[Bug]: `ObservableAsPropertyHelper` emits property changed for lazy initial value after first-time reading and doesn't respect `DistinctUntilChanged`

[AmrAlSayed0]

Describe the bug 🐞

When reading a calculated property backed by a lazy ObservableAsPropertyHelper an INPC event is emitted while the value of the property is still the initial value which is not the case for normal properties.

There is also another bug that if the emitted non-initial value is the same as the initial value it is still emmitted.

Step to reproduce

public sealed class SuperDuperReactiveObject : ReactiveObject
{
	private readonly ObservableAsPropertyHelper<string?> _calculatedPropertyLazyOaph;
	private readonly ObservableAsPropertyHelper<string?> _calculatedPropertyEagerOaph;

	public string? CalculatedPropertyLazy => this._calculatedPropertyLazyOaph.Value;
	public string? CalculatedPropertyEager => this._calculatedPropertyEagerOaph.Value;

	[Reactive]
	public string? ReactiveStringObject { get; set; }

	public SuperDuperReactiveObject(IObservable<string?> calculatedPropertyObs, bool useInternalProperty)
	{
		if (useInternalProperty)
		{
			IObservable<string?> reactiveStringObjectObs = this.WhenAnyValue(vm => vm.ReactiveStringObject);
			this._calculatedPropertyLazyOaph = reactiveStringObjectObs.ToProperty(this, nameof(SuperDuperReactiveObject.CalculatedPropertyLazy), (string?)null, true);
			this._calculatedPropertyEagerOaph = reactiveStringObjectObs.ToProperty(this, nameof(SuperDuperReactiveObject.CalculatedPropertyEager), (string?)null, false);
		}
		else
		{
			this._calculatedPropertyLazyOaph = calculatedPropertyObs.ToProperty(this, nameof(SuperDuperReactiveObject.CalculatedPropertyLazy), (string?)null, true);
			this._calculatedPropertyEagerOaph = calculatedPropertyObs.ToProperty(this, nameof(SuperDuperReactiveObject.CalculatedPropertyEager), (string?)null, false);
		}
	}
}

Case 1

Code

Subject<string?> subject = new Subject<string?>();

SuperDuperReactiveObject ro = new SuperDuperReactiveObject(subject, false);

ro.Changed.Subscribe(e => Debug.WriteLine($"{e.PropertyName} Changed to {e.Sender?.GetType()?.GetProperty(e.PropertyName!)?.GetMethod?.Invoke(e.Sender, Array.Empty<object>())}"));

Debug.WriteLine($"Before Sending a source change");

subject.OnNext("First");

Debug.WriteLine($"After Sending a source change");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Reading Properties");

string? calculatedPropertyLazy = ro.CalculatedPropertyLazy;
string? calculatedPropertyEager = ro.CalculatedPropertyEager;

Debug.WriteLine($"After Reading Properties");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Sending a 2nd source change");

subject.OnNext("Second");

Debug.WriteLine($"After Sending a 2nd source change");

Result

Before Sending a source change
CalculatedPropertyEager Changed to First            //As expected
After Sending a source change

Before Reading Properties
CalculatedPropertyLazy Changed to             //Expected nothing here
After Reading Properties

Before Sending a 2nd source change
CalculatedPropertyEager Changed to Second            //As expected
CalculatedPropertyLazy Changed to Second            //As expected
After Sending a 2nd source change

Case 2

Code

Subject<string?> subject = new Subject<string?>();

SuperDuperReactiveObject ro = new SuperDuperReactiveObject(subject, false);

ro.Changed.Subscribe(e => Debug.WriteLine($"{e.PropertyName} Changed to {e.Sender?.GetType()?.GetProperty(e.PropertyName!)?.GetMethod?.Invoke(e.Sender, Array.Empty<object>())}"));

Debug.WriteLine($"Before Sending a source change");

subject.OnNext(null);

Debug.WriteLine($"After Sending a source change");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Reading Properties");

string? calculatedPropertyLazy = ro.CalculatedPropertyLazy;
string? calculatedPropertyEager = ro.CalculatedPropertyEager;

Debug.WriteLine($"After Reading Properties");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Sending a 2nd source change");

subject.OnNext(null);

Debug.WriteLine($"After Sending a 2nd source change");

Result

Before Sending a source change
After Sending a source change

Before Reading Properties
CalculatedPropertyLazy Changed to             //Expected nothing here
After Reading Properties

Before Sending a 2nd source change
CalculatedPropertyLazy Changed to             //Expected nothing here
After Sending a 2nd source change

Case 3

Code

Subject<string?> subject = new Subject<string?>();

SuperDuperReactiveObject ro = new SuperDuperReactiveObject(subject, true);

ro.Changed.Subscribe(e => Debug.WriteLine($"{e.PropertyName} Changed to {e.Sender?.GetType()?.GetProperty(e.PropertyName!)?.GetMethod?.Invoke(e.Sender, Array.Empty<object>())}"));

Debug.WriteLine($"Before Sending a source change");

ro.ReactiveStringObject = "First";

Debug.WriteLine($"After Sending a source change");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Reading Properties");

string? calculatedPropertyLazy = ro.CalculatedPropertyLazy;
string? calculatedPropertyEager = ro.CalculatedPropertyEager;

Debug.WriteLine($"After Reading Properties");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Sending a 2nd source change");

ro.ReactiveStringObject = "Second";

Debug.WriteLine($"After Sending a 2nd source change");

Result

Before Sending a source change
CalculatedPropertyEager Changed to First            //As expected
ReactiveStringObject Changed to First            //As expected
After Sending a source change

Before Reading Properties
CalculatedPropertyLazy Changed to             //Expected nothing here
CalculatedPropertyLazy Changed to First            //As expected
After Reading Properties

Before Sending a 2nd source change
CalculatedPropertyEager Changed to Second            //As expected
ReactiveStringObject Changed to Second            //As expected
CalculatedPropertyLazy Changed to Second            //As expected
After Sending a 2nd source change

Case 4

Code

Subject<string?> subject = new Subject<string?>();

SuperDuperReactiveObject ro = new SuperDuperReactiveObject(subject, true);

ro.Changed.Subscribe(e => Debug.WriteLine($"{e.PropertyName} Changed to {e.Sender?.GetType()?.GetProperty(e.PropertyName!)?.GetMethod?.Invoke(e.Sender, Array.Empty<object>())}"));

Debug.WriteLine($"Before Sending a source change");

ro.ReactiveStringObject = null;

Debug.WriteLine($"After Sending a source change");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Reading Properties");

string? calculatedPropertyLazy = ro.CalculatedPropertyLazy;
string? calculatedPropertyEager = ro.CalculatedPropertyEager;

Debug.WriteLine($"After Reading Properties");
Debug.WriteLine(string.Empty);

Debug.WriteLine($"Before Sending a 2nd source change");

ro.ReactiveStringObject = null;

Debug.WriteLine($"After Sending a 2nd source change");

Result

Before Sending a source change
After Sending a source change

Before Reading Properties
CalculatedPropertyLazy Changed to             //Expected nothing here
CalculatedPropertyLazy Changed to             //Expected nothing here
After Reading Properties

Before Sending a 2nd source change
After Sending a 2nd source change

Reproduction repository

Code is inline

Expected behavior

Included in the comments in the "Steps to reproduce"

IDE

Visual Studio 2022

Operating system

Windows

Device

Windows PC

ReactiveUI Version

19.5.1

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