Confusion about migrating from ReactiveProperty

[maonaoda]

I knew that R3 it the next ReactiveProperty,

Since there are no ObserveHasErrors, How do I need to express it using R3? It that Password.ErrorsChanged ? PasswordHasError = Password.ObserveHasErrors.CombineLatest(PasswordUnfocused, (x, y) => x && y).ToReactiveProperty().AddTo(Disposables);

※There is also ObserveValidationErrorMessage

[neuecc]

BindableReactiveProperty provides ErrorsChanged event. This is an event for XAML Binding, but can also be subscribed to manually. If you want to operate with Rx, you can convert this as a FromEvent.

[maonaoda]

@neuecc Hi, I am using Maui,

Is that be subscribed manually like this?

            Password = new BindableReactiveProperty<string>(string.Empty).EnableValidation(() => Password);
            PasswordHasError =
                Observable.EveryValueChanged(Password, x => x.HasErrors)
                .ToBindableReactiveProperty();
            PasswordErrorMessage =
                Observable.EveryValueChanged(Password, x => Password.GetErrors(null).OfType<ValidationResult>()?.FirstOrDefault()?.ErrorMessage)
                .ToBindableReactiveProperty();

---

ReactiveProperty`s using:

            Password = new ReactiveProperty<string>(string.Empty).SetValidateAttribute(() => Password).AddTo(Disposables);
            PasswordHasError = Password.ObserveHasErrors.ToReactiveProperty().AddTo(Disposables);
            PasswordErrorMessage = Password.ObserveValidationErrorMessage().ToReactiveProperty().AddTo(Disposables);

[neuecc]

First, R3 is not intended to port the full functionality of ReactiveProperty (more like ReactivePropertySlim, if anything). If that works, then it's good.

[maonaoda]

I added this method for myself. Thanks for your guidance.

    public static class BindableReactivePropertyExtensions
    {
        public static Observable<bool> ObserveHasErrors<T>(this BindableReactiveProperty<T> source)
        {
            return Observable.EveryValueChanged(source, x => x.HasErrors);
        }

        public static Observable<string?> ObserveValidationErrorMessage<T>(this BindableReactiveProperty<T> source)
        {
            return Observable.EveryValueChanged(source, x => x.GetErrors(null)?.OfType<ValidationResult>()?.FirstOrDefault()?.ErrorMessage);
        }
    }

[maonaoda]

The above code is constantly executing, and I changed it to this （FromEvent）. There are slight differences of the actual action with ReactiveProperty, but it does not affect the final effect.

Although BindableReactivePropertysHasErrorsorGetErrors` can be used directly in Xaml, other processing is required in our app.

            PasswordHasError = Password.ErrorsChangedAsObservable()
                .CombineLatest(PasswordUnfocused, (_, y) => (Password.HasErrors && y))
                .ToBindableReactiveProperty();
            PasswordErrorMessage = Password.ErrorsChangedAsObservable().Select(_ => Password.GetErrorMessage())
                .ToBindableReactiveProperty();

        public static Observable<(object? sender, DataErrorsChangedEventArgs e)> ErrorsChangedAsObservable<T>(this BindableReactiveProperty<T> source)
        {
            return Observable.FromEventHandler<DataErrorsChangedEventArgs>(handler => source.ErrorsChanged += handler,
                handler => source.ErrorsChanged -= handler).AsObservable();
        }

        public static string? GetErrorMessage<T>(this BindableReactiveProperty<T> source)
        {
            return source.GetErrors(null)?.OfType<ValidationResult>()?.FirstOrDefault()?.ErrorMessage;
        }

[maonaoda]

Since R3 v1.1.1 released, I changed to ObservePropertyChanged to migrate form ReactiveProperty, Because DataErrorsChangedEvent just is ErrorsChangedEvent.

        public static Observable<bool> ObserveHasErrors<T>(this BindableReactiveProperty<T> source)
        {
            return source.ObservePropertyChanged(x => x.Value)
                .Select(_ => source.HasErrors);
        }

        public static Observable<string?> ObserveValidationErrorMessage<T>(this BindableReactiveProperty<T> source)
        {
            return source.ObservePropertyChanged(x => x.Value)
                .Select(_ => source.GetErrorMessage());
        }

        private static string? GetErrorMessage<T>(this BindableReactiveProperty<T> source)
        {
            return source.GetErrors(null)?.OfType<ValidationResult>()?.FirstOrDefault()?.ErrorMessage;
        }

[maonaoda]

May be v1.1.2 fixed Errors`s disappeance, that I can use FromEventHandler again ?

[maonaoda]

May be v1.1.2 fixed Errors`s disappeance, that I can use FromEventHandler again ?

Thats right, use FromEventHandler instead of ObservePropertyChanged, since that ObservePropertyChanged will handel every value changed.

[maonaoda]

@neuecc

One more thing. Because CombineLatest has the check of Value existence, when I use FromEventHandler like ↓, Unless calling Password.ForceNotify(); manually after，the using of FromEventHandler will not have value at the first time. and CombineLatest will not be excuted for the first time.

            PasswordHasError = Password
                //.ErrorsChangedAsObservable()
                .ObserveHasErrors()
                .CombineLatest(PasswordUnfocused, (_, y) => (Password.HasErrors && y))
                .ToBindableReactiveProperty();

(https://github.com/Cysharp/R3/blob/b72a8d8a8761908b903353fbe5a9cce5168f30c5/src/R3/Operators/CombineLatest.cs#L281-L297)

[neuecc]

you ca use Prepend for initial value

[maonaoda]

Prepend is OK.

        public static Observable<bool> ObserveHasErrors<T>(this BindableReactiveProperty<T> source)
        {
            return source
                .ErrorsChangedAsObservable()
                //.ObservePropertyChanged(x => x.Value)
                .Select(_ => source.HasErrors)
                .Prepend(true);
        }

        public static Observable<string?> ObserveValidationErrorMessage<T>(this BindableReactiveProperty<T> source, string defaultError)
        {
            return source
                .ErrorsChangedAsObservable()
                //.ObservePropertyChanged(x => x.Value)
                .Select(_ => source.GetErrorMessage())
                .Prepend(defaultError);
        }

[maonaoda]

Prepend is OK.

Take back this statement as .Prepend(defaultError); won`t set inner errors. so previouslyHasErrors is false, but i want it is true.

reuse ForceNotify() finally~