AlexV525 · August 17, 2022 07:54
diff --git a/tri_state.dart b/tri_state.dart
 //
 // [Author] Alex (https://github.com/AlexV525)
 // [Date] 2022/08/17 13:45
 //

 import 'package:flutter/material.dart';

 /// A tri-state indicates the loading process of specific data.
 enum TriState {
  /// The data is still loading, not available.
  loading,

  /// The data has failed to load, not available.
  failed,

  /// The data has loaded successfully, available.
  succeed,
 }

 /// A [ValueNotifier] that holds the [TriState] and [T].
 ///
 /// [state] and [value] will notify listeners when they've changed.
 ///
 /// [T] should be non-nullable since it's an actual/real data.
 class TriStateNotifier<T extends Object> extends ValueNotifier<T?> {
  TriStateNotifier(
    T? data, {
    TriState state = TriState.loading,
  })  : _state = state,
        super(data);

  TriState get state => _state;
  TriState _state;

  set state(TriState newValue) {
    if (_state == newValue) {
      return;
    }
    _state = newValue;
    notifyListeners();
  }

  void successWithData(T data) {
    _state = TriState.succeed;
    value = data;
  }

  void fail() {
    state = TriState.failed;
  }
 }

 /// A widget whose content stays synced with a [TriStateNotifier].
 ///
 /// Given a [TriStateNotifier<T>] and a [dataBuilder] which builds widgets from
 /// concrete values of `T`, this class will automatically register itself as a
 /// listener of the [TriStateNotifier] and call the [dataBuilder] with updated
 /// values when the value changes.
 class TriStateBuilder<T extends Object> extends StatefulWidget {
  /// Creates a [TriStateBuilder].
  const TriStateBuilder({
    Key? key,
    required this.notifier,
    this.stateBuilder,
    this.dataBuilder,
    this.builder,
    this.child,
  })  : assert(
          builder != null || (stateBuilder != null && dataBuilder != null),
          'At least one kind of builders must be specified.',
        ),
        super(key: key);

  /// The [TriStateNotifier] whose value you depend on in order to build.
  ///
  /// This widget does not ensure that the [TriStateNotifier]'s value is not
  /// null, therefore your [builder] may need to handle null values.
  ///
  /// This [notifier] itself must not be null.
  final TriStateNotifier<T> notifier;

  /// A [ValueWidgetBuilder] which builds a widget when the [notifier]'s state
  /// is changing, and not succeed.
  final ValueWidgetBuilder<TriState>? stateBuilder;

  /// A [ValueWidgetBuilder] which builds a widget when the [notifier] succeed
  /// and it's data is not null.
  final ValueWidgetBuilder<T>? dataBuilder;

  /// A builder which builds a widget when the [notifier]'s state or value is
  /// changing, you'll need to handle all cases within the [notifier].
  ///
  /// When the [builder] is not null, all other builder won't have effects.
  final Widget Function(BuildContext, TriState, T?, Widget?)? builder;

  /// A [notifier]-independent widget which is passed back to the [builder].
  final Widget? child;

  @override
  State<TriStateBuilder<T>> createState() => _TriStateBuilderState<T>();
 }

 class _TriStateBuilderState<T extends Object>
    extends State<TriStateBuilder<T>> {
  late TriState state;
  late T? value;

  @override
  void initState() {
    super.initState();
    state = widget.notifier.state;
    value = widget.notifier.value;
    widget.notifier.addListener(_valueChanged);
  }

  @override
  void didUpdateWidget(TriStateBuilder<T> oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.notifier != widget.notifier) {
      oldWidget.notifier.removeListener(_valueChanged);
      state = widget.notifier.state;
      value = widget.notifier.value;
      widget.notifier.addListener(_valueChanged);
    }
  }

  @override
  void dispose() {
    widget.notifier.removeListener(_valueChanged);
    super.dispose();
  }

  void _valueChanged() {
    setState(() {
      state = widget.notifier.state;
      value = widget.notifier.value;
    });
  }

  @override
  Widget build(BuildContext context) {
    if (widget.builder != null) {
      return widget.builder!(context, state, value, widget.child);
    }
    if (state != TriState.succeed) {
      return widget.stateBuilder!(context, state, widget.child);
    }
    return widget.dataBuilder!(context, value!, widget.child);
  }
 }
	//
	// [Author] Alex (https://github.com/AlexV525)
	// [Date] 2022/08/17 13:45
	//

	import 'package:flutter/material.dart';

