[HxInputDate] [HxInputDateRange] Changing value causes two calls of EditContext.OnFieldChanged

[jirikanda]

Reprosteps

• Handle EditContext.OnFieldChanged event
• Click on a date in the calendar.
• EditContext.OnFieldChanged event handler is called twice

Why?

(both HxInputDate<TValue> and also HxInputDateInternal<TValue> inherit from InputBase<TValue>)

First call

• HxInputDateInternal<TValue>.HandleValueChanged is called.
• HxInputDateInternal<TValue>.HandleValueChanged sets the CurrentValueAsString.
• CurrentValueAsString setter sets InputBase<TValuegt;.CurrentValue.
• InputBase<TValue>.CurrentValue calls ValueChanged (important to understand the the second call)
• The InputBase<TValue>.CurrentValue setter calls EditContext.NotifyFieldChanged for the first time.

Second call

• HxInputDate<Value> handles ValueChanged event
• It sets the CurrentValue property (see BuildRenderInputCore method, sequence number 101).
• The InputBase<TValue>.CurrentValue setter calls (again) EditContext.NotifyFieldChanged.

Posible solutions (not sure right now)

• only HxInputDate<TValue> should derive from InputBase<TValue>
• OR HxInputDate<TValue> should not Set CurrentValue, but it should fire ValueChanged event

(I guess this occurs also in HxInputDateRange while it uses the same code structure.)

[hakenr]

only HxInputDate should derive from InputBase

My preference (same in other similar components).

[jirikanda]

@hakenr, I am not familiar with the current code structure, there for I am not able to fix the issue (until someone explains me the thoughts behind).
ie.

	private void HandleValueChanged(string newInputValue)
	{
#if NET8_0_OR_GREATER
		CurrentValueAsString = newInputValue;
#else
		// HandleValueChanged is used instead of TryParseValueFromString
		// When TryParseValueFromString is used (pre net8), invalid input is replaced by previous value.		
		bool parsingFailed;
		_validationMessageStore.Clear(FieldIdentifier);

		if (HxInputDate<DateTime>.TryParseDateTimeOffsetFromString(newInputValue, null, out var date))
		{
			parsingFailed = false;
			CurrentValue = GetValueFromDateTimeOffset(date);
		}
		else
		{
			parsingFailed = true;
			_validationMessageStore.Add(FieldIdentifier, ParsingErrorMessageEffective);
		}

		// We can skip the validation notification if we were previously valid and still are
		if (parsingFailed || _previousParsingAttemptFailed)
		{
			EditContext.NotifyValidationStateChanged();
			_previousParsingAttemptFailed = parsingFailed;
		}
#endif
	}

Why are the so different NET8 vs pre-NET8?

[hakenr]

@jirikanda Before .NET 8, the SetUpdatesAttributeName() method was missing, and some of our components, such as HxInputDate, compensated it by using our own logic. In .NET 8, the new InputBase implementation incorporates SetUpdatesAttributeName() along with _incomingValueBeforeParsing and other stuff from my pull request, making our custom logic obsolete. Now, the InputBase already addresses the issue we were compensating for, simplifying the process to just CurrentValueAsString = newInputValue;.

dotnet/aspnetcore#46434

[hakenr]

We should be able to drop all these pre-net8 "branches" in November 2024:
https://dotnet.microsoft.com/en-us/platform/support/policy/dotnet-core