OAPH requires setting _nameHelper

[stokara]

Following the docs I tried:

[ObservableAsProperty]
public partial Type SearchTermType { get; }
...
this.WhenAnyValue(x => x.SelectedProperty)
            .WhereNotNull()
            .Select(p => p.Type)
            .ToProperty(this, x => x.SearchTermType);

but when getting to code that references SearchTermType it is null;

however, this code, referencing the generated code backing OAPH field does work:

 _searchTermTypeHelper = this.WhenAnyValue(x => x.SelectedProperty)
     .WhereNotNull()
     .Select(p => p.Type)
     .ToProperty(this, x => x.SearchTermType);

this is the using the approach I see in ReactiveGeneratorDemo.ViewModels.OaphViewModel

[CyLuGh]

Have you tried included the out parameter like this:

this.WhenAnyValue(x => x.SelectedProperty)
            .WhereNotNull()
            .Select(p => p.Type)
            .ToProperty(this, x => x.SearchTermType, out _searchTermTypeHelper);

[stokara]

Yes, (that is an alternative directly referencing the generated field) which is not what the documentation describes. The documentation shows using it like the ToPropertyEx method used with Fody. Unless there is another extension method provided I dont see how this can work. Is the documentation wrong?

…

________________________________ From: Jeremy Demortier ***@***.***> Sent: Friday, January 17, 2025 1:36:38 AM To: wieslawsoltes/ReactiveGenerator ***@***.***> Cc: stokara ***@***.***>; Author ***@***.***> Subject: Re: [wieslawsoltes/ReactiveGenerator] OAPH requires setting _nameHelper (Issue #47) Have you tried included the out parameter like this: this.WhenAnyValue(x => x.SelectedProperty) .WhereNotNull() .Select(p => p.Type) .ToProperty(this, x => x.SearchTermType, out _searchTermTypeHelper); — Reply to this email directly, view it on GitHub<#47 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AAIATZSNHGXJYZBFXEYWHKD2LCQHNAVCNFSM6AAAAABVK2WL7OVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKOJXGUZTOMJXGA>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[CyLuGh]

The documentation in the readme and the example in the source (https://github.com/wieslawsoltes/ReactiveGenerator/blob/main/ReactiveGeneratorDemo/ViewModels/OaphViewModel.cs) don't seem to match.

[stokara]

suggestion: Creating a new extension method SetPropertyEx which would set the generated OAPH is not a bad idea as that is the way the Fody implementation works and would make migrating from Fody easier.

e.g.:

this.WhenAnyValue(x => x.SelectedProperty)
.WhereNotNull()
.Select(p => p.Type)
.ToPropertyEx(this, x => x.SearchTermType);

would functionally be:

this.WhenAnyValue(x => x.SelectedProperty)
.WhereNotNull()
.Select(p => p.Type)
.ToProperty(this, x => x.SearchTermType, out _searchTermTypeHelper);

[stokara]

Here is an example extension method .ToPropertyEx - but it uses reflection so it will impact performance.

public static class ReactiveUiExtensions {
    public static IDisposable ToPropertyEx<TObj, TRet>(
        this IObservable<TRet> observable,
        TObj target,
        Expression<Func<TObj, TRet>> property,
        TRet? initialValue = default,
        IScheduler? scheduler = null)
        where TObj : class, IReactiveObject {
        var propertyName = ((MemberExpression) property.Body).Member.Name;
        var fieldName = $"_{char.ToLower(propertyName[0])}{propertyName[1..]}Helper";

        var field = getFieldFromHierarchy(target.GetType(), fieldName);
        if (field == null) {
            throw new InvalidOperationException($"Field '{fieldName}' not found on type '{target.GetType().Name}'.");
        }

        var helper = observable.ToProperty(target, property!, initialValue: initialValue, scheduler: scheduler);
        field.SetValue(target, helper);
        return helper;
    }

    private static FieldInfo? getFieldFromHierarchy(Type? type, string fieldName) {
        while (type != null) {
            var field = type.GetField(fieldName, System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
            if (field != null) return field;
            type = type.BaseType;
        }
        return null;
    }
}

[stokara]

The extension method I suggested above uses reflection and (at least for me) will often be called in the constructor, so I don't like it.

This can be avoided if a "getOaph" method was generated with the generated code, something like this:

        private ObservableAsPropertyHelper<T> GetOaph<T>(Expression<Func<T>> expression)
        {
            var memberExpression = (MemberExpression)expression.Body;
            var fieldName = memberExpression.Member.Name;

            return fieldName switch
            {
                nameof(TestBool) => (ObservableAsPropertyHelper<T>)(object)oaphTestBool,
                _ => throw new ArgumentException("Invalid field name", nameof(expression))
            };
        }

where the "fieldName switch" would contain all of the generated oaph variables