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extension NoteStateX on NoteState {
  /// Checks if a note in this state can be edited.
  bool get canEdit => this < NoteState.deleted;

  /// Returns true if this state is preceding to the other one.
  bool operator <(NoteState other) => (this?.index ?? 0) < (other?.index ?? 0);

  /// Message describes the state transition.
  String get message {
    switch (this) {      

xinthink

/// Save the note before the editor is dismissed
Future<dynamic> _onPop(String uid) => _isDirty
  ? _note.saveToFireStore(uid)
  : Future.value();

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extension NoteStore on Note {
  /// Save this note to FireStore.
  Future<dynamic> saveToFireStore(String uid) async {
    final col = notesCollection(uid);
    return id == null
      ? col.add(toJson())
      : col.document(id).updateData(toJson());
  }
    ...
}

xinthink

class _HomeScreenState extends State<HomeScreen> with CommandHandler {
  Widget _fab(BuildContext context) => FloatingActionButton(
    child: const Icon(Icons.add),
    onPressed: () async {
      final command = await Navigator.pushNamed(context, '/note');
      processNoteCommand(_scaffoldKey.currentState, command);
    },
  );
  ...
}

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mixin CommandHandler<T extends StatefulWidget> on State<T> {
  /// Processes the given [command].
  Future<void> processNoteCommand(ScaffoldState scaffoldState, NoteCommand command) async {
    if (command == null) {
      return;
    }
    await command.execute();
    final msg = command.message;
    if (mounted && msg?.isNotEmpty == true) {
      scaffoldState?.showSnackBar(SnackBar(

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@override
Widget build(BuildContext context) {
  final uid = Provider.of<CurrentUser>(context).data.uid;
  return ChangeNotifierProvider.value(
    value: _note,
    child: Consumer<Note>(
      builder: (_, __, ___) => Hero(
        tag: 'NoteItem${_note.id}',
        child: DefaultTextStyle(
          style: ...

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// in the note list
@override
Widget build(BuildContext context) => Hero(
  tag: 'NoteItem${note.id}',
  child: DefaultTextStyle(
    style: kNoteTextLight,
    child: Container(            
      ...
    ),
  ),

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// when pressed, dissmiss the bottom sheet and return a command
IconButton(
  icon: const Icon(Icons.archive),
  tooltip: 'Archive',
  onPressed: () => Navigator.pop(context, NoteStateUpdateCommand(
    id: _note.id,
    uid: uid,
    from: _note.state, // the current state
    to: NoteState.archived, // the transition target
  )),

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class NoteStateUpdateCommand extends NoteCommand {
  final NoteState from;
  final NoteState to;

  /// Create a [NoteCommand] to update state of a note [from] the current state [to] another.
  NoteStateUpdateCommand({
    @required String id,
    @required String uid,
    @required this.from,
    @required this.to,

xinthink

abstract class NoteCommand {
  final String id;
  final String uid;

  /// Defines an reversible action to a note, provides the note [id], and the current user's [uid].
  const NoteCommand({
    @required this.id,
    @required this.uid,
  });