	/// A tri-state indicates the loading process of specific data.
	enum TriState {
	/// The data is still loading, not available.
	loading,

	/// The data has failed to load, not available.
	failed,

	/// The data has loaded successfully, available.
	succeed,
	}

	/// A [ValueNotifier] that holds the [TriState] and [T].
	///
	/// [state] and [value] will notify listeners when they've changed.
	///
	/// [T] should be non-nullable since it's an actual/real data.
	class TriStateNotifier<T extends Object> extends ValueNotifier<T?> {
	TriStateNotifier(
	T? data, {
	TriState state = TriState.loading,
	}) : _state = state,
	super(data);

	TriState get state => _state;
	TriState _state;

	set state(TriState newValue) {
	if (_state == newValue) {
	return;
	}
	_state = newValue;
	notifyListeners();
	}

	void successWithData(T data) {
	_state = TriState.succeed;
	value = data;
	}

	void fail() {
	state = TriState.failed;
	}
	}

	/// A widget whose content stays synced with a [TriStateNotifier].
	///
	/// Given a [TriStateNotifier<T>] and a [dataBuilder] which builds widgets from
	/// concrete values of `T`, this class will automatically register itself as a
	/// listener of the [TriStateNotifier] and call the [dataBuilder] with updated
	/// values when the value changes.
	class TriStateBuilder<T extends Object> extends StatefulWidget {
	/// Creates a [TriStateBuilder].
	const TriStateBuilder({
	Key? key,
	required this.notifier,
	this.stateBuilder,
	this.dataBuilder,
	this.builder,
	this.child,
	}) : assert(
	builder != null \|\| (stateBuilder != null && dataBuilder != null),
	'At least one kind of builders must be specified.',
	),
	super(key: key);

	/// The [TriStateNotifier] whose value you depend on in order to build.
	///
	/// This widget does not ensure that the [TriStateNotifier]'s value is not
	/// null, therefore your [builder] may need to handle null values.
	///
	/// This [notifier] itself must not be null.
	final TriStateNotifier<T> notifier;

	/// A [ValueWidgetBuilder] which builds a widget when the [notifier]'s state
	/// is changing, and not succeed.
	final ValueWidgetBuilder<TriState>? stateBuilder;

	/// A [ValueWidgetBuilder] which builds a widget when the [notifier] succeed
	/// and it's data is not null.
	final ValueWidgetBuilder<T>? dataBuilder;

	/// A builder which builds a widget when the [notifier]'s state or value is
	/// changing, you'll need to handle all cases within the [notifier].
	///
	/// When the [builder] is not null, all other builder won't have effects.
	final Widget Function(BuildContext, TriState, T?, Widget?)? builder;

	/// A [notifier]-independent widget which is passed back to the [builder].
	final Widget? child;

	@override
	State<TriStateBuilder<T>> createState() => _TriStateBuilderState<T>();
	}

	class _TriStateBuilderState<T extends Object>
	extends State<TriStateBuilder<T>> {
	late TriState state;
	late T? value;

	@override
	void initState() {
	super.initState();
	state = widget.notifier.state;
	value = widget.notifier.value;
	widget.notifier.addListener(_valueChanged);
	}

	@override
	void didUpdateWidget(TriStateBuilder<T> oldWidget) {
	super.didUpdateWidget(oldWidget);
	if (oldWidget.notifier != widget.notifier) {
	oldWidget.notifier.removeListener(_valueChanged);
	state = widget.notifier.state;
	value = widget.notifier.value;
	widget.notifier.addListener(_valueChanged);
	}
	}

	@override
	void dispose() {
	widget.notifier.removeListener(_valueChanged);
	super.dispose();
	}

	void _valueChanged() {
	setState(() {
	state = widget.notifier.state;
	value = widget.notifier.value;
	});
	}

	@override
	Widget build(BuildContext context) {
	if (widget.builder != null) {
	return widget.builder!(context, state, value, widget.child);
	}
	if (state != TriState.succeed) {
	return widget.stateBuilder!(context, state, widget.child);
	}
	return widget.dataBuilder!(context, value!, widget.child);
	}
	}