter/widgets.dart';
import 'new_sb_base.dart';

class MyStreamBuilder<T> extends MyStreamBuilderBase<T, AsyncSnapshot<T>> {
  /// Creates a new [MyStreamBuilder] that builds itself based on the latest
  /// snapshot of interaction with the specified [stream] and whose build
  /// strategy is given by [builder].
  ///
  /// The [initialData] is used to create the initial snapshot.
  ///
  /// The [builder] must not be null.
  const MyStreamBuilder({
    Key key,
    this.initialData,
    Stream<T> stream,
    @required this.builder,
  }) : assert(builder != null),
        super(key: key, stream: stream);

  /// The build strategy currently used by this builder.
  ///
  /// This builder must only return a widget and should not have any side
  /// effects as it may be called multiple times.
  final AsyncWidgetBuilder<T> builder;

  /// The data that will be used to create the initial snapshot.
  ///
  /// Providing this value (presumably obtained synchronously somehow when the
  /// [Stream] was created) ensures that the first frame will show useful data.
  /// Otherwise, the first frame will be built with the value null, regardless
  /// of whether a value is available on the stream: since streams are
  /// asynchronous, no events from the stream can be obtained before the initial
  /// build.
  final T initialData;

  @override
  AsyncSnapshot<T> initial() => AsyncSnapshot<T>.withData(ConnectionState.none, initialData);

  @override
  AsyncSnapshot<T> afterConnected(AsyncSnapshot<T> current) => current.inState(ConnectionState.waiting);

  @override
  AsyncSnapshot<T> afterData(AsyncSnapshot<T> current, T data) {
    return AsyncSnapshot<T>.withData(ConnectionState.active, data);
  }

  @override
  AsyncSnapshot<T> afterError(AsyncSnapshot<T> current, Object error) {
    return AsyncSnapshot<T>.withError(ConnectionState.active, error);
  }

  @override
  AsyncSnapshot<T> afterDone(AsyncSnapshot<T> current) => current.inState(ConnectionState.done);

  @override
  AsyncSnapshot<T> afterDisconnected(AsyncSnapshot<T> current) => current.inState(ConnectionState.none);

  @override
  Widget build(BuildContext context, AsyncSnapshot<T> currentSummary) => builder(context, currentSummary);
}