The correct way to raise propertychanged in ReactiveUI

Question

Sometimes I need to raise propertychanged for a related property, like this:

public bool IsValid
    {
        get { return _isValid; }
        set
        {
            if (value.Equals(_isValid)) return;
            _isValid = value;
            OnPropertyChanged("IsValid");
            OnPropertyChanged("IsSavable");
        }
    }

I could write it like this:

public bool IsValid
    {
        get { return _isValid; }
        set
        {
            if (value.Equals(_isValid)) return;
            _isValid = value;
            this.RaisePropertyChanged("IsValid");
            this.RaisePropertyChanged("IsSavable");
        }
    }

Code based on Paul's answer:

    public ViewModelBase()
    {
        Validator = new AlwaysTrueValidValidator<ViewModelBase>();
        // logic for IsSavable
        this.WhenAny(x => x.IsValid, x => x.IsDirty, x => x.IsBusy, (valid, dirty, busy) => valid.Value && dirty.Value && busy.Value == false)
            .ToProperty(this, x => x.IsSavable, out _isSavable);
    }

    readonly ObservableAsPropertyHelper<bool> _isSavable;
    public bool IsSavable
    {
        get { return _isSavable.Value; }
    }

    [UsedImplicitly]
    public bool IsValid
    {
        get { return _isValid; }
        set { this.RaiseAndSetIfChanged(ref _isValid, value); }
    }

    public void OnPropertyChanged(string property)
    {
        // ReSharper disable once ExplicitCallerInfoArgument
        this.RaisePropertyChanged(property);
    }

As you can see the code is a lot cleaner it's all get/set and the logic is in one place.

Is there a smarter way to do it? Yes

score 5 · Accepted Answer · answered Dec 21 '14 at 09:55

5

In ReactiveUI, the desire to do this means that you are Doing It Wrong (or at least, not the RxUI way). IsSaveable is related to IsValid, you should describe that using WhenAny and ToProperty. Maybe you could write that as:

this.WhenAny(x => x.IsValid, x => x.IsChanged, (valid, changed) => valid.Value && changed.Value)
    .ToProperty(this, x => x.IsSavable, out isSavable);

answered Dec 21 '14 at 09:55

Ana Betts

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So the properties should all be dumb get/setters and the interaction logic for the properties should be set up in the constructor? – Martin Andersen Dec 21 '14 at 11:09
Yeah, they should use RaiseAndSetIfChanged, and the interaction is set up in the constructor – Ana Betts Dec 21 '14 at 13:19
From the ReactiveUI docs...Property vs ObservableAsPropertyHelper You should use a property and RaiseAndSetIfChanged if you are intending to mutate the value – ShhTot Sep 29 '20 at 15:59
1

How to notify several properties upon a single property? – Shimmy Weitzhandler Dec 05 '21 at 03:42

The correct way to raise propertychanged in ReactiveUI

1 Answers1