OneWay/Onetime binder with more options

[Trigve]

Hi,
I'm using Aspid.MVVM in my project (https://github.com/Trigve/Ja2xUnity) and I've came across the situation, when I have a value binder (OneTime or OneWay which is used for initial value initialization or value reset without "callbacks" back to the VM). Now, in some situation I need to set the value on the target but WITHOUT notification. For instance, uGUI Slider does have SetValueWithoutNotify() which could be used, but binder are always setting the value directly using property (which will emit the event). So the solutions now are hacky (inheriting control, various additional components, ...).

The one option I see is to add additional attribute parameter to the binder, like for instance OneTimeBind(Notify = false)]. Or is there any other clean solution?

[Joaquincuevas]

Good news first: the built-in slider binder already doesn’t notify the ViewModel when it sets the value. In SliderValueMonoBinder.SetValue the write is wrapped in an _isNotifyValueChanged = false guard, and in OneWay/OneTime mode the binder never even subscribes to onValueChanged. So nothing echoes back to the VM.

What does happen is that slider.value = … raises Slider.onValueChanged for other listeners (your own scripts, UnityEvents in the inspector). That’s documented in the binder’s remarks. If those are what you want to keep quiet, you don’t need to subclass the control: a small custom binder using SetValueWithoutNotify is enough.

csharp
using UnityEngine;
using UnityEngine.UI;
using Aspid.MVVM;
using Aspid.MVVM.StarterKit;

[BindModeOverride(IsOne = true)] // OneWay / OneTime only
[AddComponentMenu("Aspid/MVVM/Binders/UI/Slider/Slider Binder – Value (Silent)")]
public partial class SliderSilentValueMonoBinder : ComponentMonoBinder, IFloatBinder
{
[SerializeReference] private IConverter<float, float> _converter;

public void SetValue(float value)
{
    var slider = CachedComponent;
    var converted = _converter?.Convert(value) ?? value;
    slider.SetValueWithoutNotify(Mathf.Clamp(converted, slider.minValue, slider.maxValue));
}

}
Since it implements IFloatBinder, int/double/etc. properties bind to it too, like the stock binder.
Keep it partial: the package’s source generators expect that on MonoBinders.
The same pattern works for other controls with a …WithoutNotify method (Toggle.SetIsOnWithoutNotify, InputField.SetTextWithoutNotify, Dropdown.SetValueWithoutNotify, Scrollbar.SetValueWithoutNotify).

A Notify = false option on the stock binders would be a nice built-in. If you want it upstream, it’s worth opening as a feature request.

If this helps, please mark it as the answer.

[Trigve]

Thanks for the quick reply.
Yes, I mostly interested in suppressing the Slider.onValueChanged for other listeners. Using the custom binder is an option, but I don't think creating new binder class just for this is optimal/clean solution (when the infrastructure is already there). In my current use-case, I have already inherited Toggle so doing it there was of less hassle then creating new binder.

Just for information what concrete problem I'm trying to solve: I have a VirtualList, where item prefab is a GO with Toggle. When user clicks the toggle, the sound is being played (and it should be played only on "external" clicks). The problem is, that because VirtualList is pooling the item GOs already instantiated, every time the item GO gets reactivated, the sound is played (the same could happen during initialization of the VirtualList).

I'll open the feature request then.

[VPDPersonal]

Thanks to Joaquincuevas for the workaround. Tracked in #276, where I've proposed a Notify Mode setting on the value binders (Always, ExceptOnBind, Never) to write ViewModel values without raising onValueChanged.

[Trigve]

@VPDPersonal After the several re-read of Joaquincuevas answer I have the impression, that answer was AI generated as the original poster doesn't have any repos with C# or Unity (but it could have those, just private) and his discussion history never mentioned anything about C# or Unity or MVVM :)

[VPDPersonal]

Possibly :)